Iron-containing lipoprotein SiaA in SiaABC, the primary heme transporter of Streptococcus pyogenes
Iron-containing lipoprotein SiaA in SiaABC, the primary heme transporter of Streptococcus pyogenes
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DOI：
10.1007/s00775-010-0684-4
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发表时间：
2010-07
期刊：
影响因子：
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通讯作者：
Xuesong Sun;R. Ge;Dongmei Zhang;Hongzhe Sun;Qing‐Yu He
中科院分区：
文献类型：
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作者：
Xuesong Sun;R. Ge;Dongmei Zhang;Hongzhe Sun;Qing‐Yu He
细胞表面脂蛋白SiaA是SiaABC转运蛋白的一个组成部分，在臭名昭著的人类病原体化脓性链球菌中充当血红素的主要受体。然而，很少有人知道血红素结合和释放的分子机制，以及血红素结合配体的作用，有助于摄取血红素进入致病菌。本报告旨在阐明SiaA中血红素铁的配位性质。与野生型SiaA蛋白相比，通过用丙氨酸取代Met79或His229，突变体M79A和H229A蛋白显示出显著降低的血红素结合亲和力和显著增加的血红素释放速率。荧光光谱和圆二色光谱表明，血红素结合的结果在蛋白质的二级结构的改变。血红素从SiaA的释放是一个逐步的过程，其中血红素首先从Met 79解离，然后从His229解离，具有明显的构象变化。His229可以作为血红素结合在SiaA中的锚，并且因此可以在血红素和蛋白质之间的配位的稳定性中发挥主要作用。
The cell-surface lipoprotein SiaA, a component of the SiaABC transporter, acts as the primary receptor for heme in the infamous human pathogen Streptococcus pyogenes. However, little is known about the molecular mechanism of heme binding and release as well as the role of heme-binding ligands that contribute to the uptake of heme into the pathogenic bacteria. The present report aims to clarify the coordination properties of heme iron in SiaA. By substitution of either Met79 or His229 with alanine, the mutant M79A and H229A proteins display significantly decreased heme-binding affinity and substantially increased heme-release rates, as compared with wild-type SiaA protein. Both fluorescence and circular dichroism spectra indicated that heme binding results in alterations in the secondary structure of the protein. Heme release from SiaA is a stepwise process in which heme dissociates firstly from Met79 and then from His229 with distinct conformational changes. His229 may serve as an anchor for heme binding in SiaA and thus may play a major role in the stability of the coordination between heme and the protein.