Stiller Olivia R, Streit Bennett R, Honzay Garrett, DuBois Jennifer L, Rodgers Kenton R, Lukat-Rodgers Gudrun S
Department of Chemistry and Biochemistry, North Dakota State University, Fargo, ND 58108-6050, USA.
Department of Chemistry and Biochemistry, Montana State University, Bozeman, MT 59717-3400, USA; Cytiva, 20 Walkup Drive, Westbourgh, MA 01581, USA.
J Inorg Biochem. 2025 Aug;269:112896. doi: 10.1016/j.jinorgbio.2025.112896. Epub 2025 Mar 15.
Coproheme decarboxylase (ChdC) catalyzes the sequential oxidative decarboxylation of coproheme III propionate side chains at positions 2 and 4 to form heme b by activation of two molecules of HO at its substrate's iron center. The coproheme III binding pocket lacks the distal His-Arg pair that polarizes and acts as a catalytic base toward activation of coordinated HO in canonical heme-dependent peroxidases. Instead ChdC from Staphylococcus aureus has a Gln (Q185). This report presents thermodynamic, kinetic, and spectroscopic results that provide comparative insight into how wild type (WT) and Q185A and Q185R variant ChdCs activate HO. Reactivities with HO and cyanide affinities at pH 7.5 follow the trend: WT > Q185R > Q185A. Both variants exhibited greater catalase efficiency than WT ChdC. Vibrational resonance Raman signatures of ferric coproheme-CN and ferrous coproheme-CO complexes of WT, Q185A, and Q185R SaChdCs revealed that the Arg mutation does not significantly alter the distal environment while Q185A has a more open active site. Together these data are consistent with a modest role for Q185 in promoting the decarboxylation reaction. A model for the proton transfer required for HO activation that involves the Gln185 iminol tautomer is presented. The three ChdCs reacted with chlorite to generate harderoheme III and heme b to varying extents. In reaction with chlorite, coproheme III:SaChdC was cleanly converted to harderoheme III:SaChdC, which exhibited vinyl bending and stretching modes at 423 and 1622 cm, respectively. Differences in SaChdC reactivity with ClO and HO relative to those of chlorite dismutase and peroxidases, respectively, are discussed.
粪卟啉原脱羧酶（ChdC）通过在其底物的铁中心激活两分子的HO，催化粪卟啉原III丙酸侧链在2位和4位的顺序氧化脱羧反应，形成血红素b。粪卟啉原III结合口袋缺乏在典型的血红素依赖性过氧化物酶中使配位的HO极化并作为催化碱起作用的远端His-Arg对。相反，金黄色葡萄球菌的ChdC有一个Gln（Q185）。本报告展示了热力学、动力学和光谱学结果，这些结果为深入比较野生型（WT）以及Q185A和Q185R变体ChdC如何激活HO提供了见解。在pH 7.5时与HO的反应性和与氰化物的亲和力遵循以下趋势：WT > Q185R > Q185A。两种变体均表现出比野生型ChdC更高的过氧化氢酶效率。WT、Q185A和Q185R金黄色葡萄球菌ChdC的高铁粪卟啉 - CN和亚铁粪卟啉 - CO复合物的振动共振拉曼特征表明，Arg突变不会显著改变远端环境，而Q185A具有更开放的活性位点。这些数据共同表明Q185在促进脱羧反应中起适度作用。提出了一个涉及Gln185亚胺醇互变异构体的HO激活所需质子转移模型。三种ChdC与亚氯酸盐反应，不同程度地生成硬卟啉原III和血红素b。在与亚氯酸盐的反应中，粪卟啉原III:金黄色葡萄球菌ChdC被干净地转化为硬卟啉原III:金黄色葡萄球菌ChdC，其分别在423和1622 cm处表现出乙烯基弯曲和拉伸模式。讨论了金黄色葡萄球菌ChdC与ClO和HO的反应性相对于亚氯酸盐歧化酶和过氧化物酶的反应性的差异。
