Crystal structure of a staphylokinase: variant a model for reduced antigenicity.
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.
Chen
Yuhang
Y
Laboratory of Structural Biology, MOE Laboratory of Protein Science, Tsinghua University, Beijing, China.
Song
Gang
G
Jiang
Fan
F
Feng
Liang
L
Zhang
Xiaoxuan
X
Ding
Yi
Y
Bartlam
Mark
M
Yang
Ao
A
Ma
Xiang
X
Ye
Sheng
S
Liu
Yiwei
Y
Tang
Hong
H
Song
Houyan
H
Rao
Zihe
Z
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
D000942:Antigens, Bacterial; D008666:Metalloendopeptidases; C022653:auR protein, Staphylococcus aureus