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HxuA 介导的血红素从血红素结合蛋白中的释放使流感嗜血杆菌能够逃避宿主的营养免疫。

Haem release from haemopexin by HxuA allows Haemophilus influenzae to escape host nutritional immunity.

机构信息

Unité des Membranes Bactériennes, CNRS URA 2172, Département de Microbiologie, Institut Pasteur, 25 rue du Dr Roux, 75724 Paris Cedex 15, France.

出版信息

Mol Microbiol. 2011 Apr;80(1):133-48. doi: 10.1111/j.1365-2958.2011.07562.x. Epub 2011 Feb 15.

Abstract

Haemophilus influenzae is an obligate human commensal/pathogen. This haem auxotroph must acquire haem from its host to sustain aerobic growth. Haem-haemopexin complexes are one of the potential sources of haem for this microorganism. Haemopexin is a glycoprotein that binds haem with high affinity (subpicomolar Kd) and involved in haem recycling. HxuA, a cell surface protein, is the key to haem acquisition from haemopexin. In this study, we reconstituted a functional Hxu system from H. influenzae in Escherichia coli K-12 that mediated active haem transport across the outer membrane from haem-haemopexin, in the presence of the inner membrane energy-transducing TonB-ExbB-ExbD complex from H. influenzae. A secreted variant of HxuA, HxuA(dm), was produced in E. coli. HxuA(dm) functionally complemented an hxuA mutant of H. influenzae for haem-haemopexin acquisition. HxuA(dm) interacted with haemopexin and haem-haemopexin, with which it formed high-affinity, stoichiometric complexes. Following the interaction between haem-haemopexin and HxuA(dm), haem was no longer bound to its initial high-affinity site and became accessible to its cognate haem receptor, HxuC. HxuA(dm) and the HxuA(dm)-haemopexin complex do not appear to bind haem at detectable levels (affinities below 10(6) M(-1)). HxuA thus appears to 'release' haem from haem-haemopexin complexes and to prevent haem sequestering by haemopexin.

摘要

流感嗜血杆菌是一种专性人共生/病原体。这种血红素营养缺陷型必须从宿主中获取血红素以维持需氧生长。血红素-结合珠蛋白复合物是该微生物血红素的潜在来源之一。结合珠蛋白是一种糖蛋白,与血红素有高亲和力(亚皮摩尔 Kd)结合,并参与血红素循环利用。细胞表面蛋白 HxuA 是从结合珠蛋白中获取血红素的关键。在这项研究中,我们在大肠杆菌 K-12 中重建了具有功能的 Hxu 系统,该系统介导了来自血红素-结合珠蛋白的活性血红素跨外膜转运,同时存在来自流感嗜血杆菌的内膜能量转导 TonB-ExbB-ExbD 复合物。HxuA 的分泌变体 HxuA(dm)在大肠杆菌中产生。HxuA(dm)在功能上补充了流感嗜血杆菌 hxuA 突变体的血红素-结合珠蛋白获取。HxuA(dm)与结合珠蛋白和血红素-结合珠蛋白相互作用,形成高亲和力、化学计量比的复合物。在血红素-结合珠蛋白与 HxuA(dm)相互作用后,血红素不再与最初的高亲和力位点结合,并且可以与同源血红素受体 HxuC 结合。HxuA(dm)和 HxuA(dm)-结合珠蛋白复合物似乎不以可检测水平(亲和力低于 10(6) M(-1))结合血红素。因此,HxuA 似乎可以从血红素-结合珠蛋白复合物中“释放”血红素,并防止结合珠蛋白对血红素的隔离。

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