C-terminal processing of reaction center protein D1 is essential for the function and assembly of photosystem II in Arabidopsis
C-terminal processing of reaction center protein D1 is essential for the function and assembly of photosystem II in Arabidopsis
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DOI：
10.1073/pnas.1313894110
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发表时间：
2013-10-01
影响因子：
11.1
通讯作者：
Luan, Sheng
中科院分区：
文献类型：
--
作者：
Che, Yufen;Fu, Aigen;Luan, Sheng
光系统II(PSII)反应中心蛋白D1被合成为具有短C端延伸的前体(PD1)。PD1被羧基末端多肽酶A加工成成熟的D1，以去除C-末端延伸，形成活性蛋白。在这里，我们报道了拟南芥编码D1C末端处理酶(AtCtpA)基因在叶绿体类囊体腔中的功能特征。重组AtCtpA将PD1转化为成熟的D1，而缺失AtCtpA的突变体保留了所有的D1的前体形式，证实了AtCtpA单独负责加工。与蓝藻CTPA一样，敲除的拟南芥atctpa突变体在正常生长条件下是致命的，但在弱光条件下可以在蔗糖的作用下存活。然而，存活的植物在PSII和类囊体堆积方面表现出不足。令人惊讶的是，与蓝藻突变体不同的是，拟南芥突变体保留了PSII复合体的单体和二聚体形式，尽管没有功能，但包含核心亚基和外在亚基。该突变体也基本上不存在PSII超复合体，这在D1成熟和超复合体组装之间提供了一种意想不到的联系。一个表达约2%野生型AtCtpA的敲除突变体在弱光下生长正常，但在强光下发育迟缓并积累了PD1，表明C-末端加工延迟。虽然我们的研究证明了C-末端D1处理在PSII生物发生中的功能意义，但我们的研究揭示了D1成熟与PSII超复合体组装之间的意外联系，为探索捕光复合体与PSII核心复合体的结合机制开辟了一条途径。
Photosystem II (PSII) reaction center protein D1 is synthesized as a precursor (pD1) with a short C-terminal extension. The pD1 is processed to mature D1 by carboxyl-terminal peptidase A to remove the C-terminal extension and form active protein. Here we report functional characterization of the Arabidopsis gene encoding D1 C-terminal processing enzyme (AtCtpA) in the chloroplast thylakoid lumen. Recombinant AtCtpA converted pD1 to mature D1 and a mutant lacking AtCtpA retained all D1 in precursor form, confirming that AtCtpA is solely responsible for processing. As with cyanobacterial ctpa, a knockout Arabidopsis atctpa mutant was lethal under normal growth conditions but was viable with sucrose under low-light conditions. Viable plants, however, showed deficiencies in PSII and thylakoid stacking. Surprisingly, unlike its cyanobacterial counterpart, the Arabidopsis mutant retained both monomer and dimer forms of the PSII complexes that, although nonfunctional, contained both the core and extrinsic subunits. This mutant was also essentially devoid of PSII supercomplexes, providing an unexpected link between D1 maturation and supercomplex assembly. A knock-down mutant expressing about 2% wild-type level of AtCtpA showed normal growth under low light but was stunted and accumulated pD1 under high light, indicative of delayed C-terminal processing. Although demonstrating the functional significance of C-terminal D1 processing in PSII biogenesis, our study reveals an unsuspected link between D1 maturation and PSII supercomplex assembly in land plants, opening an avenue for exploring the mechanism for the association of light-harvesting complexes with the PSII core complexes.