Lee B C, Hill P
Department of Microbiology and Infectious Diseases, University of Calgary, Canada.
J Gen Microbiol. 1992 Dec;138(12):2647-56. doi: 10.1099/00221287-138-12-2647.
Although Neisseria meningitidis can use haemoglobin as an iron source in vitro, the mechanism of haemoglobin-iron uptake is unknown. Using a biotinylated human haemoglobin probe in a solid-phase dot-binding assay, haemoglobin-binding activity was detected in total membranes derived from meningococci grown under iron-limited but not iron-sufficient conditions. In competition binding experiments, bovine and human haemoglobin could abrogate binding. In contrast, no binding inhibition was seen with ferric nitrate, protoporphyrin IX, and iron-loaded human transferrin. The ability of both haemin and catalase, a nonhaemoglobin haem-containing compound, to inhibit binding competitively suggested that the ligand recognized by the binding protein is the haem moiety. Scatchard plot analysis revealed a heterogeneous receptor population. Limited proteolysis with proteinase K abolished binding activity, suggesting a haemoglobin-protein interaction. Detection of activity in a whole-cell binding assay demonstrated that this haemin-binding protein was surface exposed. In a limited survey of meningococcal strains, the presence of haemoglobin-binding activity in all isolates indicated that expression of this binding protein is not serogroup specific.
虽然脑膜炎奈瑟菌在体外可利用血红蛋白作为铁源，但血红蛋白-铁摄取机制尚不清楚。在固相点结合试验中使用生物素化人血红蛋白探针，在铁限制而非铁充足条件下生长的脑膜炎球菌的总膜中检测到血红蛋白结合活性。在竞争结合实验中，牛血红蛋白和人血红蛋白可消除结合。相反，硝酸铁、原卟啉IX和铁负载的人转铁蛋白未见结合抑制。血红素和过氧化氢酶（一种不含血红蛋白的含血红素化合物）竞争性抑制结合的能力表明，结合蛋白识别的配体是血红素部分。Scatchard图分析显示受体群体具有异质性。用蛋白酶K进行有限的蛋白水解消除了结合活性，提示存在血红蛋白-蛋白质相互作用。全细胞结合试验中活性的检测表明，这种血红素结合蛋白暴露于表面。在对脑膜炎球菌菌株的有限调查中，所有分离株中均存在血红蛋白结合活性，表明该结合蛋白的表达不具有血清群特异性。
