Komenda Josef, Knoppová Jana, Krynická Vendula, Nixon Peter J, Tichý Martin
Institute of Microbiology, Academy of Sciences, Opatovický mlýn, Trebon, Czech Republic.
Biochim Biophys Acta. 2010 May;1797(5):566-75. doi: 10.1016/j.bbabio.2010.02.006. Epub 2010 Feb 11.
The FtsH2 protease, encoded by the slr0228 gene, plays a key role in the selective degradation of photodamaged D1 protein during the repair of Photosystem II (PSII) in the cyanobacterium Synechocystis sp. PCC 6803. To test whether additional proteases might be involved in D1 degradation during high rates of photodamage, we have studied the synthesis and degradation of the D1 protein in DeltaPsbO and DeltaPsbV mutants, in which the CaMn(4) cluster catalyzing oxygen evolution is less stable, and in the D1 processing mutants, D1-S345P and DeltaCtpA, which are unable to assemble a functional cluster. All four mutants exhibited a dramatically increased rate of D1 degradation in high light compared to the wild-type. Additional inactivation of the ftsH2 gene slowed the rate of D1 degradation dramatically and increased the level of PSII complexes. We conclude that FtsH2 plays a major role in the degradation of both precursor and mature forms of D1 following donor-side photoinhibition. However, this conclusion concerned only D1 assembled into larger complexes containing at least D2 and CP47. In the DeltapsbEFLJ deletion mutant blocked at an early stage in PSII assembly, unassembled D1 protein was efficiently degraded in the absence of FtsH2 pointing to the involvement of other protease(s). Significantly, the DeltaPsbO mutant displayed unusually low levels of cellular chlorophyll at extremely low-light intensities. The possibilities that PSII repair may limit the availability of chlorophyll for the biogenesis of other chlorophyll-binding proteins and that PsbO might have a regulatory role in PSII repair are discussed.
由slr0228基因编码的FtsH2蛋白酶，在集胞藻PCC 6803光合系统II（PSII）修复过程中光损伤D1蛋白的选择性降解中起关键作用。为了测试在高光损伤率期间是否有其他蛋白酶参与D1降解，我们研究了DeltaPsbO和DeltaPsbV突变体中D1蛋白的合成和降解情况，在这些突变体中催化放氧的CaMn(4)簇不太稳定，以及在D1加工突变体D1-S345P和DeltaCtpA中，它们无法组装功能性簇。与野生型相比，所有这四个突变体在高光下D1降解速率都显著增加。ftsH2基因的进一步失活显著减缓了D1降解速率并增加了PSII复合物的水平。我们得出结论，FtsH2在供体侧光抑制后D1前体和成熟形式的降解中起主要作用。然而，这一结论仅涉及组装到至少包含D2和CP47的较大复合物中的D1。在PSII组装早期受阻的DeltapsbEFLJ缺失突变体中，未组装的D1蛋白在没有FtsH2的情况下被有效降解，这表明有其他蛋白酶参与。值得注意的是，DeltaPsbO突变体在极低光强度下细胞叶绿素水平异常低。讨论了PSII修复可能限制叶绿素用于其他叶绿素结合蛋白生物合成的可用性以及PsbO可能在PSII修复中具有调节作用的可能性。
