electroporation-of-functional-bacterial-effectors-into-mammalian-cells

Electroporation of Functional Bacterial Effectors into Mammalian Cells

The study of protein interactions in the context of living cells can generate critical information about localization, dynamics, and interacting partners. ...

characterization-glycoproteins-with-immunoglobulin-fold-x-ray

Characterization of Glycoproteins with the Immunoglobulin Fold by X-Ray Crystallography and Biophysical Techniques

Glycoproteins on the surface of cells play critical roles in cellular function, including signalling, adhesion and transport. On leukocytes, several of ...

University of Toronto

The Hospital for Sick Children Research Institute

CD22 maintains a baseline level of B-cell inhibition to keep humoral immunity in check. As a B-cell-restricted antigen, CD22 is targeted in therapies against dysregulated B cells that cause autoimmune diseases and blood cancers. Here we report the crystal structure of human CD22 at 2.1 Å resolution, which reveals that specificity for α2-6 sialic acid ligands is dictated by a pre-formed β-hairpin as a unique mode of recognition across sialic acid-binding immunoglobulin-type lectins. The CD22 ectodomain adopts an extended conformation that facilitates concomitant CD22 nanocluster formation on B cells and binding to trans ligands to avert autoimmunity in mammals. We structurally delineate the CD22 site targeted by the therapeutic antibody epratuzumab at 3.1 Å resolution and determine a critical role for CD22 N-linked glycosylation in antibody engagement. Our studies provide molecular insights into mechanisms governing B-cell inhibition and valuable clues for the design of immune modulators in B-cell dysfunction.The B-cell-specific co-receptor CD22 is a therapeutic target for depleting dysregulated B cells. Here the authors structurally characterize the ectodomain of CD22 and present its crystal structure with the bound therapeutic antibody epratuzumab, which gives insights into the mechanism of inhibition of B-cell activation.

Molecular basis of human CD22 function and therapeutic targeting.

Monoclonal antibodies constitute one of the largest groups of drugs to treat cancers and immune disorders, and are guiding the design of vaccines against infectious diseases. Fragments antigen-binding (Fabs) have been preferred over monoclonal antibodies for the structural characterization of antibody-antigen complexes due to their relatively low flexibility. Nonetheless, Fabs often remain challenging to crystallize because of the surface characteristics of complementary determining regions and the residual flexibility in the hinge region between the variable and constant domains. Here, we used a variable heavy-chain (VH) domain specific for the human kappa light chain to assist in the structure determination of three therapeutic Fabs that were recalcitrant to crystallization on their own. We show that this ligand alters the surface properties of the antibody-ligand complex and lowers its aggregation temperature to favor crystallization. The VH crystallization chaperone also restricts the flexible hinge of Fabs to a narrow range of angles, and so independently of the variable region. Our findings contribute a valuable approach to antibody structure determination and provide biophysical insight into the principles that govern the crystallization of macromolecules.

Structural Basis of Enhanced Crystallizability Induced by a Molecular Chaperone for Antibody Antigen-Binding Fragments.

Legionella pneumophila translocates the largest known arsenal of over 330 pathogenic factors, called "effectors," into host cells during infection, enabling L. pneumophila to establish a replicative niche inside diverse amebas and human macrophages. Here, we reveal that the L. pneumophila effectors MavC (Lpg2147) and MvcA (Lpg2148) are structural homologs of cycle inhibiting factor (Cif) effectors and that the adjacent gene, lpg2149, produces a protein that directly inhibits their activity. In contrast to canonical Cifs, both MavC and MvcA contain an insertion domain and deamidate the residue Gln40 of ubiquitin but not Gln40 of NEDD8. MavC and MvcA are functionally diverse, with only MavC interacting with the human E2-conjugating enzyme UBE2N (Ubc13). MavC deamidates the UBE2N∼Ub conjugate, disrupting Lys63 ubiquitination and dampening NF-κB signaling. Combined, our data reveal a molecular mechanism of host manipulation by pathogenic bacteria and highlight the complex regulatory mechanisms integral to L. pneumophila's pathogenic strategy.

Hong Cui

Structural Proteomics Group,
Ontario Center for Structural Proteomics,
Structural Proteomics Group, Ontario Center for Structural Proteomics

University of Toronto

Electroporation of Functional Bacterial Effectors into Mammalian Cells

Characterization of Glycoproteins with the Immunoglobulin Fold by X-Ray Crystallography and Biophysical Techniques

Hong Cui

Structural Proteomics Group,Ontario Center for Structural Proteomics,Structural Proteomics Group, Ontario Center for Structural Proteomics

University of Toronto

Electroporation of Functional Bacterial Effectors into Mammalian Cells

Characterization of Glycoproteins with the Immunoglobulin Fold by X-Ray Crystallography and Biophysical Techniques

Structural Proteomics Group,
Ontario Center for Structural Proteomics,
Structural Proteomics Group, Ontario Center for Structural Proteomics