Hammerschmidt S, Talay S R, Brandtzaeg P, Chhatwal G S
Department of Microbial Pathogenesis, GBF-National Research Centre for Biotechnology, Braunschweig, Germany.
Mol Microbiol. 1997 Sep;25(6):1113-24. doi: 10.1046/j.1365-2958.1997.5391899.x.
The interaction of pathogenic bacteria with host serum and matrix proteins is a common strategy to enhance their virulence. Streptococcus pneumoniae colonizes the human upper respiratory tract in healthy individuals and is also able to cause invasive diseases. Here, we describe a novel pneumococcal surface protein, SpsA, capable of binding specifically to human secretory immunoglobulin A (SIgA). The dissociation constant of SIgA binding to SpsA was 9.3 x 10(-9) M. Free secretory component (SC) also binds to S. pneumoniae, whereas serum IgA does not, suggesting that pneumococcal binding to SIgA is mediated by the SC. To our knowledge, this is the first defined interaction of SC with a prokaryotic protein. The spsA gene encodes a polypeptide of 523 amino acids with a predicted molecular mass of 59 151 Da. The SIgA- or SC-binding domain is located in the N-terminal part of SpsA and exhibits no significant homology to any other proteins. The purified SIgA-binding domain of SpsA could completely inhibit the binding of SIgA to pneumococci. SpsA was expressed by 73% of the tested S. pneumoniae isolates and was substantially conserved between different serotypes. The interaction between S. pneumoniae and SC via SpsA represents a novel biological interaction that might increase virulence by the impairment of bacterial clearance.
病原菌与宿主血清及基质蛋白的相互作用是增强其毒力的常见策略。肺炎链球菌在健康个体的人类上呼吸道中定殖，也能够引发侵袭性疾病。在此，我们描述了一种新型肺炎球菌表面蛋白SpsA，它能够特异性结合人类分泌型免疫球蛋白A（SIgA）。SIgA与SpsA结合的解离常数为9.3×10⁻⁹ M。游离分泌成分（SC）也能与肺炎链球菌结合，而血清IgA则不能，这表明肺炎球菌与SIgA的结合是由SC介导的。据我们所知，这是SC与原核蛋白之间首次明确的相互作用。spsA基因编码一个由523个氨基酸组成的多肽，预测分子量为59151 Da。SIgA或SC结合结构域位于SpsA的N端部分，与任何其他蛋白质均无显著同源性。纯化的SpsA的SIgA结合结构域能够完全抑制SIgA与肺炎球菌的结合。73%的受试肺炎链球菌分离株表达SpsA，且其在不同血清型之间基本保守。肺炎链球菌与SC通过SpsA的相互作用代表了一种新型生物相互作用，可能通过损害细菌清除来增加毒力。
