Dynamic Changes in the Proteome of Synechocystis 6803 in Response to CO2 Limitation Revealed by Quantitative Proteomics

Cyanobacteria developed efficient carbon concentrating mechanisms which significantly improve the photosynthetic performance and survival of cells under limiting CO2 conditions. Dynamic changes of the Synechocystis proteome to CO2 limitation were investigated using shotgun LC−MS/MS approach with isobaric tag for relative and absolute quantification (iTRAQ) technique. Synechocystis cells grown at high (3%) CO2 were shifted to air-level CO2 followed by protein extraction after 6, 24, and 72 h. About 19% of the cyanobacterial proteome was identified and the expression changes were quantified for 17% of theoretical ORFs. For 76 proteins, up- or down-regulation was found to be significant (more than 1.5 or less than 0.7). Major changes were observed in proteins participating in inorganic carbon uptake, CO2 fixation, nitrogen transport and assimilation, as well as in the protection of the photosynthetic machinery from excess of light. Further, a number of hypothetical proteins with unknown functions were discovered. In general, the cells appear to acclimate to low CO2 without a significant stress since the stress-related molecular chaperones were down-regulated and only a minor decline was detected for proteins of phycobilisomes, photosynthetic complexes, and translation machinery. The results of iTRAQ experiment were validated by the Western blot analysis for selected proteins.

蓝藻进化出高效的碳浓缩机制，显著提升了细胞在二氧化碳限制条件下的光合作用性能和存活率。通过使用等量标记相对和绝对定量（iTRAQ）技术的液相色谱-串联质谱（LC-MS/MS）方法，对蓝藻（Synechocystis）蛋白组在二氧化碳限制条件下的动态变化进行了研究。将Synechocystis细胞在高浓度（3%）二氧化碳条件下培养后，将其转移到大气水平二氧化碳中，并在6小时、24小时和72小时后提取蛋白质。鉴定出约19%的蓝藻蛋白组，并对17%的理论开放阅读框（ORF）的表达变化进行了量化。在76个蛋白质中，发现上调或下调表达具有显著性（上调超过1.5倍或下调低于0.7倍）。主要变化发生在参与无机碳摄取、二氧化碳固定、氮的运输和同化以及保护光合作用机制免受光照过量损伤的蛋白质中。此外，还发现了一些功能未知的假设性蛋白质。总体而言，细胞似乎能够适应低二氧化碳环境而不会产生显著的压力，因为与压力相关的分子伴侣下调，且仅检测到微小的下降，涉及蓝藻素、光合作用复合物和翻译机制的蛋白质。通过针对选定蛋白质的Western blot分析验证了iTRAQ实验的结果。