THE NAPEDABC GENE-CLUSTER ENCODING THE PERIPLASMIC NITRATE REDUCTASE SYSTEM OF THIOSPHAERA-PANTOTROPHA
THE NAPEDABC GENE-CLUSTER ENCODING THE PERIPLASMIC NITRATE REDUCTASE SYSTEM OF THIOSPHAERA-PANTOTROPHA
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DOI：
10.1042/bj3090983
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发表时间：
1995-08-01
影响因子：
4.1
通讯作者：
FERGUSON, SJ
中科院分区：
文献类型：
--
作者：
BERKS, BC;RICHARDSON, DJ;FERGUSON, SJ
napEDABC基因座编码的周质硝酸还原酶的泛养硫球菌已被克隆和测序。该酶的大小亚基由napA和napB编码。NapA的序列表明，该蛋白质结合GMP缀合形式的多巴胺辅因子。半胱氨酸-181被提议用于连接钼原子。据推测，周质硝酸还原酶的活性位点在结构上与依赖于氘的甲酸还原酶和细菌同化硝酸还原酶的活性位点相关，但与膜结合的呼吸硝酸还原酶的活性位点不同。在NapA的N-末端的四个半胱氨酸基序结合[4Fe-4S]簇。DNA和蛋白质衍生的主要序列的NapB证实，这种蛋白质是一个dihaem的C型细胞色素，并与光谱数据一起，表明这两个NapB haems有双组氨酸连接。预测napC编码膜锚定的四血红素C型细胞色素，其显示与NirT细胞色素C家族的序列相似性。NapC可能是NapAB复合物的直接电子供体。预测napD编码可溶性胞质蛋白，napE编码单端整合膜蛋白。napDABC基因可以在大肠杆菌K-12的aeg-46.5位点识别，表明该操纵子编码周质硝酸还原酶系统，而napD和napC被鉴定为邻近真养产碱杆菌H16的napAB基因。
The napEDABC locus coding for the periplasmic nitrate reductase of Thiosphaera pantotropha has been cloned and sequenced. The large and small subunits of the enzyme are coded by napA and napB. The sequence of NapA indicates that this protein binds the GMP-conjugated form of the molybdopterin cofactor. Cysteine-181 is proposed to ligate the molybdenum atom. It is inferred that the active site of the periplasmic nitrate reductase is structurally related to those of the molybdenum-dependent formate dehydrogenases and bacterial assimilatory nitrate reductases, but is distinct from that of the membrane-bound respiratory nitrate reductases. A four-cysteine motif at the N-terminus of NapA binds a [4Fe-4S] cluster. The DNA- and protein-derived primary sequence of NapB confirm that this protein is a dihaem c-type cytochrome and, together with spectroscopic data, indicate that both NapB haems have bis-histidine ligation. napC is predicted to code for a membrane-anchored tetrahaem c-type cytochrome that shows sequence similarity to the NirT cytochrome c family. NapC may be the direct electron donor to the NapAB complex. napD is predicted to encode a soluble cytoplasmic protein and napE a monotopic integral membrane protein. napDABC genes can be discerned at the aeg-46.5 locus of Escherichia coli K-12, suggesting that this operon encodes a periplasmic nitrate reductase system, while napD and napC are identified adjacent to the napAB genes of Alcaligenes eutrophus H16.