The CcmC:Heme:CcmE Complex in Heme Trafficking and Cytochrome c Biosynthesis
The CcmC:Heme:CcmE Complex in Heme Trafficking and Cytochrome c Biosynthesis
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DOI：
10.1016/j.jmb.2010.06.041
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发表时间：
2010-08-20
影响因子：
5.6
通讯作者：
Kranz, Robert G.
中科院分区：
文献类型：
--
作者：
Richard-Fogal, Cynthia;Kranz, Robert G.
整合膜蛋白超家族的特征在于在内膜表面的外环中的保守的富含色氨酸的区域（称为WWD结构域）。该家族的三个主要成员（CcmC、CcmF和CcsBA）均参与细胞色素c的生物合成，但WWD结构域的功能尚不清楚。已经假设WWD结构域结合血红素以将其呈递给受体蛋白（对于CcmC为apoCcmE或对于CcmF和CcsBA为apo细胞色素c），使得血红素乙烯基共价连接到受体。替代方案表明WWWD结构域直接与受体蛋白相互作用（例如，apoCcmE用于CcmC）。在这里，它表明，CcmC仅被困与血红素时，其同源受体蛋白CcmE存在。它表明，CcmE只有在血红素存在时才能与CcmC稳定地相互作用;因此，每个蛋白质中的特定残基提供与血红素相互作用的位点，以形成这种非常稳定的复合物。第一次，证据表明，外部WWWD域的CcmC直接与血红素相互作用。CcmC的WWD结构域中完全保守的残基的单个和多个取代改变了血红素在稳定的CcmC：血红素：CcmE复合物中的光谱性质。此外，一些突变使血红素的结合降低至100%。内源性合成的血红素很可能通过这种六跨膜蛋白内的通道或从膜进入CcmC的外部WWD结构域。数据表明，特定的血红素通道（即，跨膜螺旋内的血红素结合位点）不存在于CcmC中，与CcsBA蛋白相反。我们讨论的可能性，它是不重要的，以保护血红素通过贩运CcmC，而它是至关重要的CcsBA。(C)2010爱思唯尔有限公司版权所有。
A superfamily of integral membrane proteins is characterized by a conserved tryptophan-rich region (called the WWD domain) in an external loop at the inner membrane surface. The three major members of this family (CcmC, CcmF, and CcsBA) are each involved in cytochrome c biosynthesis, yet the function of the WWD domain is unknown. It has been hypothesized that the WWD domain binds heme to present it to an acceptor protein (apoCcmE for CcmC or apocytochrome c for CcmF and CcsBA) such that the heme vinyl group(s) covalently attaches to the acceptors. Alternative proposals suggest that the WWWD domain interacts directly with the acceptor protein (e.g., apoCcmE for CcmC). Here, it is shown that CcmC is only trapped with heme when its cognate acceptor protein CcmE is present. It is demonstrated that CcmE only interacts stably with CcmC when heme is present; thus, specific residues in each protein provide sites of interaction with heme to form this very stable complex. For the first time, evidence that the external WWWD domain of CcmC interacts directly with heme is presented. Single and multiple substitutions of completely conserved residues in the WWD domain of CcmC alter the spectral properties of heme in the stable CcmC:heme:CcmE complexes. Moreover, some mutations reduce the binding of heme up to 100%. It is likely that endogenously synthesized heme enters the external WWD domain of CcmC either via a channel within this six-transmembrane-spanning protein or from the membrane. The data suggest that a specific heme channel (i.e., heme binding site within membrane spanning helices) is not present in CcmC, in contrast to the CcsBA protein. We discuss the likelihood that it is not important to protect the heme via trafficking in CcmC whereas it is critical in CcsBA. (C) 2010 Elsevier Ltd. All rights reserved.