Institute of Chemistry, Leiden University , Einsteinweg 55, 2333 CC Leiden, The Netherlands.
Biochemistry. 2013 Sep 24;52(38):6615-26. doi: 10.1021/bi400450q. Epub 2013 Sep 13.
Recent studies on the electron transfer complex formed by cytochrome f and plastocyanin from Nostoc revealed that both hydrophobic and electrostatic interactions play a role in the process of complex formation. To study the balance between these two types of interactions in the encounter and the final state, the complex between plastocyanin from Phormidium laminosum and cytochrome f from Nostoc sp. PCC 7119 was investigated using NMR spectroscopy and Monte Carlo docking. Cytochrome f has a highly negative charge. Phormidium plastocyanin is similar to that from Nostoc, but the net charge of the protein is negative rather than positive. NMR titrations of Zn-substituted Phormidium plastocyanin and Nostoc cytochrome f indicated that a complex with an affinity intermediate between those of the Nostoc and Phormidium complexes is formed. Plastocyanin was found in a head-on orientation, as determined using pseudocontact shifts, similar to that in the Phormidium complex, in which the hydrophobic patch represents the main site of interaction on plastocyanin. However, the interaction in the cross-complex is dependent on electrostatics, similar to that in the Nostoc complex. The negative charge of plastocyanin decreases, but not abolishes, the attraction to cytochrome f, resulting in the formation of a more diffuse encounter complex than in the Nostoc case, as could be determined using paramagnetic relaxation spectroscopy. This work illustrates the subtle interplay of electrostatic and hydrophobic interactions in the formation of transient protein complexes. The results are discussed in the context of a model for association on the basis of hydrophobic contacts in the encounter state.
最近对来自念珠藻的细胞色素 f 和质体蓝素形成的电子转移复合物的研究表明，疏水性相互作用和静电相互作用在复合物形成过程中都起着作用。为了研究在遭遇和最终状态这两种相互作用之间的平衡，使用 NMR 光谱和蒙特卡罗对接研究了来自平裂藻的质体蓝素和来自念珠藻 sp. PCC 7119 的细胞色素 f 之间的复合物。细胞色素 f 带高度负电荷。平裂藻质体蓝素与来自念珠藻的质体蓝素相似，但蛋白质的净电荷为负而不是正。Zn 取代的平裂藻质体蓝素和念珠藻细胞色素 f 的 NMR 滴定表明，形成了一个亲和力介于念珠藻和平裂藻复合物之间的复合物。使用赝接触位移确定质体蓝素以头对头的取向存在，类似于在平裂藻复合物中，疏水区代表质体蓝素上的主要相互作用位点。然而，交叉复合物中的相互作用取决于静电相互作用，类似于在念珠藻复合物中。质体蓝素的负电荷降低了，但没有消除对细胞色素 f 的吸引力，导致形成的遭遇复合物比在念珠藻情况下更弥散，这可以通过顺磁弛豫光谱来确定。这项工作说明了静电相互作用和疏水性相互作用在瞬态蛋白质复合物形成中的微妙相互作用。结果在基于疏水接触的遭遇状态模型的基础上进行了讨论。
