Fiedler T J, Davey C A, Fenna R E
Department of Biochemistry and Molecular Biology, University of Miami Medical School, Miami, Florida 33136, USA.
J Biol Chem. 2000 Apr 21;275(16):11964-71. doi: 10.1074/jbc.275.16.11964.
The x-ray crystal structure of human myeloperoxidase has been extended to 1.8 A resolution, using x-ray data recorded at -180 degrees C (r = 0.197, free r = 0.239). Results confirm that the heme is covalently attached to the protein via two ester linkages between the carboxyl groups of Glu(242) and Asp(94) and modified methyl groups on pyrrole rings A and C of the heme as well as a sulfonium ion linkage between the sulfur atom of Met(243) and the beta-carbon of the vinyl group on pyrrole ring A. In the native enzyme a bound chloride ion has been identified at the amino terminus of the helix containing the proximal His(336). Determination of the x-ray crystal structure of a myeloperoxidase-bromide complex (r = 0.243, free r = 0.296) has shown that this chloride ion can be replaced by bromide. Bromide is also seen to bind, at partial occupancy, in the distal heme cavity, in close proximity to the distal His(95), where it replaces the water molecule hydrogen bonded to Gln(91). The bromide-binding site in the distal cavity appears to be the halide-binding site responsible for shifts in the Soret band of the absorption spectrum of myeloperoxidase. It is proposed that halide binding to this site inhibits the enzyme by effectively competing with H(2)O(2) for access to the distal histidine, whereas in compound I, the same site may be the halide substrate-binding site.
利用在-180℃记录的X射线数据（R = 0.197，自由R = 0.239），将人髓过氧化物酶的X射线晶体结构分辨率扩展至1.8埃。结果证实，血红素通过Glu(242)和Asp(94)羧基之间的两个酯键、血红素吡咯环A和C上的修饰甲基以及Met(243)的硫原子与吡咯环A上乙烯基的β-碳之间的硫鎓离子键与蛋白质共价连接。在天然酶中，已在含有近端His(336)的螺旋的氨基末端鉴定出一个结合的氯离子。髓过氧化物酶-溴化物复合物的X射线晶体结构测定（R = 0.243，自由R = 0.296）表明，该氯离子可被溴离子取代。还观察到溴离子以部分占据的形式结合在远端血红素腔中，紧邻远端His(95)，在那里它取代了与Gln(91)氢键结合的水分子。远端腔中的溴离子结合位点似乎是负责髓过氧化物酶吸收光谱Soret带位移的卤化物结合位点。有人提出，卤化物与该位点的结合通过与H(2)O(2)有效竞争进入远端组氨酸而抑制酶，而在化合物I中，同一位点可能是卤化物底物结合位点。
