Yu J, Vermaas W F
Department of Botany, Arizona State University, Tempe 85287-1601.
J Biol Chem. 1993 Apr 5;268(10):7407-13.
Several mutations in psbD (coding for the photosystem II reaction protein D2) lead to a loss of the entire photosystem II complex from the thylakoid membrane. For two site-directed D2 mutants, E69V (Glu-69 mutated to Val) and ET-9 (introducing a premature stop codon in psbD), and two psbD deletion mutants, the synthesis and degradation of photosystem II reaction center components were analyzed. In E69V, no D2 or psbC-encoded CP43 was detected upon 5-min pulse labeling or Western blotting, whereas a psbDI/C transcript was present. Either D2 and CP43 are very unstable in this mutant, or the mutation causes an inhibition of translation of the psbDC operon. In E69V, the predominant lifetime of D1 is several minutes, but a small fraction of D1 remains stable in the thylakoid for several hours. In E69V, also a 43-kDa band is detected by D1 antisera. We attribute this band to a D1 cross-linking product possibly involved in D1 degradation. We identified a D1 precursor in E69V and psbDI/C/DII-, two mutants with particularly short D1 lifetimes. A unique feature of the E69V mutant is that destabilization of the photosystem II complex is triggered by a single-site mutation leading to extremely rapid turnover or lack of synthesis of D2.
psbD（编码光系统II反应蛋白D2）中的几个突变导致整个光系统II复合物从类囊体膜上丢失。对于两个定点诱变的D2突变体E69V（Glu-69突变为Val）和ET-9（在psbD中引入提前终止密码子）以及两个psbD缺失突变体，分析了光系统II反应中心组分的合成和降解。在E69V中，5分钟脉冲标记或蛋白质免疫印迹均未检测到D2或psbC编码的CP43，但存在psbDI/C转录本。要么D2和CP43在该突变体中非常不稳定，要么该突变导致psbDC操纵子的翻译受到抑制。在E69V中，D1的主要寿命为几分钟，但一小部分D1在类囊体中保持稳定数小时。在E69V中，D1抗血清也检测到一条43 kDa的条带。我们将这条带归因于可能参与D1降解的D1交联产物。我们在E69V和psbDI/C/DII-（两个D1寿命特别短的突变体）中鉴定出一种D1前体。E69V突变体的一个独特特征是，光系统II复合物的不稳定是由单点突变引发的，导致D2的周转极快或缺乏合成。
