STRUCTURE AND ROLE OF THE CALCIUM COFACTOR IN PHOTOSYNTHETIC OXYGEN EVOLUTION

钙辅助因子在光合作用释氧中的结构和作用

• 批准号: 8169975
• 负责人: VITTAL YACHANDRA
• 金额: $ 1.36万
• 依托单位: STANFORD UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-05-01 至 2011-02-28
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8169975
• 关键词: Algae; Binding; Binding Sites; Biochemical; Calcium; Charge; Computer Retrieval of Information on Scientific Projects Database; Couples; Cyanobacterium; Dioxygen; Electrons; Evolution; Funding; Grant; Institution; Investigation; Membrane; Oxygen; Plants; Proteins; Protons; Relative (related person); Research; Research Personnel; Resources; Role; Sampling; Site; Source; Structure; Thylakoid Membranes; United States National Institutes of Health; Water; cofactor; oxidation; photosystem II; research study; vector

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Photosynthetic water oxidation takes place within Photosystem II (PS II), which is embedded in the thylakoid membranes of green plants, cyanobacteria and algae. Within PS II, the Mn cluster couples the one electron primary charge separation (photo-oxidation) with the four-electron water oxidation cycling through ?S-states? S0 through S4, storing oxidative equivalents serially until it reaches S4, whereupon it oxidizes two substrate water molecules to dioxygen, and returns to the S0 state. Calcium is an essential cofactor and without it the OEC cannot catalyze the oxidation of water into dioxygen, protons, and electrons. Calcium has been shown to be essential for the S2 to S3 state transition and subsequent oxygen evolution. Both XANES and EXAFS experiments have been carried out at the Mn K-edge of the OEC to determine the oxidation states and structural information about the Mn site. In comparison, there have been fewer spectroscopic investigation of the calcium cofactor. Most studies on Ca in PSII have been biochemical, because Ca has no easy spectroscopic handle. The structure of the Ca cofactor binding site has generated considerable discussion. To probe it, Ca in OEC might be substituted by Sr chemically or biochemically by growing cyanobacteria in Ca depleted Sr media, which binds at the Ca site within the protein. Under previous proposals our group has carried out Ca and Sr K-edge EXAFS experiments to resolve the question of proximity of the Ca/Sr to the Mn4-cluster of OEC. By using Ca EXAFS of the native PS II and Sr EXAFS on Sr-reactivated PS II membranes we have confirmed the proximity of the Ca/Sr at 3.5A to the Mn-cluster in the S1 dark stable state of the OEC. Using polarized Sr EXAFS on oriented Sr-reactivated samples the averaged Sr-Mn vector orientation relative to the membrane normal was determined to be within 0-23 degree. The present challenge is to determine the Mn4-Ca interactions.

该子项目是利用 由NIH/NCRR资助的中心赠款提供的资源。子项目和 研究者（PI）可能从另一个NIH来源获得了主要资金， 因此可以在其他CRISP条目中表示。所列机构为 研究中心，而研究中心不一定是研究者所在的机构。 光合水氧化发生在光系统II（PS II）内，其嵌入在绿色植物、蓝细菌和藻类的类囊体膜中。在PS II，锰簇耦合的一个电子初级电荷分离（光氧化）与四电子水氧化循环通过？国、州？从S 0到S4，连续地存储氧化当量，直到它到达S4，于是它将两个底物水分子氧化成分子氧，并返回到S 0状态。钙是一种重要的辅因子，没有它，OEC就不能催化水氧化成分子氧、质子和电子。钙已被证明是必不可少的S2到S3状态的转变和随后的氧的演变。XANES和EXAFS实验已经进行了锰K-边缘的OEC，以确定的氧化态和结构信息的Mn网站。相比之下，钙辅因子的光谱研究较少。由于Ca在光谱上不易处理，所以对PSII中Ca的研究大多是生物化学的。钙辅因子结合位点的结构引起了相当多的讨论。为了探测它，OEC中的Ca可能被Sr化学或生物化学取代，通过在Ca耗尽的Sr介质中生长蓝藻，其结合在蛋白质内的Ca位点。 根据以前的建议，我们的小组已经进行了Ca和Sr的K边EXAFS实验，以解决的Ca/Sr的Mn 4-集群的OEC的接近的问题。通过使用Ca EXAFS的原生PS II和Sr的EXAFS的Sr-再活化PS II膜，我们已经证实了接近的Ca/Sr在3.5A的Mn-集群在S1暗稳定状态的OEC。使用极化Sr EXAFS取向Sr-再活化样品的平均Sr-Mn矢量取向相对于膜法线被确定为在0-23度。目前的挑战是确定Mn 4-Ca相互作用。