We express our sincere appreciation for the financial support received from the Connotation Construction Project of the 14th Five-Year Plan of the University of Tibetan Medicine (2022ZYYGH12), the 2022 Open Subjects of the Key Laboratory of Tibetan Medicine and Basic Education of the Ministry of Education at the University of Tibetan Medicine (ZYYJC-22-04), the Key Research and Development Program of Ningxia (2023BEG02012), and the Xinglin Scholar Research Promotion Project of Chengdu University of Traditional Chinese Medicine (XKTD2022013).

The compound solution, protein solution, and dye were introduced into a PBS solution. Subsequently, the samples underwent gradual heating using a digital heating shaking dry bath, and the thermal stability of the proteins was evaluated by measuring the change in fluorescence intensity within the complex system. The detailed steps are outlined below, and Figure 1 illustrates an overview of the protocol.
1. Solution preparation
<ol>
	<li>Prepare a...

High-Sensitivity Detection of Compound-Protein Binding Using Fluorescence

<ol>
	<li>Cairang, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Study+on+the+standardization+of+clinical+application+of+Tibetan+medicine+&amp;#34;five+roots&amp;#34.">Study on the standardization of clinical application of Tibetan medicine &amp;#34;five roots&amp;#34.</a> Guid J Trad Chin Med Pharm. 28 (11), 133136 (2022).</li><li>Li, L., 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=Effects+of+Xigui+extract+on+immunosuppressive+mice+induced+by+cyclophosphamide.">Effects of Xigui extract on immunosuppressive mice induced by cyclophosphamide.</a> Chin J Hosp Pharm. 37 (03), 244-247 (2017).</li><li>Lu, H., 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=Effects+of+Vicatia+thibertica+de+boiss+on+immunologic+and+hematopoietic+function+of+mice.">Effects of Vicatia thibertica de boiss on immunologic and hematopoietic function of mice.</a> J Dali Univ. 2 (02), 6-10 (2017).</li><li>Dong, S., Zhang, X., Hu, Y., Gong, X., Yang, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+constituents,+quality+control+and+pharmacology+research+progress+of+Xigui.">Chemical constituents, quality control and pharmacology research progress of Xigui.</a> Chin J Ethnomed Ethnopharm. 27 (13), 40-42 (2018).</li><li>Lu, Z., Zhang, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+total+flavone+extract+from+Shuiqin+(Oenanthe+Javanica)+on+immune+function+of+immunosuppression+mice.">Effects of total flavone extract from Shuiqin (Oenanthe Javanica) on immune function of immunosuppression mice.</a> Chin J Trad Med Sci Technol. 23 (04), 423-425 (2016).</li><li>Vonderheide, R. 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The authors have nothing to disclose.

DSF, also known as the thermal shift assay or thermal fluorescence assay, is a technique employed to detect the process of thermal denaturation of proteins in samples by monitoring changes in the fluorescence signal of the test sample or dye during a slow, programmed temperature increase. Initially established by Pantoliano14, DSF serves as a high-throughput method. The main procedure involves elevating the temperature on a computer-controlled heated plate, emitting excitation light using a long-w...

Vicatia thibetica H. Boissieu, a plant in the umbelliferous family, is commonly used in Tibetan medicine and represents one of the essential components of the five basic ingredients (Polygonatum sibiricum Delar. ex Redoute, Asparagus cochinchinensis (Lour.) Merr, Vicatia thibetica H. Boissieu, Oxybaphus himalaicus Edgew., and Gymnadenia conopsea (L.) R. Br.)1. Mainly distributed in southwest China, such as northwest Yunnan, western Sichuan, Tibet, and other areas, its dried root serves as a local substitute for Angelica1. The root, known for its fragrance, is often utilized as a stew seasoning, and the leaves, referred to as Tibetan celery, contribute to delectable dishes. Thus, Vicatia thibetica holds significance not only as a unique medicinal plant but also as a food source in Tibet.
Both domestic and international research indicates that Vicatia thibetica possesses blood-replenishing and qi (power or energy)-invigorating properties, beneficial for regulating menstruation. It is employed to address symptoms of irregular menstrual dysmenorrhea caused by palpitation and blood deficiency, exhibiting pharmacological effects such as antioxidant regulation of body immunity2. The alcohol extract of Vicatia thibetica has demonstrated the ability to restore body mass and organ index in immunocompromised mice induced by cyclophosphamide. Additionally, it increases the activity of superoxide dismutase in serum and reduces the content of malondialdehyde, suggesting an improvement in antioxidant capacity and a balancing effect on lipid peroxidation2,3. Simultaneously, it enhances the number of blood cells and hemoglobin, which not only objectively reflects the body&#39;s hematopoietic function but also plays a crucial role in the immune system2,3.
Umbelliferone, characterized by acicular crystals and a bitter taste, possesses a small molecular weight, is volatile, and can be distilled with steam. It sublimates easily, has low solubility in water, and high solubility in organic matter. As one of the main chemical components of Vicatia thibetica, umbelliferone exhibits immunomodulatory effects on cellular immunity, humoral immunity, and non-specific immunity in hydrocortisone-induced immunosuppression mouse models4,5.
The cell surface molecule CD40, a member of the tumor necrosis factor receptor superfamily, is widely expressed in immune cells6. Its homologous ligand, CD154, also known as CD40L, is a type II transmembrane protein expressed by activated T lymphocytes. CD40 activation has the capacity to up-regulate the expression of co-stimulatory molecules on the surface of dendritic cells (DC) and monocytes. This process promotes the antigen presentation function of major histocompatibility complex (MHC) molecules and further activates CD8+ T cells7.
Macrophages play a crucial role in the formation and regulation of the tumor microenvironment, and CD40 activation can enhance the remodeling of the tumor microenvironment by macrophages8. CD40 signal activation significantly influences the proliferation and activation of B cells. B cells, when activated by CD40, can function as effective antigen-presenting cells. They present antigens, generate effector T cell activity, and thereby contribute to anti-tumor effects9. Moreover, CD40 activation in tumor cells can induce apoptosis and inhibit tumor growth10. CD40 primarily transduces signals by controlling the activity of non-receptor tyrosine protein kinases, including Lyn, Fyn, Syk, and others. Additionally, it has the ability to stimulate Bcl-xL, Cdk4, and Cdk6 proteins, activate Rel/NF-kB transcription factors, and phosphorylate CG-2 and PI3K10.
The Differential Scanning Fluorescence (DSF) method is widely employed to assess the impact of various environmental conditions, such as buffer composition, temperature, and small molecule ligands, on the thermal stability of protein structures. The commonly utilized dye for DSF is an orange, environmentally sensitive, hydrophobic dye. Under normal conditions, the protein structure is folded, concealing its hydrophobic segment internally. As the temperature increases, the protein&#39;s hydrophobic region becomes more exposed, resulting in a gradual breakdown of the natural protein structure. The dye selectively binds to this exposed protein portion, amplifying its fluorescence. Tm values are then calculated by monitoring changes in the fluorescence signal detection11. To a certain extent, variations in Tm values can gauge shifts in protein stability due to mutations, changes in buffers, or ligand binding. Furthermore, it can indicate structural alterations during the protein folding process12. This approach offers precise data, a broad temperature range, high sensitivity, and minimal protein sample loss13.
In this study, fluorescence determination was conducted using a fluorescent microplate reader instead of a fluorescence quantitative polymerase chain reaction (PCR) apparatus. This modification enables DSF detection in laboratories lacking a fluorescent quantitative PCR instrument, making the method less complex and reducing the steps required for instrument setup, thereby simplifying the experimental process. However, there are certain drawbacks to this approach. While the complexity is reduced, the procedure becomes more cumbersome. Manual fluorescence detection at different temperatures is necessary, and automatic and continuous collection of fluorescence from the system cannot be achieved. Thus, this study utilized the DSF technique to explore the interaction between CD40 protein and umbelliferone, providing novel insights into the molecular mechanisms of Tibetan medicine.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>CD40 protein</td>
			<td>MedChemExpress</td>
			<td>HY-P75408</td>
			<td></td>
		</tr>
		<tr>
			<td>DMSO</td>
			<td>Boster Biological Technology Co., Ltd</td>
			<td>PYG0040</td>
			<td></td>
		</tr>
		<tr>
			<td>FlexStation 3 multifunctional microplate reader</td>
			<td>Shanghai Meigu Molecular Instruments Co., LTD</td>
			<td>FlexStation 3</td>
			<td></td>
		</tr>
		<tr>
			<td>OriginPro 8 software</td>
			<td>OriginLab Corporation</td>
			<td>v8.0724(B724)</td>
			<td></td>
		</tr>
		<tr>
			<td>Phosphate buffered saline (1x)</td>
			<td>Gibco</td>
			<td>8120485</td>
			<td></td>
		</tr>
		<tr>
			<td>SoftMax Pro 7.1</td>
			<td>Shanghai Meigu Molecular Instruments Co., LTD</td>
			<td>SoftMax Pro 7.1</td>
			<td></td>
		</tr>
		<tr>
			<td>SSYPRO orange dye</td>
			<td>Sigma</td>
			<td>S5942</td>
			<td></td>
		</tr>
		<tr>
			<td>Umbelliferone</td>
			<td>Shanghai Yuanye Biotechnology Co.</td>
			<td>B21854</td>
			<td></td>
		</tr>
	</tbody>
</table>

detection of cd40 protein-umbelliferone interaction via differential scanning fluorescence

The investigation of interactions between different molecules is a crucial aspect of understanding disease pathogenesis and screening for drug targets. Umbelliferone, an active ingredient in Tibetan medicine Vicatia thibetica, exhibits an immunomodulatory effect with an unknown mechanism. The CD40 protein is a key target in the immune response. Therefore, this study employs the principle of differential scanning fluorescence technology to analyze the interactions between CD40 protein and umbelliferone using fluorescent enzyme markers. Initially, the stability of the protein fluorescent orange dye was experimentally verified, and the optimal dilution ratio of 1:500 was determined. Subsequently, it was observed that the temperature melting (Tm) value of CD40 protein tended to decrease with an increase in concentration. Interestingly, the interaction between CD40 protein and umbelliferone was found to enhance the thermal stability of CD40 protein. This study represents the first attempt to detect the binding potential of small molecule compounds and proteins using fluorescence microplates and fluorescent dyes. The technique is characterized by high sensitivity and accuracy, promising advancements in the fields of protein stability, protein structure, and protein-ligand interactions, thus facilitating further research and exploration.

Author Spotlight: Streamlining PCR Methods for Enhanced Accessibility and Efficiency

Detection of CD40 Protein-Umbelliferone Interaction via Differential Scanning Fluorescence

Our protocol provides a significant advantage by allowing use without specialized equipment. Unlike traditional fluorescence quantitative PCR methods, it simplifies the experimental process, requiring fewer steps and reducing overall complexity, making it safer and easier to conduct. This experiment requires the operator to be very familiar with the experimental procedure and the fluorescent microplate reader, and not to waste too much time during the solution heating and the fluorescence detection.We will focus on the molecular mechanism by which umbelliferone binds to CD14 protein to produce immune effects.

The orange dye consistently exhibited stable fluorescence excitation at Ex = 470 nm and Em = 570 nm, both at room temperature and elevated temperatures. An optimal dilution ratio of 1:500 was determined (Figure 2A,B). Detection of the Tm value proved challenging when the concentration of CD40 protein was below 15 &#181;g/mL (Figure 3A,B). However, at a concentration of 15 &#181;g/mL, a stable Tm value of 51.82 &#176;C was detec...

Watch this Scientific Journal Video about Author Spotlight: Streamlining PCR Methods for Enhanced Accessibility and Efficiency at JoVE.com

This protocol describes a unique method for detecting the binding between compounds and protein molecules, offering the advantages of minimal protein sample loss and high data accuracy.

The investigation of interactions between different molecules is a crucial aspect of understanding disease pathogenesis and screening for drug targets. ...

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Determination of CD40 Protein-Umbelliferone Compound Interaction Using Differential Fluorescence Scanning

348 Views.  University of Tibetan Medicine.  This protocol describes a unique method for detecting the binding between compounds and protein molecules, offering the advantages of minimal protein sample loss and high data accuracy.

High-Sensitivity Detection of Compound-Protein Binding Using Fluorescence

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