The covalent attachment of one or multiple heme cofactors to cytochrome c protein chains enables cytochrome c proteins to be used in electron transfer and redox catalysis in extracytoplasmic environments. A dedicated heme maturation machinery, whose core component is a heme lyase, scans nascent peptides after Sec-dependent translocation for CX_nCH-binding motifs. Here we report the three-dimensional (3D) structure of the heme lyase CcmF, a 643-amino acid integral membrane protein, from Thermus thermophilus. CcmF contains a heme b cofactor at the bottom of a large cavity that opens toward the extracellular side to receive heme groups from the heme chaperone CcmE for cytochrome maturation. A surface groove on CcmF may guide the extended apoprotein to heme attachment at or near a loop containing the functionally essential WXWD motif, which is situated above the putative cofactor binding pocket. The structure suggests heme delivery from within the membrane, redefining the role of the chaperone CcmE.

一种或多种血红素辅助因子与细胞色素c蛋白链的共价结合使细胞色素c蛋白能够用于胞质外环境中的电子转移和氧化还原催化。_{一种专用的血红素成熟机制，其核心成分是血红素裂解酶，在 CX n} CH 结合基序的Sec 依赖性易位后扫描新生肽。在这里，我们报告了血红素裂解酶 CcmF 的三维 (3D) 结构，这是一种来自Thermus thermophilus的 643 氨基酸整合膜蛋白。CcmF 含有血红素b大空腔底部的辅助因子，该空腔向细胞外侧开放，以接收来自血红素伴侣 CcmE 的血红素基团，用于细胞色素成熟。CcmF 上的表面凹槽可以引导扩展的载脂蛋白连接到包含功能必需的 WXWD 基序的环处或附近的血红素附着，该基序位于假定的辅因子结合口袋上方。该结构表明血红素从膜内递送，重新定义伴侣 CcmE 的作用。