Heme Attachment Motif Mobility Tunes Cytochrome c Redox Potential

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• 作者：Lea V. Michel ; Tao Ye ; Sarah E. J. Bowman ; Benjamin D. Levin ; Megan A. Hahn ; Brandy S. Russell ; Sean J. Elliott ; Kara L. Bren
• 刊名：Biochemistry
• 出版年：2007
• 出版时间：October 23, 2007
• 年：2007
• 卷：46
• 期：42
• 页码：11753 - 11760
• 全文大小：150K
• 年卷期：v.46,no.42(October 23, 2007)
• ISSN：1520-4995

文摘

Hydrogen exchange (HX) rates and midpoint potentials (E_m) of variants of cytochrome c fromPseudomonas aeruginosa (Pa cyt c₅₅₁) and Hydrogenobacter thermophilus (Ht cyt c₅₅₂) have beencharacterized in an effort to develop an understanding of the impact of properties of the Cys-X-X-Cys-His pentapeptide c-heme attachment (CXXCH) motif on heme redox potential. Despite structuralconservation of the CXXCH motif, Ht cyt c₅₅₂ exhibits a low level of protection from HX for amideprotons within this motif relative to Pa cyt c₅₅₁. Site-directed mutants have been prepared to determinethe structural basis for and functional implications of these variations on HX behavior. The double mutantHt-M13V/K22M displays suppressed HX within the CXXCH motif as well as a decreased E_m (by 81mV), whereas the corresponding double mutant of Pa cyt c₅₅₁ (V13M/M22K) exhibits enhanced HXwithin the CXXCH pentapeptide and a modest increase in E_m (by 30 mV). The changes in E_m correlatewith changes in axial His chemical shifts in the ferric proteins reflecting the extent of histidinate character.Thus, the mobility of the CXXCH pentapeptide is found to impact the His-Fe(III) interaction and thereforethe heme redox potential.