The Cys-Tyr Cross-Link of Cysteine Dioxygenase Changes the Optimal pH of the Reaction without a Structural Change

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• 作者：Casey G. Davies ; Matthias Fellner ; Egor P. Tchesnokov ; Sigurd M. Wilbanks ; Guy N. L. Jameson
• 刊名：Biochemistry
• 出版年：2014
• 出版时间：December 23, 2014
• 年：2014
• 卷：53
• 期：50
• 页码：7961-7968
• 全文大小：356K
• ISSN：1520-4995

文摘

Cysteine dioxygenase (CDO) is a non-heme monoiron enzyme with an unusual posttranslational modification in the proximity of the ferrous iron active site. This modification, a cysteine to tyrosine thioether bond, cross-links two 尾-strands of the 尾-barrel. We have investigated its role in catalysis through a combined crystallographic and kinetic approach. The C93G variant lacks the cross-link and shows little change in structure from that of the wild type, suggesting that the cross-link does not stabilize an otherwise unfavorable conformation. A pH-dependent kinetic study shows that both cross-linked and un-cross-linked CDO are active but the optimal pH decreases with the presence of the cross-link. This result reflects the effect of the thioether bond on the pK_a of Y157 and this residue鈥檚 role in catalysis. At higher pH values, k_cat is also higher for the cross-linked form, extending the pH range of activity. We therefore propose that the cross-link also increases activity by controlling deleterious interactions involving the thiol/ate of C93.