Structures of Cytochrome c-549 and Cytochrome c6 from the Cyanobacterium Arthrospira maxima

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• 作者：Michael R. Sawaya ; David W. Krogmann ; Ahmed Serag ; Kwok Ki Ho ; Todd O. Yeates ; and Cheryl A. Kerfeld
• 刊名：Biochemistry
• 出版年：2001
• 出版时间：August 7, 2001
• 年：2001
• 卷：40
• 期：31
• 页码：9215 - 9225
• 全文大小：822K
• 年卷期：v.40,no.31(August 7, 2001)
• ISSN：1520-4995

文摘

Cytochrome c₆ and cytochrome c-549 are small (89 and 130 amino acids, respectively)monoheme cytochromes that function in photosynthesis. They appear to have descended relatively recentlyfrom the same ancestral gene but have diverged to carry out very different functional roles, underscoredby the large difference between their midpoint potentials of nearly 600 mV. We have determined theX-ray crystal structures of both proteins isolated from the cyanobacterium Arthrospira maxima. The twostructures are remarkably similar, superimposing on backbone atoms with an rmsd of 0.7 Å. Comparisonof the two structures suggests that differences in solvent exposure of the heme and the electrostaticenvironment of the heme propionates, as well as in heme iron ligation, are the main determinants ofmidpoint potential in the two proteins. In addition, the crystal packing of both A. maxima cytochromec-549 and cytochrome c₆ suggests that the proteins oligomerize. Finally, the cytochrome c-549 dimer weobserve can be readily fit into the recently described model of cyanobacterial photosystem II.