科研之友
微信
新浪微博
Facebook
分享链接
摘要
A emm53 subclass of Group A Streptococcus pyogenes (GAS) interacts tightly with human plasma plasminogen (hPg) and plasmin (hPm) via the kringle 2 (K2(hPg)) domain of hPg/hPm and the N-terminal a1a2 regions of a GAS coiled-coil M-like protein (PAM). Previous studies have shown that a monomeric PAM fragment, VEK30 (residues 97-125 + Tyr), interacted specifically with isolated K2(hPg). However, the binding strength of VEK30 (K-D = 56 nM) was similar to 60-fold weaker than that of full-length dimeric PAM (K-D = 1nM). To assess whether this attenuated binding was due to the inability of VEK30 to dimerize, we defined the minimal length of PAM required to dimerize using a series of peptides with additional PAM residues placed at the NH2 and COOH termini of VEK30.VEK64 (PAM residues 83-145 + Tyr) was found to be the smallest peptide that adopted an alpha-helical dimer, and was bound to K2(hPg) with nearly the same affinity as PAM (K-D = 1-2 nM). However, addition of two PAM residues (Arg(126)-His(127)) to the COOH terminus of VEK30 (VEK32) maintained a monomeric peptidic structure, but exhibited similar K2(hPg) binding affinity as full-length dimeric PAM. We identified five residues in a1a2 (Arg(113), His(114), Glu(116), Arg(126), His(127)), mutation of which reduced PAM binding affinity for K2(hPg) by similar to 1000-fold. Replacement of these critical residues by Ala in the GAS genome resulted in reduced virulence, similar to the effects of inactivating the PAM gene entirely. We conclude that rather than dimerization of PAM, the five key residues in the binding domain of PAM are essential to mediate the high affinity interaction with hPg, leading to increased GAS virulence.
- 出版日期2014-8-1
