Wallace T P, Stewart A C, Pappin D, Howe C J
Department of Biochemistry, University of Cambridge, UK.
Mol Gen Genet. 1989 Apr;216(2-3):334-9. doi: 10.1007/BF00334373.
A 9 kDa polypeptide which is loosely attached to the inner surface of the thylakoid membrane and is important for the oxygen-evolving activity of Photosystem II in the thermophilic cyanobacterium Phormidium laminosum has been purified, a partial amino acid sequence obtained and its gene cloned and sequenced. The derived amino acid sequence indicates that the 9 kDa polypeptide is initially synthesised with an N-terminal leader sequence of 44 amino acids to direct it across the thylakoid membrane. The leader sequence consists of a positively charged N-terminal region, a long hydrophobic region and a typical cleavage site. These features have analogous counterparts in the "thylakoid-transfer domain" of lumenal polypeptides from chloroplasts of higher plants. These findings support the view of the proposed function of this domain in the two-stage processing model for import of lumenal, nuclear-encoded polypeptides. In addition, there is striking primary sequence homology between the leader sequences of the 9 kDa polypeptide and those of alkaline phosphatase (from the periplasmic space of Escherichia coli) and, particularly in the region of the cleavage site, the 16 kDa polypeptide of the oxygen-evolving apparatus in the thylakoid lumen of spinach chloroplasts.
一种与嗜热蓝细菌层状席藻（Phormidium laminosum）中类囊体膜内表面松散结合且对光系统II的放氧活性很重要的9 kDa多肽已被纯化，获得了其部分氨基酸序列，并克隆和测定了其基因序列。推导的氨基酸序列表明，该9 kDa多肽最初合成时带有一个44个氨基酸的N端前导序列，以引导其穿过类囊体膜。前导序列由一个带正电荷的N端区域、一个长的疏水区域和一个典型的切割位点组成。这些特征在高等植物叶绿体腔多肽的“类囊体转移结构域”中有类似的对应物。这些发现支持了该结构域在腔中核编码多肽导入的两阶段加工模型中所提出功能的观点。此外，9 kDa多肽的前导序列与碱性磷酸酶（来自大肠杆菌周质空间）的前导序列之间存在显著的一级序列同源性，特别是在切割位点区域，与菠菜叶绿体类囊体腔中放氧装置的16 kDa多肽的前导序列同源。
