The crystal structure of staphylococcal superantigen-like protein 11 in complex with sialyl Lewis X reveals the mechanism for cell binding and immune inhibition.
Staphylococcus aureus is a major pathogen that produces a family of 14 staphylococcal superantigen-like (SSL) proteins, which are structurally similar to superantigens but do not stimulate T cells. SSL11 is one member of the family that is found in all staphylococcal strains. Recombinant SSL11 bound to granulocytes and monocytes through a sialic acid-dependent mechanism and was rapidly internalized. SSL11 also bound to sialic acid-containing glycoproteins, such as the Fc receptor for IgA (FcalphaRI) and P-selectin glycoprotein ligand-1 (PSGL-1), and inhibited neutrophil attachment to a P-selectin-coated surface. Biosensor analysis of two SSL11 alleles binding to sialyl Lewis X [sLe(x)- Neu5Acalpha2-3Galbeta1-4(Fuc1-3)GlcNAc] coupled to bovine serum albumin gave dissociation constants of 0.7 and 7 mum respectively. Binding of SSL11 to a glycan array revealed specificity for glycans containing the trisaccharide sialyllactosamine (sLacNac - Neu5Acalpha2-3Galbeta1-4GlcNAc). A 1.6 A resolution crystal structure of SSL11 complexed with sLe(x) revealed a discrete binding site in the C-terminal beta-grasp domain, with predominant interactions with the sialic acid and galactose residues. A single amino acid mutation in the carbohydrate binding site abolished all SSL11 binding. Thus, SSL11 is a staphylococcal protein that targets myeloid cells by binding sialyllactosamine-containing glycoproteins.
Maurice Wilkins Centre, University of Auckland, Auckland, New Zealand.
Matthew C
MC
Chung
Bruce D
BD
Wines
Heather
H
Baker
Ries J
RJ
Langley
Edward N
EN
Baker
John D
JD
Fraser
D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D015153:Blotting, Western; D018360:Crystallography, X-Ray / Q000379:methods; D005434:Flow Cytometry; D006098:Granulocytes / Q000378:metabolism; D006801:Humans; D007070:Immunoglobulin A / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009000:Monocytes / Q000378:metabolism; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D009504:Neutrophils / Q000382:microbiology; D019007:P-Selectin / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011961:Receptors, Fc / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013211:Staphylococcus aureus / Q000235:genetics / Q000378:metabolism*; D018089:Superantigens / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D020349:Surface Plasmon Resonance
D001426:Bacterial Proteins; D007070:Immunoglobulin A; D008562:Membrane Glycoproteins; D019007:P-Selectin; C084882:P-selectin ligand protein; D011961:Receptors, Fc; D011994:Recombinant Proteins; D018089:Superantigens; D019158:N-Acetylneuraminic Acid