Department of Biochemistry, University of Otago, P.O. Box 56, Dunedin, 9054, New Zealand.
Eur Biophys J. 2013 Dec;42(11-12):787-93. doi: 10.1007/s00249-013-0926-9. Epub 2013 Sep 13.
Psb27 associates with the CP43 subunit of photosystem II during biogenesis of the photosystem. Several models have been proposed for the interaction between Psb27 and CP43. The utility of predictions and hypotheses arising from these models depends on the accuracy of the Psb27 structure used in the model. Two of the Psb27 structures used to model the Psb27-CP43 interaction place residue E98 on the surface of Psb27 and D14 in a position to form hydrogen bonds that stabilise the fold of the protein; however, a third structure questions the surface exposure of E98 and does not identify significant interactions of D14. Here we present evidence that D14 contributes to the thermal stability of Psb27 and that E98 is located on the surface. A D14A mutation was shown to reduce the apparent midpoint of unfolding of Psb27 by 16 °C. Four highly conserved surface residues and E98 were subject to charge-reversal mutations (R54E, R94E, E98R, E103R, R108E). The stabilities of the charge-reversal variants and the unmodified control were similar, suggesting E98 is a surface residue. Placing E98 in the correct, surface position will support more reliable models of the interaction of Psb27 with CP43.
Psb27 在光合作用系统的生物发生过程中与光系统 II 的 CP43 亚基结合。已经提出了几种 Psb27 和 CP43 之间相互作用的模型。这些模型产生的预测和假设的有效性取决于模型中使用的 Psb27 结构的准确性。用于模拟 Psb27-CP43 相互作用的两种 Psb27 结构将残基 E98 置于 Psb27 的表面，并将残基 D14 置于形成氢键以稳定蛋白质折叠的位置；然而，第三种结构质疑 E98 的表面暴露情况，并且没有确定 D14 的重要相互作用。在这里，我们提供了证据表明 D14 有助于 Psb27 的热稳定性，并且 E98 位于表面。D14A 突变使 Psb27 的明显展开中点降低了 16°C。四个高度保守的表面残基和 E98 发生了电荷反转突变（R54E、R94E、E98R、E103R、R108E）。电荷反转变体和未修饰对照的稳定性相似，表明 E98 是一个表面残基。将 E98 置于正确的表面位置将支持更可靠的 Psb27 与 CP43 相互作用模型。
