This OB-fold domain folds into a five-stranded beta-barrel [1]. Members of this family are found in various staphylococcal toxins described as staphylococcal superantigen-like (SSL) proteins that are related to the staphylococcal enterotoxins (SEs) or superantigens. These SSL proteins of which 11 have so far been characterised have a typical SE tertiary structure consisting of a distinct oligonucleotide/oligosaccharide binding (OB-fold), this domain, linked to a beta-grasp domain, family Stap_Strp_tox_C, Pfam:PF02876. SSLs do not bind to T-cell receptors or major histocompatibility complex class II molecules and do not stimulate T cells. SSLs target components of innate immunity, such as complement, Fc receptors, and myeloid cells 2,3,4,5,6,7,8]. SSL protein 7 (SSL7) is the best characterised of the SSLs and binds complement factor C5 and IgA with high affinity and inhibits the end stage of complement activation and IgA binding to FcalphaR [8].

1: The Three-dimensional structure of a superantigen-like protein, SET3, from a pathogenicity island of the Staphylococcus aureus genome. Arcus VL, Langley R, Proft T, Fraser JD, Baker EN; J Biol Chem. 2002;277:32274-32281. PMID:12082105

2: Structural relationships and cellular tropism of staphylococcal superantigen-like proteins. Al-Shangiti AM, Naylor CE, Nair SP, Briggs DC, Henderson B, Chain BM; Infect Immun. 2004;72:4261-4270. PMID:15213171

3: Structural basis for evasion of IgA immunity by Staphylococcus aureus revealed in the complex of SSL7 with Fc of human IgA1. Ramsland PA, Willoughby N, Trist HM, Farrugia W, Hogarth PM, Fraser JD, Wines BD; Proc Natl Acad Sci U S A. 2007;104:15051-15056. PMID:17848512

4: Crystal structures of the staphylococcal toxin SSL5 in complex with sialyl Lewis X reveal a conserved binding site that shares common features with viral and bacterial sialic acid binding proteins. Baker HM, Basu I, Chung MC, Caradoc-Davies T, Fraser JD, Baker EN; J Mol Biol. 2007;374:1298-1308. PMID:17996251

5: The crystal structure of staphylococcal superantigen-like protein 11 in complex with sialyl Lewis X reveals the mechanism for cell binding and immune inhibition. Chung MC, Wines BD, Baker H, Langley RJ, Baker EN, Fraser JD; Mol Microbiol. 2007;66:1342-1355. PMID:18045383

6: Structural basis for inhibition of complement C5 by the SSL7 protein from Staphylococcus aureus. Laursen NS, Gordon N, Hermans S, Lorenz N, Jackson N, Wines B, Spillner E, Christensen JB, Jensen M, Fredslund F, Bjerre M, Sottrup-Jensen L, Fraser JD, Andersen GR; Proc Natl Acad Sci U S A. 2010;107:3681-3686. PMID:20133685

7: Substrate recognition by complement convertases revealed in the C5-cobra venom factor complex. Laursen NS, Andersen KR, Braren I, Spillner E, Sottrup-Jensen L, Andersen GR; EMBO J. 2011;30:606-616. PMID:21217642

8: Structural and functional properties of staphylococcal superantigen-like protein\t4. Hermans SJ, Baker HM, Sequeira RP, Langley RJ, Baker EN, Fraser JD; Infect Immun. 2012;80:4004-4013. PMID:22949551