Tucker D L, Hirsh K, Li H, Boardman B, Sherman L A
Department of Biological Sciences, 1392 Lilly Hall of Life Sciences, Purdue University, 47907, West Lafayette, IN, USA.
Biochim Biophys Acta. 2001 Apr 2;1504(2-3):409-22. doi: 10.1016/s0005-2728(00)00271-1.
The unicellular diazotrophic cyanobacterium, Cyanothece sp. ATCC 51142 temporally separates N2 fixation from photosynthesis. To better understand the processes by which photosynthesis is regulated, we have analyzed Photosystem (PS) II O2 evolution and the PSII lumenal proteins, especially the Mn stabilizing protein (MSP). We describe a procedure using glycine betaine to isolate photosynthetic membranes from Cyanothece sp. that have high rates of PSI and PSII activity. Analysis with these membranes demonstrated similar patterns of O2 evolution in vivo and in vitro, with a trough at the time of maximal N2 fixation and with a peak in the late light period. The pattern of PSI activity was also similar in vivo and in vitro. We cloned the genes for MSP (psbO) and the 12 kDa protein (psbU) and analyzed their transcriptional properties throughout the diurnal cycle. We suggest that the changes in PSII activity in Cyanothece sp. were due to conformational changes in a highly flexible MSP, a suggestion which can now be studied in a chimera. The Cyanothece sp. psbO gene has been transformed into Synechocystis sp. PCC 6803; MSP and O2 evolution in the resulting transformant had properties that were similar to those in Cyanothece sp., providing additional confirmation for the properties of Cyanothece sp. MSP.
单细胞固氮蓝藻Cyanothece sp. ATCC 51142在时间上分离了固氮作用与光合作用。为了更好地理解光合作用的调控过程，我们分析了光系统（PS）II的氧气释放以及PSII腔蛋白，特别是锰稳定蛋白（MSP）。我们描述了一种使用甘氨酸甜菜碱从Cyanothece sp.中分离光合膜的方法，这些光合膜具有较高的PSI和PSII活性。对这些膜的分析表明，体内和体外的氧气释放模式相似，在最大固氮时出现低谷，在光照后期出现峰值。PSI活性模式在体内和体外也相似。我们克隆了MSP（psbO）和12 kDa蛋白（psbU）的基因，并分析了它们在整个昼夜周期中的转录特性。我们认为Cyanothece sp.中PSII活性的变化是由于高度灵活的MSP的构象变化引起的，这一观点现在可以在嵌合体中进行研究。Cyanothece sp.的psbO基因已被转化到集胞藻属PCC 6803中；所得转化体中的MSP和氧气释放具有与Cyanothece sp.中相似的特性，为Cyanothece sp. MSP的特性提供了额外的证实。
