The thermophilic anaerobic Gram-positive bacterium Carboxydothermus ferrireducens utilizes insoluble Fe(III) oxides as electron acceptors in respiratory processes using an extracellular 11-heme cytochrome c OmhA as a terminal reductase. OmhA is able to transfer electrons to soluble and insoluble Fe(III) compounds, substrates of multiheme oxidoreductases, and soluble electron shuttles. The crystal structure of OmhA at 2.5 Å resolution shows that it consists of two functionally distinct parts: the cytochrome с electron transfer and the S-layer binding domains. Nonaheme C-terminal subdomain of the cytochrome с domain is structurally similar to the extracellular multiheme cytochrome OcwA from the metal-reducing Gram-positive bacterium “Thermincola potens.” S-layer binding domain of OmhA is responsible for interaction with the S-layer that surrounds the Carboxydothermus ferrireducens cell envelope. The structural foundations enabling the embedding of extracellular multiheme cytochromes to the S-layer of a Gram-positive-type cell wall and putative electron transfer pathways to insoluble minerals are discussed.

嗜热厌氧革兰氏阳性细菌Carboxydothermus ferrireducens利用不溶性 Fe(III) 氧化物作为呼吸过程中的电子受体，使用细胞外 11-血红素细胞色素c  OmhA 作为末端还原酶。OmhA 能够将电子转移到可溶性和不溶性 Fe(III) 化合物、多血红素氧化还原酶的底物和可溶性电子穿梭机。OmhA 在 2.5 Å 分辨率下的晶体结构表明它由两个功能不同的部分组成：细胞色素с电子转移和S层结合域。细胞色素с的九血红素 C 端子域域在结构上类似于来自金属还原革兰氏阳性细菌“ Thermincola potens ”的细胞外多血红素细胞色素 OcwA。OmhA 的S层结合域负责与Carboxydothermus ferrireducens细胞包膜周围的S层相互作用。讨论了能够将细胞外多血红素细胞色素嵌入革兰氏阳性细胞壁S层的结构基础和不溶性矿物质的推定电子转移途径。