Name: preparation of mica supported lipid bilayers for high resolution optical microscopy imaging
Uploaded: 2014-06-07T15:00:00.000+00:00
Duration: 7 min 48 s
Description: Watch this Scientific Journal Video about Preparation of Mica Supported Lipid Bilayers for High Resolution Optical Microscopy Imaging at JoVE.com

The authors have no acknowledgements.

1. Mica and&#160;Slides&#160;Preparation
<ol>
	<li>Place No. 1&#189; (0.17 mm) coverslips into staining rack.</li>
	<li>Sonicate for 30 min in 2% detergent at 60 &#176;C.</li>
	<li>Wash 20 times with deionized water.</li>
	<li>Remove slides using forceps and blow dry using compressed air or nitrogen.</li>
	<li>Cut mica sheet into 10 x 10 mm square pieces using scissors or razor blade.</li>
	<li>Cut each mica piece into 2-3 thinner leaflets using razor blade. 
	NOTE: This step requires use of sharp blade.</li>
</ol>
2. Mica Assembly and Chamber Mounting
<ol>
	<li>Clean microscopic glass slide with ethanol.</li>
	<li>Glue leaflet of mica cut in step 1.6 to glass slide using optical adhesive. Low viscosity adhesive is advised to better spread the drop and glue the mica.</li>
	<li>Cure under UV lamp, 10 min. 
	NOTE: Adhesive is cured by UV light with maximum absorption in the range of 350 to 380nm and the recommended energy required for full cure is 4.5 J/cm2. However, different light sources can be used for this step (see materials provided by adhesive supplier).</li>
	<li>Expose a clean mica surface by removing the first few layers with Scotch tape.</li>
	<li>Place small drop (~20 &#956;m) of optical adhesive onto the mica surface. 
	NOTE: At this step, high viscosity adhesive with low autofluorescence level is advised. Our experience showed that using combination of low (step 2.2) and high viscosity adhesives increases significantly effectiveness of mica splitting (step 2.7).</li>
	<li>Gently place freshly cleaned coverslip onto the drop of adhesive, avoiding air bubbles, let settle for 1 min.</li>
	<li>Cure under UV lamp, 10 min. 
	NOTE: after this step, the sandwich of glass slide, mica and coverslip can be stored for a relatively long period of time (up to few weeks). Proceed to the next step just before the actual SLB preparation, to make sure the mica surface is fresh. 
	NOTE: Adhesive is cured by UV light with maximum absorption in the range of 350 to 380nm and the recommended energy required for full cure is 4.5J/cm2. However, different light sources can be used for this step (see materials provided by adhesive supplier).</li>
	<li>Using an exacto knife, gently dismount the coverslip from side glass slide as shown in the video. In most cases, a thin and flat layer of mica will remain attached to the coverslip. Mica attached to glass slide can be reused (repeat from step 2.4).</li>
	<li>Check the surface quality by naked eye or under a dissecting microscope, to make sure that mica layer is still glued to the coverslip and was not removed completely during splitting in step 2.8. Making a small scratch with a forceps or dissecting needle will help to distinguish between the adhesive which has a detectably different consistency from mica.</li>
	<li>Remove rubber seal from a 1.5 ml vial cap and glue the cap upside down to the surface using optical adhesive or nail polish, and cure with UV lamp, or let air dry 10 min, respectively. 
	NOTE: If the sample is prepared for simultaneous optical (TIRFM or confocal) with AFM imaging, a 1.5 ml vial cap might be too small to mount the AFM head on the microscope stage. In that case, the cap might be substituted by any plastic O-ring with a bigger diameter, suitable for AFM head mounting. In case when the experiment requires removing the cap without damaging the mica surface, silicone grease can be used instead of glue or nail polish.</li>
</ol>
3. Supported Lipid Bilayer (SLB) Formation
<ol>
	<li>Place freshly prepared liposome solution into chamber with surface. The minimum volume required for SLB formation is ~30 &#956;l. 
	NOTE: For more details on the liposome and SLB formation, refer to published protocols, such as such as Bag et&#160;al., 201415.</li>
	<li>Proceed with SLB formation using desired protocol. During incubation and imaging, the chamber can be placed in a heat-block or heated microscope stage to maintain temperature required to keep the lipids being used above their melting temperature.</li>
</ol>

<ol>
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F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanoscale+analysis+of+supported+lipid+bilayers+using+atomic+force+microscopy.">Nanoscale analysis of supported lipid bilayers using atomic force microscopy.</a> Biochimica et Biophysica Acta (BBA) - Biomembranes. 1798, 750-765 (2010).</li><li>Szmodis, A. W., Blanchette, C. D., Longo, M. L., Orme, C. A., Parikh, A. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Thermally+induced+phase+separation+in+supported+bilayers+of+glycosphingolipid+and+phospholipid+mixtures.">Thermally induced phase separation in supported bilayers of glycosphingolipid and phospholipid mixtures.</a> Biointerphases. 5, 120-130 (2010).</li><li>Strulson, M. K., Maurer, J. 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M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Combined+scanning+probe+and+total+internal+reflection+fluorescence+microscopy.">Combined scanning probe and total internal reflection fluorescence microscopy.</a> Methods. 46, 2-10 (2008).</li><li>Shaw, J. E., Slade, A., Yip, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+in+situ+total+internal+reflectance+fluorescence/atomic+force+microscopy+studies+of+DPPC/dPOPC+microdomains+in+supported+planar+lipid+bilayers.">Simultaneous in situ total internal reflectance fluorescence/atomic force microscopy studies of DPPC/dPOPC microdomains in supported planar lipid bilayers.</a> J Am Chem Soc. 125, 11838-11839 (2003).</li><li>Skaug, M. J., Faller, R., Longo, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correlating+anomalous+diffusion+with+lipid+bilayer+membrane+structure+using+single+molecule+tracking+and+atomic+force+microscopy.">Correlating anomalous diffusion with lipid bilayer membrane structure using single molecule tracking and atomic force microscopy.</a> J Chem Phys. 134, (2011).</li><li>Bag, N., Yap, D. H., Wohland, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temperature+dependence+of+diffusion+in+model+and+live+cell+membranes+characterized+by+imaging+fluorescence+correlation+spectroscopy.">Temperature dependence of diffusion in model and live cell membranes characterized by imaging fluorescence correlation spectroscopy.</a> Biochimica et Biophysica Acta. , (2013).</li><li>Sbalzarini, I. F., Koumoutsakos, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Feature+point+tracking+and+trajectory+analysis+for+video+imaging+in+cell+biology.">Feature point tracking and trajectory analysis for video imaging in cell biology.</a> J Struct Biol. 151, 182-195 (2005).</li><li>Linkert, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metadata+matters:+access+to+image+data+in+the+real+world.">Metadata matters: access to image data in the real world.</a> J Cell Biol. 189, 777-782 (2010).</li><li>Schutz, G. J., Schindler, H., Schmidt, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Single-molecule+microscopy+on+model+membranes+reveals+anomalous+diffusion.">Single-molecule microscopy on model membranes reveals anomalous diffusion.</a> Biophys J. 73, 1073-1080 (1997).</li><li>Matysik, A., Kraut, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=TrackArt:+the+user+friendly+interface+for+single+molecule+tracking+data+analysis+and+simulation+applied+to+complex+diffusion+in+mica+supported+lipid+bilayers.">TrackArt: the user friendly interface for single molecule tracking data analysis and simulation applied to complex diffusion in mica supported lipid bilayers.</a> BMC Research Notes. 7, (2014).</li></ol>

The authors have nothing to disclose.

This protocol describes a method for preparing smooth and thin mica surfaces for lipid bilayer deposition and high resolution imaging. The technique requires minimal manual skills, limited mostly to the careful disassembly of the glass-mica-glass sandwich (step 2.8), which is critical for obtaining a high quality mica surface. Inspection of the freshly cleaved mica is always required at this point, since it is possible for the mica to detach from the optical adhesive without cleaving, leaving exposed areas of optical adhesive. That might result in unwanted deposition of the bilayer on adhesive instead of on the mica. The mica surface prepared using the method described is with few exceptions parallel to the coverslip surface, judging by the uniformly high optical imaging quality we obtained; we therefore did not see a need for additional verification.
The final step in mounting the chamber can be customized. The Video tutorial shows a 1.5 ml glass vial plastic cap being used as a chamber, however this can be substituted with any object of similar shape and desired dimensions, e.g. for simultaneous AFM-TIRFM/confocal imaging, where the sample with its holder has to fit into the AFM head. Mounting of a custom chamber can be skipped, if imaging is to be performed using a standard, 35 mm metal cell chamber. In this case however, a 25 mm round cover glass has to be used, and a much bigger volume of liposome solution would be required for SLB formation.
The results presented here show that single molecule imaging and tracking can be easily done on extremely flat mica surfaces thin enough to be amenable to TIRFM imaging, according to the protocol for surface preparation described. The same preparation can be applied to other techniques, including high resolution optical microscopy, such as total internal reflection fluorescence correlation spectroscopy (TIR-FCS). Importantly, SLBs prepared in the same way (or even the exact same samples) can be used in both experimental setups, an essential criterion for direct comparison of results obtained using different methods, e.g. AFM, SMT, FCS, and FRAP.

The overall goal of the present protocol is to show a method for preparing mica surfaces for high resolution imaging of mica supported lipid bilayers (SLBs) using optical total internal reflection fluorescence microscopy (TIRFM) or confocal microscopy, which could also be combined with atomic force microscopy (AFM).
SLBs are a widely used model for numerous studies of lipid clustering, phase separation, dynamics of bilayer components or their interactions with peptides, proteins or other compounds1-5. Different substrates might be used for SLB formation (i.e. glass, mica, silicon dioxide, polymers) depending on the nature of the study4,6-8. Typical membrane studies rely on microscopy-based imaging techniques, such as TIRFM and AFM. Thus, for TIRFM imaging, a glass surface is a typical choice because glass is transparent. Preparation of glass is relatively easy, and the quality of the results is primarily determined by thorough surface cleaning prior to deposition of lipid vesicles. AFM due to its high axial resolution requires mica surfaces. Mica is a silicate mineral, with close to perfect basal cleavage. Thus, the freshly cleaved mica is atomically flat, allowing observation of membrane height differences even at the sub-nanometer scale9.
Diffusion studies using methods such as fluorescence correlation spectroscopy (FCS), single molecule tracking (SMT), and fluorescence recovery after photobleaching (FRAP) showed however, that lipid membrane dynamics depend heavily on the type of surface onto which they are deposited, whereby glass and mica can give widely varying results10,11. These differences include not only the diffusion coefficients of the membrane probes, but also the detection of separate populations of particles diffusing with different rates, and possibly switching between different states.
Thus, the direct comparison of results obtained using TIRFM and AFM techniques is often problematic, unless the same surface (in this case mica) is used. Although there are some studies where TIRFM and AFM bilayer imaging was conducted on the same mica surface12,13, mica is rarely used for optical microscopy, mostly because of handling problems. Mica preparation requires cutting by hand into thin leaflets, which are then glued to the coverslip using optical adhesive12. This method however requires some practice to achieve satisfactory results. Moreover, the surfaces obtained are often wavy and thick, making them difficult to use with low working distance, high numerical aperture lenses.
Mica surfaces prepared as described in this protocol are very thin (~220 &#956;m, including the coverslip thickness of 170 &#956;m) and extremely flat, avoiding &#8220;waviness&#8221;, which is critical for successful high resolution imaging. They can be used for TIRFM or confocal setups. Moreover, the same samples can be transferred to AFM, and even imaged simultaneously with TIRFM/confocal and AFM. Combining these two techniques allows direct correlation of diffusion behavior with bilayer membrane structure14. Because mica surfaces are freshly cleaved, they are clean and do not require time consuming, poorly reproducible, and potentially dangerous cleaning procedures (glass cleaning protocols usually include chemicals such as Piranha solution, sulfuric acid, sodium/potassium hydroxide). Mounting of a small chamber, also described in the protocol, reduces the volume of vesicles required for effective bilayer formation to less than 50 &#956;l. Finally, the whole process of surface assembly is not time consuming (preparation takes less than 30 min), and does not require a high degree of manual skill, as does conventional mica cleavage and gluing.

<table><tbody><tr><td>Bath Sonicator</td><td>Fisher Scientific</td><td>FB15051</td><td></td></tr><tr><td>Coverslips 24 x 50 mm - No H1.5</td><td>Marienfeld</td><td>102222</td><td></td></tr><tr><td>DOPC</td><td>Avanti Polar Lipids</td><td>850357</td><td></td></tr><tr><td>Hellmanex III (detergent)</td><td>Hellma Analytics</td><td>320.003</td><td></td></tr><tr><td>Mica V-1 Grade</td><td>SPI Suppliers</td><td>1872-CA</td><td></td></tr><tr><td>Optical Adhesive (high viscosity)</td><td>Norland Products</td><td>NOA63</td><td></td></tr><tr><td>Optical Adhesive (low viscosity)</td><td>Norland Products</td><td>NOA60</td><td></td></tr><tr><td>Sphingomyelin-ATTO647N</td><td>AttoTec</td><td>AD 647N-171</td><td></td></tr><tr><td>UV lamp</td><td>Synoptics Ltd.</td><td>GelVue GVM20</td><td>The lamp was set to 100% power</td></tr></tbody></table>

preparation of mica supported lipid bilayers for high resolution optical microscopy imaging

Supported lipid bilayers (SLBs) are widely used as a model for studying membrane properties (phase separation, clustering, dynamics) and its interaction with other compounds, such as drugs or peptides. However SLB characteristics differ depending on the support used. 
Commonly used techniques for SLB imaging and measurements are single molecule fluorescence microscopy, FCS and atomic force microscopy (AFM). Because most optical imaging studies are carried out on a glass support, while AFM requires an extremely flat surface (generally mica), results from these techniques cannot be compared directly, since the charge and smoothness properties of these materials strongly influence diffusion. Unfortunately, the high level of manual dexterity required for the cutting and gluing thin slices of mica to the glass slide presents a hurdle to routine use of mica for SLB preparation. Although this would be the method of choice, such prepared mica surfaces often end up being uneven (wavy) and difficult to image, especially with small working distance, high numerical aperture lenses. Here we present a simple and reproducible method for preparing thin, flat mica surfaces for lipid vesicle deposition and SLB preparation. Additionally, our custom made chamber requires only very small volumes of vesicles for SLB formation. The overall procedure results in the efficient, simple and inexpensive production of high quality lipid bilayer surfaces that are directly comparable to those used in AFM studies.

The diffusion behavior of fluorescent lipid probes in SLBs is different depending on the substrate. TIRFM combined with the SMT technique is a valuable method for visualizing particle movements and extracting their diffusion coefficients. Single molecule signals of a Sphingomyelin-ATTO647N probe diffusing in a DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) bilayer supported on glass and mica are shown on the attached animated figure. The mica surface was prepared according to the protocol presented here. To estimate optical aberrations, full width at half maximum (FWHM) was measured and averaged over the 20 point spread function (PSF) using Mosaic 2D PSF Size ImageJ plugin16,17. The measured FWHM for glass and mica were 441nm and 464nm respectively (Figure 1). The 22nm difference in resolution between imaging on glass and mica is not significant. In both cases, the PSF centroid of each single fluorescent molecule can be localized in successive frames, and linked into particle trajectories over time with Mosaic Particle Tracker ImageJ plugin16,17. Figure 2 shows sample trajectories of particles diffusing across the bilayer supported on both surfaces. The mean square displacements (MSDs) of the fluorescent probe diffusing in DOPC membrane supported on glass and mica was plotted on the Figure 3. Due to coexistence of multiple populations two population model was used to extract fast and slow diffusion coefficients, according to method described by Schutz (Figure 4, Figure 5)18. The diffusion coefficients and their fractions were extracted using TrackArt software19 and are summarized in Table 1.
The results from this example prove the existence of two separate states of the diffusing probe: fast and slow. The diffusion coefficient of the fast population is roughly 1.5 times higher on mica than on glass. The slow component however, is almost immobile on glass (&#60;0.01 &#956;m2/sec), compared to a D of only ~1/10 the fast population on mica.
<img alt="Figure 1" fo:content-width="5in" src="/files/ftp_upload/52054/52054fig1highres.jpg" width="500" /> 
Figure 1.&#160;Average PSF size. Average PSF intensity profile for 20 spots measured on glass (black solid line) and mica (red dashed line). The full width at half maximum (FWHM) of the normalized intensity for glass and mica was estimated to be 441 nm and 464 nm, respectively. The 22nm difference indicates that there is no significant drop in imaging resolution between these two surfaces. PSF intensity profile was measured using Mosaic PSF 2D Tool ImageJ plugin16,17. <a href="https://www.jove.com/files/ftp_upload/52054/52054fig1highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" fo:content-width="5in" src="/files/ftp_upload/52054/52054fig2highres.jpg" width="500" /> 
Figure 2.&#160;Sample trajectories. Sample trajectories of SM-ATTO647N diffusing in a DOPC lipid bilayer supported on glass (A) and mica (B). On the glass supported bilayer, the probe is often immobilized on the surface, occasionally switching to the fast diffusing state. Probes diffusing on the mica supported bilayer, in contrast, are rarely immobilized on the surface. Instead, they tend to switch between fast and slow diffusing state. <a href="https://www.jove.com/files/ftp_upload/52054/52054fig2highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" fo:content-width="5in" src="/files/ftp_upload/52054/52054fig3highres.jpg" width="500" /> 
Figure 3.&#160;Mean square displacements. Mean square displacements of SM-ATTO647N particles diffusing on a glass- (&#9632;) and mica- (&#9679;) supported DOPC bilayer. <a href="https://www.jove.com/files/ftp_upload/52054/52054fig3highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" fo:content-width="5in" src="/files/ftp_upload/52054/52054fig4highres.jpg" width="500" /> 
Figure 4.&#160;Cumulative probability distribution fits. Cumulative probability distribution (CPD) of square displacements and fits for the bi-exponential (two-population) diffusion model of SM-ATTO647N particles diffusing on glass- (A) and mica- (B) supported DOPC bilayers. Distributions and fits are presented only for the fifthtime-lag (&#916;t&#160;= 50 msec). Calculations and plots are obtained using TrackArt19 software. <a href="https://www.jove.com/files/ftp_upload/52054/52054fig4highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" fo:content-width="5in" src="/files/ftp_upload/52054/52054fig5highres.jpg" width="500" /> 
Figure 5.&#160;MSD and fraction plots. MSD plots for the fast (r12) and slow (r22) diffusing population and fraction of the fast population (F1) calculated from the CPD fits. Results are presented separately for SM-ATTO647N particles diffusing on glass- (A) and mica- (B) supported DOPC bilayers. Calculations and plots were obtained using TrackArt19 software. <a href="https://www.jove.com/files/ftp_upload/52054/52054fig5highres.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<table border="0" cellpadding="0" cellspacing="0" width="672">
	<tbody>
		<tr height="46">
			<td height="46" style="height:46px;width:72px;"></td>
			<td colspan="4" style="width:301px;">Population 1 (fast)</td>
			<td colspan="4" style="width:301px;">Population 2 (slow)</td>
		</tr>
		<tr height="67">
			<td height="67" style="height:67px;width:72px;"></td>
			<td colspan="2" style="width:136px;">D1 (&#956;m2/sec)</td>
			<td colspan="2" style="width:165px;">Fraction (%)</td>
			<td colspan="2" style="width:136px;">D2 (&#956;m2/sec)</td>
			<td colspan="2" style="width:165px;">Fraction (%)</td>
		</tr>
		<tr height="51">
			<td height="51" style="height:51px;width:72px;">Glass</td>
			<td colspan="2" style="width:136px;">1.840 &#177; 0.031</td>
			<td colspan="2" style="width:165px;">65.19 &#177; 0.56</td>
			<td colspan="2" style="width:136px;">0.006 &#177; 0.001</td>
			<td colspan="2" style="width:165px;">34.81 &#177; 0.56</td>
		</tr>
		<tr height="52">
			<td height="52" style="height:52px;">Mica</td>
			<td colspan="2">2.440 &#177; 0.023</td>
			<td colspan="2">53.88 &#177; 0.26</td>
			<td colspan="2">0.176 &#177; 0.002</td>
			<td colspan="2" style="width:165px;">46.12 &#177; 0.26</td>
		</tr>
	</tbody>
</table>
Table 1.&#160;Diffusion coefficients. Summary of diffusion statistics. Diffusion coefficients for slow and fast populations and their fractions. Calculations were performed in TrackArt software using a two population model. Trajectories were recognized and linked using Mosaic Particle Tracker ImageJ plugin.
<a href="https://www.jove.com/files/ftp_upload/52054/1.mp4" target="_blank">Animated Figure</a>: Single molecules diffusion. Timelapse TIRFM movie of Sphingomyelin-ATTO647N diffusing in a DOPC bilayer supported on glass (left) and mica (right). Scale bar is 5 &#956;m.

Watch this Scientific Journal Video about Preparation of Mica Supported Lipid Bilayers for High Resolution Optical Microscopy Imaging at JoVE.com

Preparation of Mica Supported Lipid Bilayers for High Resolution Optical Microscopy Imaging

We present a method of preparing mica supported lipid bilayers for high resolution microscopy. Mica is transparent and flat on an atomic scale, but rarely used in imaging because of handling difficulties; our preparation results in even deposition of the mica sheet, and reduces the material used in bilayer preparation.

Supported lipid bilayers (SLBs) are widely used as a model for studying membrane properties (phase separation, clustering, dynamics) and its interaction ...

preparation-mica-supported-lipid-bilayers-for-high-resolution-optical

Nanyang Technological University

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Bioengineering

13.3K Views.  Nanyang Technological University. We present a method of preparing mica supported lipid bilayers for high resolution microscopy. Mica is transparent and flat on an atomic scale, but rarely used in imaging because of handling difficulties; our preparation results in even deposition of the mica sheet, and reduces the material used in bilayer preparation.

Video: Preparation of Mica Supported Lipid Bilayers for High Resolution Optical Microscopy Imaging

Supported Planar Bilayers for the Formation of Study of Immunological Synapses and Kinapse

Supported planar bilayers are powerful tools that can be used to model the molecular interactions in an immunological synapse.   To mimic the interactions between lymphocytes and antigen presenting cells, we use Ni2+-chelating lipids to anchor recombinant cell adhesion and MHC proteins to the upper leaflet of a bilayer with poly-histidine tags. Planar bilayers are generated by preparing lipid, treating the glass surfaces where the bilayer will form, and then forming the bilayer in a specialized chamber containing a flow-cell where the lymphocytes will be added.  Then, bilayers are charged with Ni and his-tagged recombinant proteins are added.  Finally,  lymphocytes are injected into the flow cell and TIRF microscopy can be used to image synapse formation and the mechanisms that control T cell locomotion, sites of receptor sorting,  and sites of receptor degradation.

Supported planar bilayers are powerful tools that can be used to model the molecular interactions in an immunological synapse. Here, we show methods for anchoring cell adhesion proteins known to modulate synapse formation to the upper leaflet of the lipid bilyer and visualize synapse formation using TIRF microscopy.

Supported planar bilayers are powerful tools that can be used to model the molecular interactions in an immunological synapse.   To mimic the interactions ...

Biology

Formation of Biomembrane Microarrays with a Squeegee-based Assembly Method

Lipid bilayer membranes form the plasma membranes of cells and define the boundaries of subcellular organelles. In nature, these membranes are heterogeneous mixtures of many types of lipids, contain membrane-bound proteins and are decorated with carbohydrates. In some experiments, it is desirable to decouple the biophysical or biochemical properties of the lipid bilayer from those of the natural membrane. Such cases call for the use of model systems such as giant vesicles, liposomes or supported lipid bilayers (SLBs). Arrays of SLBs are particularly attractive for sensing applications and mimicking cell-cell interactions. Here we describe a new method for forming SLB arrays. Submicron-diameter SiO2 beads are first coated with lipid bilayers to form spherical SLBs (SSLBs). The beads are then deposited into an array of micro-fabricated submicron-diameter microwells. The preparation technique uses a "squeegee" to clean the substrate surface, while leaving behind SSLBs that have settled into microwells. This method requires no chemical modification of the microwell substrate, nor any particular targeting ligands on the SSLB. Microwells are occupied by single beads because the well diameter is tuned to be just larger than the bead diameter. Typically, more 75% of the wells are occupied, while the rest remain empty. In buffer SSLB arrays display long-term stability of greater than one week. Multiple types of SSLBs can be placed in a single array by serial deposition, and the arrays can be used for sensing, which we demonstrate by characterizing the interaction of cholera toxin with ganglioside GM1. We also show that phospholipid vesicles without the bead supports and biomembranes from cellular sources can be arrayed with the same method and cell-specific membrane lipids can be identified.

Supported lipid bilayers and natural membrane particles are convenient systems that can approximate the properties of cell membranes and be incorporated in a variety of analytical strategies. Here we demonstrate a method for preparing microarrays composed of supported lipid bilayer-coated SiO2 beads, phospholipid vesicles or natural membrane particles.

Lipid bilayer membranes form the plasma membranes of cells and define the boundaries of subcellular organelles. In nature, these membranes are ...

Atomic Force Microscopy Imaging and Force Spectroscopy of Supported Lipid Bilayers

Atomic force microscopy (AFM) is a versatile, high-resolution imaging technique that allows visualization of biological membranes. It has sufficient magnification to examine membrane substructures and even individual molecules. AFM can act as a force probe to measure interactions and mechanical properties of membranes. Supported lipid bilayers are conventionally used as membrane models in AFM studies. In this protocol, we demonstrate how to prepare supported bilayers and characterize their structure and mechanical properties using AFM. These include bilayer thickness and breakthrough force. 
The information provided by AFM imaging and force spectroscopy help define mechanical and chemical properties of membranes. These properties play an important role in cellular processes such as maintaining cell hemostasis from environmental stress, bringing membrane proteins together, and stabilizing protein complexes.

We describe a protocol for preparation of supported lipid bilayers and its characterization using atomic force microscopy and force spectroscopy.

Atomic force microscopy (AFM) is a versatile, high-resolution imaging technique that allows visualization of biological membranes. It has sufficient ...

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer (SALB) Method

In order to mimic cell membranes, the supported lipid bilayer (SLB) is an attractive platform which enables in vitro investigation of membrane-related processes while conferring biocompatibility and biofunctionality to solid substrates. The spontaneous adsorption and rupture of phospholipid vesicles is the most commonly used method to form SLBs. However, under physiological conditions, vesicle fusion (VF) is limited to only a subset of lipid compositions and solid supports. Here, we describe a one-step general procedure called the solvent-assisted lipid bilayer (SALB) formation method in order to form SLBs which does not require vesicles. The SALB method involves the deposition of lipid molecules onto a solid surface in the presence of water-miscible organic solvents (e.g., isopropanol) and subsequent solvent-exchange with aqueous buffer solution in order to trigger SLB formation. The continuous solvent exchange step enables application of the method in a flow-through configuration suitable for monitoring bilayer formation and subsequent alterations using a wide range of surface-sensitive biosensors. The SALB method can be used to fabricate SLBs on a wide range of hydrophilic solid surfaces, including those which are intractable to vesicle fusion. In addition, it enables fabrication of SLBs composed of lipid compositions which cannot be prepared using the vesicle fusion method. Herein, we compare results obtained with the SALB and conventional vesicle fusion methods on two illustrative hydrophilic surfaces, silicon dioxide and gold. To optimize the experimental conditions for preparation of high quality bilayers prepared via the SALB method, the effect of various parameters, including the type of organic solvent in the deposition step, the rate of solvent exchange, and the lipid concentration is discussed along with troubleshooting tips. Formation of supported membranes containing high fractions of cholesterol is also demonstrated with the SALB method, highlighting the technical capabilities of the SALB technique for a wide range of membrane configurations.

Biomembrane Fabrication by the Solvent-assisted Lipid Bilayer SALB Method

We present an experimental protocol to form a supported lipid bilayer on solid substrates without using lipid vesicles. We demonstrate a one-step method to form a lipid bilayer on silicon dioxide and gold as well as supported membranes with cholesterol-enriched domain for various biological applications.

In order to mimic cell membranes, the supported lipid bilayer (SLB) is an attractive platform which enables in vitro investigation of membrane-related ...

Single Molecule Fluorescence Microscopy on Planar Supported Bilayers

In the course of a single decade single molecule microscopy has changed from being a secluded domain shared merely by physicists with a strong background in optics and laser physics to a discipline that is now enjoying vivid attention by life-scientists of all venues 1. This is because single molecule imaging has the unique potential to reveal protein behavior in situ in living cells and uncover cellular organization with unprecedented resolution below the diffraction limit of visible light 2. Glass-supported planar lipid bilayers (SLBs) are a powerful tool to bring cells otherwise growing in suspension in close enough proximity to the glass slide so that they can be readily imaged in noise-reduced Total Internal Reflection illumination mode 3,4. They are very useful to study the protein dynamics in plasma membrane-associated events as diverse as cell-cell contact formation, endocytosis, exocytosis and immune recognition. Simple procedures are presented how to generate highly mobile protein-functionalized SLBs in a reproducible manner, how to determine protein mobility within and how to measure protein densities with the use of single molecule detection. It is shown how to construct a cost-efficient single molecule microscopy system with TIRF illumination capabilities and how to operate it in the experiment.

Preparation of protein-functionalized planar glass-supported lipid bilayers, determination of protein mobility within and measurement of protein densities is shown here. A roadmap to building a noise-reduced Total Internal Reflection microscope is outlined, which allows visualizing single bilayer-resident fluorochromes with high spatiotemporal resolution.

In the course of a single decade single molecule microscopy has changed from being a secluded domain shared merely by physicists with a strong background ...

Sample Preparation using a Lipid Monolayer Method for Electron Crystallographic Studies

Electron crystallography is a powerful tool for high-resolution structure determination. Macromolecules such as soluble or membrane proteins can be grown into highly ordered two-dimensional (2D) crystals under favorable conditions. The quality of the grown 2D crystals is crucial to the resolution of the final reconstruction via 2D image processing. Over the years, lipid monolayers have been used as a supporting layer to foster the 2D crystallization of peripheral membrane proteins as well as soluble proteins. This method can also be applied to 2D crystallization of integral membrane proteins but requires more extensive empirical investigation to determine detergent and dialysis conditions to promote partitioning to the monolayer. A lipid monolayer forms at the air-water interface such that the polar lipid head groups remain hydrated in the aqueous phase and the non-polar, acyl chains, tails partition into the air, breaking the surface tension and flattening the water surface. The charged nature or distinctive chemical moieties of the head groups provide affinity for proteins in solution, promoting binding for 2D array formation. A newly formed monolayer with the 2D array can be readily transfer into an electron microscope (EM) on a carbon-coated copper grid used to lift and support the crystalline array. In this work, we describe a lipid monolayer methodology for cryogenic electron microscopic (cryo-EM) imaging.

Lipid monolayers have been used as a foundation for forming two-dimensional (2D) protein crystals for structural studies for decades. They are stable at the air-water interface and can serve as a thin supporting material for electron imaging. Here we present the proven steps on preparing lipid monolayers for biological studies.

Electron crystallography is a powerful tool for high-resolution structure determination. Macromolecules such as soluble or membrane proteins can be grown ...

Biochemistry

Single-Molecule Diffusion and Assembly on Polymer-Crowded Lipid Membranes

Cellular membranes are highly crowded environments for biomolecular reactions and signaling. Yet, most in vitro experiments probing protein interaction with lipids employ naked bilayer membranes. Such systems lack the complexities of crowding by membrane-embedded proteins and glycans and exclude the associated volume effects encountered on cellular membrane surfaces. Also, the negatively charged glass surface onto which the lipid bilayers are formed prevents the free diffusion of transmembrane biomolecules. Here, we present a well-characterized polymer-lipid membrane as a mimic for crowded lipid membranes. This protocol utilizes polyethylene glycol (PEG)-conjugated lipids as a generalized approach for incorporating crowders into the supported lipid bilayer&#160;(SLB). First, a cleaning procedure of the microscopic slides and coverslips for performing single-molecule experiments is presented. Next, methods for characterizing the PEG-SLBs and performing single-molecule experiments of the binding, diffusion, and assembly of biomolecules using single-molecule tracking and photobleaching are discussed. Finally, this protocol demonstrates how to monitor the nanopore assembly of bacterial pore-forming toxin Cytolysin A (ClyA) on crowded lipid membranes with single-molecule photobleaching analysis. MATLAB codes with example datasets are also included to perform some of the common analyses such as particle tracking, extracting diffusive behavior, and subunit counting.

Here, a protocol to perform and analyze the binding, mobility, and assembly of single molecules on artificial crowded lipid membranes using single-molecule total internal reflection fluorescence (smTIRF) microscopy is presented.

Cellular membranes are highly crowded environments for biomolecular reactions and signaling. Yet, most in vitro experiments probing protein interaction ...

Assembly of Cell Mimicking Supported and Suspended Lipid Bilayer Models for the Study of Molecular Interactions

Model cell membranes are a useful screening tool with applications ranging from early drug discovery to toxicity studies. The cell membrane is a crucial protective barrier for all cell types, separating the internal cellular components from the extracellular environment. These membranes are composed largely of a lipid bilayer, which contains outer hydrophilic head groups and inner hydrophobic tail groups, along with various proteins and cholesterol. The composition and structure of the lipids themselves play a crucial role in regulating biological function, including interactions between cells and the cellular microenvironment, which may contain pharmaceuticals, biological toxins, and environmental toxicants. In this study, methods to formulate uni-lipid and multi-lipid supported and suspended cell mimicking lipid bilayers are described. Previously, uni-lipid phosphatidylcholine (PC) lipid bilayers as well as multi-lipid placental trophoblast-inspired lipid bilayers were developed for use in understanding molecular interactions. Here, methods for achieving both types of bilayer models will be presented. For cell mimicking multi-lipid bilayers, the desired lipid composition is first determined via lipid extraction from primary cells or cell lines followed by liquid chromatography-mass spectrometry (LC-MS). Using this composition, lipid vesicles are fabricated using a thin-film hydration and extrusion method and their hydrodynamic diameter and zeta potential are characterized. Supported and suspended lipid bilayers can then be formed using quartz crystal microbalance with dissipation monitoring (QCM-D) and on a porous membrane for use in a parallel artificial membrane permeability assay (PAMPA), respectively. The representative results highlight the reproducibility and versatility of in vitro cell membrane lipid bilayer models. The methods presented can aid in rapid, facile assessment of the interaction mechanisms, such as permeation, adsorption, and embedment, of various molecules and macromolecules with a cell membrane, helping in the screening of drug candidates and prediction of potential cellular toxicity.

This protocol describes the formation of cell mimicking uni-lipid and multi-lipid vesicles, supported lipid bilayers, and suspended lipid bilayers. These in vitro models can be adapted to incorporate a variety of lipid types and can be used to investigate various molecule and macromolecule interactions.

Model cell membranes are a useful screening tool with applications ranging from early drug discovery to toxicity studies. The cell membrane is a crucial ...

Reconstitution of Membrane-Tethered Minimal Actin Cortices on Supported Lipid Bilayers

The surface of a living cell provides a versatile active platform for numerous cellular processes, which arise from the interplay of the plasma membrane with the underlying actin cortex. In the past decades, reconstituted, minimal systems based on supported lipid bilayers in combination with actin filament networks have proven to be very instrumental in unraveling basic mechanisms and consequences of membrane-tethered actin networks, as well as in studying the functions of individual membrane-associated proteins. Here, we describe how to reconstitute such active composite systems in vitro that consist of fluid supported lipid bilayers coupled via membrane-associated actin-binding proteins to dynamic actin filaments and myosin motors that can be readily observed via total internal reflection fluorescence microscopy. An open-chamber design allows one to assemble the system in a step-by-step manner and to systematically control many parameters such as linker protein concentration, actin concentration, actin filament length, actin/myosin ratio, as well as ATP levels. Finally, we discuss how to control the quality of the system, how to detect and troubleshoot commonly occurring problems, and some limitations of this system in comparison with the living cell surface.

This protocol describes the formation of supported lipid bilayers and the addition of cytoskeletal filaments and motor proteins to study the dynamics of reconstituted, membrane-tethered cytoskeletal networks using fluorescence microscopy.

The surface of a living cell provides a versatile active platform for numerous cellular processes, which arise from the interplay of the plasma membrane ...

Dissipative Microgravimetry Technique to Study Protein-Lipid Bilayer Interaction

Source: Matos, A. L. L., et al. <a href="https://app.jove.com/v/58224">Dissipative Microgravimetry to Study the Binding Dynamics of the Phospholipid Binding Protein Annexin A2 to Solid-supported Lipid Bilayers Using a Quartz Resonator.</a> J. Vis. Exp. (2018).
This video demonstrates a dissipative microgravimetry technique to investigate the binding of proteins to lipid bilayers. Small unilamellar vesicles are added to coat the surface of the quartz sensor of a microbalance. Utilizing the calcium ion-dependent binding of the target phospholipid-binding protein to the bilayer, changes in the oscillation frequency of the sensor and the dissipation of the oscillation are monitored to determine the nature of the protein-lipid bilayer binding.