Larom Shirley, Salama Faris, Schuster Gadi, Adir Noam
Faculty of Biology and Schulich Faculty of Chemistry, Technion-Israel Institute of Technology, Haifa 32000, Israel.
Proc Natl Acad Sci U S A. 2010 May 25;107(21):9650-5. doi: 10.1073/pnas.1000187107. Epub 2010 May 10.
The initial steps of oxygenic photosynthetic electron transfer occur within photosystem II, an intricate pigment/protein transmembrane complex. Light-driven electron transfer occurs within a multistep pathway that is efficiently insulated from competing electron transfer pathways. The heart of the electron transfer system, composed of six linearly coupled redox active cofactors that enable electron transfer from water to the secondary quinone acceptor Q(B), is mainly embedded within two proteins called D1 and D2. We have identified a site in silico, poised in the vicinity of the Q(A) intermediate quinone acceptor, which could serve as a potential binding site for redox active proteins. Here we show that modification of Lysine 238 of the D1 protein to glutamic acid (Glu) in the cyanobacterium Synechocystis sp. PCC 6803, results in a strain that grows photautotrophically. The Glu thylakoid membranes are able to perform light-dependent reduction of exogenous cytochrome c with water as the electron donor. Cytochrome c photoreduction by the Glu mutant was also shown to significantly protect the D1 protein from photodamage when isolated thylakoid membranes were illuminated. We have therefore engineered a novel electron transfer pathway from water to a soluble protein electron carrier without harming the normal function of photosystem II.
光合放氧电子传递的初始步骤发生在光系统II内，这是一种复杂的色素/蛋白质跨膜复合物。光驱动的电子传递发生在一个多步骤途径中，该途径与竞争性电子传递途径有效隔离。电子传递系统的核心由六个线性耦合的氧化还原活性辅因子组成，这些辅因子能够使电子从水转移到次级醌受体Q(B)，主要嵌入在两种名为D1和D2的蛋白质中。我们在计算机上确定了一个位于Q(A)中间醌受体附近的位点，它可能作为氧化还原活性蛋白质的潜在结合位点。在这里，我们表明，在集胞藻PCC 6803中，将D1蛋白的赖氨酸238修饰为谷氨酸（Glu），会产生一种能进行光自养生长的菌株。Glu类囊体膜能够以水为电子供体进行光依赖的外源细胞色素c还原。当分离的类囊体膜被光照时，Glu突变体的细胞色素c光还原也被证明能显著保护D1蛋白免受光损伤。因此，我们设计了一条从水到可溶性蛋白质电子载体的新型电子传递途径，而不损害光系统II的正常功能。
