title: Crystal structure of a staphylokinase: variant a model for reduced antigenicity.
abstract: Staphylokinase (SAK) is a 15.5-kDa protein from Staphylococcus aureus that activates plasminogen by forming a 1 : 1 complex with plasmin. Recombinant SAK has been shown in clinical trials to induce fibrin-specific clot lysis in patients with acute myocardial infarction. However, SAK elicits high titers of neutralizing antibodies. Biochemical and protein engineering studies have demonstrated the feasibility of generating SAK variants with reduced antigenicity yet intact thrombolytic potency. Here, we present X-ray crystallographic evidence that the SAK(S41G) mutant may assume a dimeric structure. This dimer model, at 2.3-A resolution, could explain a major antigenic epitope (residues A72-F76 and residues K135-K136) located in the vicinity of the dimer interface as identified by phage-display. These results suggest that SAK antigenicity may be reduced by eliminating dimer formation. We propose several potential mutation sites at the dimer interface that may further reduce the antigenicity of SAK.
authors.affiliation: Laboratory of Structural Biology, MOE Laboratory of Protein Science, Tsinghua University, Beijing, China.
authors.forename: Yuhang
authors.initials: Y
authors.lastname: Chen
authors.forename: Gang
authors.initials: G
authors.lastname: Song
authors.forename: Fan
authors.initials: F
authors.lastname: Jiang
authors.forename: Liang
authors.initials: L
authors.lastname: Feng
authors.forename: Xiaoxuan
authors.initials: X
authors.lastname: Zhang
authors.forename: Yi
authors.initials: Y
authors.lastname: Ding
authors.forename: Mark
authors.initials: M
authors.lastname: Bartlam
authors.forename: Ao
authors.initials: A
authors.lastname: Yang
authors.forename: Xiang
authors.initials: X
authors.lastname: Ma
authors.forename: Sheng
authors.initials: S
authors.lastname: Ye
authors.forename: Yiwei
authors.initials: Y
authors.lastname: Liu
authors.forename: Hong
authors.initials: H
authors.lastname: Tang
authors.forename: Houyan
authors.initials: H
authors.lastname: Song
authors.forename: Zihe
authors.initials: Z
authors.lastname: Rao
mesh_terms: D000942:Antigens, Bacterial / Q000737:chemistry* / Q000276:immunology; D018360:Crystallography, X-Ray; D019281:Dimerization; D004591:Electrophoresis, Polyacrylamide Gel; D008666:Metalloendopeptidases / Q000737:chemistry* / Q000276:immunology; D008958:Models, Molecular; D009500:Neutralization Tests
chemical_list: D000942:Antigens, Bacterial; D008666:Metalloendopeptidases; C022653:auR protein, Staphylococcus aureus