Pearson D C, Gross E L, David E S
Department of Biochemistry, Ohio State University, Columbus 43210, USA.
Biophys J. 1996 Jul;71(1):64-76. doi: 10.1016/S0006-3495(96)79236-6.
The electrostatic properties of cytochrome f (cyt f), a member of the cytochrome b6f complex and reaction partner with plastocyanin (PC) in photosynthetic electron transport, are qualitatively studied with the goal of determining the mechanism of electron transfer between cyt f and PC. A crystal structure for cyt f was analyzed with the software package GRASP, revealing a large region of positive potential generated by a patch of positively charged residues (including K58, K65, K66, K122, K185, K187, and R209) and reinforced by the iron center of the heme. This positive field attracts the negative charges of the two acidic patches on the mobile electron carrier PC. Three docked complexes are obtained for the two proteins, based on electrostatic or hydrophobic interactions or both and on steric fits by manual docking methods. The first of these three complexes shows strong electrostatic interactions between K187 on cyt f and D44 on PC and between E59 on PC and K58 on cyt f. Two other manually docked complexes are proposed, implicating H87 on PC as the electron-accepting site from the iron center of cyt f through Y1. The second complex maintains the D44/K187 cross-link (but not the E59/K58 link) while increasing hydrophobic interactions between PC and cyt f. Hydrophobic interactions are increased still further in the third complex, whereas the link between K187 on cyt f and D44 on PC is broken. The proposed reaction mechanism, therefore, involves an initial electrostatic docking complex that gives rise to a nonpolar attraction between the regions surrounding H87 on PC and Y1 on cyt f, providing for an electron-transfer active complex.
细胞色素f（cyt f）是细胞色素b6f复合物的成员，在光合电子传递中与质体蓝素（PC）发生反应，本文对其静电特性进行了定性研究，目的是确定cyt f与PC之间的电子转移机制。利用GRASP软件包分析了cyt f的晶体结构，发现由一片带正电荷的残基（包括K58、K65、K66、K122、K185、K187和R209）产生的一大片正电位区域，并由血红素的铁中心增强。这个正电场吸引了移动电子载体PC上两个酸性区域的负电荷。基于静电或疏水相互作用或两者兼而有之，并通过手动对接方法进行空间拟合，得到了两种蛋白质的三种对接复合物。这三种复合物中的第一种显示出cyt f上的K187与PC上的D44之间以及PC上的E59与cyt f上的K58之间存在强静电相互作用。还提出了另外两种手动对接的复合物，表明PC上的H87是通过Y1从cyt f的铁中心接受电子的位点。第二种复合物保持了D44/K187交联（但不是E59/K58交联），同时增加了PC与cyt f之间的疏水相互作用。在第三种复合物中，疏水相互作用进一步增加，而cyt f上的K187与PC上的D44之间的连接被破坏。因此，所提出的反应机制涉及一个初始的静电对接复合物，该复合物导致PC上H87周围区域与cyt f上Y1周围区域之间产生非极性吸引力，从而形成一个电子转移活性复合物。
