Bamford Vicki A, Bruno Stefano, Rasmussen Tim, Appia-Ayme Corinne, Cheesman Myles R, Berks Ben C, Hemmings Andrew M
Centre for Metalloprotein Spectroscopy and Biology, School of Biological Sciences and School of Chemical Sciences, University of East Anglia, Norwich NR4 7TJ, UK.
EMBO J. 2002 Nov 1;21(21):5599-610. doi: 10.1093/emboj/cdf566.
Reduced inorganic sulfur compounds are utilized by many bacteria as electron donors to photosynthetic or respiratory electron transport chains. This metabolism is a key component of the biogeochemical sulfur cycle. The SoxAX protein is a heterodimeric c-type cytochrome involved in thiosulfate oxidation. The crystal structures of SoxAX from the photosynthetic bacterium Rhodovulum sulfidophilum have been solved at 1.75 A resolution in the oxidized state and at 1.5 A resolution in the dithionite-reduced state, providing the first structural insights into the enzymatic oxidation of thiosulfate. The SoxAX active site contains a haem with unprecedented cysteine persulfide (cysteine sulfane) coordination. This unusual post-translational modification is also seen in sulfurtransferases such as rhodanese. Intriguingly, this enzyme shares further active site characteristics with SoxAX such as an adjacent conserved arginine residue and a strongly positive electrostatic potential. These similarities have allowed us to suggest a catalytic mechanism for enzymatic thiosulfate oxidation. The atomic coordinates and experimental structure factors have been deposited in the PDB with the accession codes 1H31, 1H32 and 1H33.
许多细菌利用还原态无机硫化合物作为光合或呼吸电子传递链的电子供体。这种代谢是生物地球化学硫循环的关键组成部分。SoxAX蛋白是一种参与硫代硫酸盐氧化的异二聚体c型细胞色素。已解析出嗜硫红假单胞菌光合细菌中SoxAX在氧化态下1.75 Å分辨率和连二亚硫酸盐还原态下1.5 Å分辨率的晶体结构，首次为硫代硫酸盐的酶促氧化提供了结构见解。SoxAX活性位点包含一个血红素，其具有前所未有的半胱氨酸过硫化物（半胱氨酸硫烷）配位。这种不寻常的翻译后修饰在硫转移酶如硫氰酸酶中也可见。有趣的是，这种酶与SoxAX具有进一步的活性位点特征，如相邻的保守精氨酸残基和强正静电势。这些相似性使我们能够提出酶促硫代硫酸盐氧化的催化机制。原子坐标和实验结构因子已存入蛋白质数据库，登录号为1H31、1H32和1H33。
