Department of Chemistry and Biochemistry, 106 Hughes Laboratories, Miami University, Oxford, OH 45056, USA.
Biomolecules. 2021 Apr 26;11(5):638. doi: 10.3390/biom11050638.
The pentapeptide repeat protein (PRP) superfamily, identified in 1998, has grown to nearly 39,000 sequences from over 3300 species. PRPs, recognized as having at least eight contiguous pentapeptide repeats (PRs) of a consensus pentapeptide sequence, adopt a remarkable structure, namely, a right-handed quadrilateral β-helix with four consecutive PRs forming a single β-helix coil. Adjacent coils join together to form a β-helix "tower" stabilized by β-ladders on the tower faces and type I, type II, or type IV β-turns facilitating an approximately -90° redirection of the polypeptide chain joining one coil face to the next. PRPs have been found in all branches of life, but they are predominantly found in cyanobacteria. Cyanobacteria have existed on earth for more than two billion years and are thought to be responsible for oxygenation of the earth's atmosphere. Filamentous cyanobacteria such as sp. strain PCC 7120 may also represent the oldest and simplest multicellular organisms known to undergo cell differentiation on earth. Knowledge of the biochemical function of these PRPs is essential to understanding how ancient cyanobacteria achieved functions critical to early development of life on earth. PRPs are predicted to exist in all cyanobacteria compartments including thylakoid and cell-wall membranes, cytoplasm, and thylakoid periplasmic space. Despite their intriguing structure and importance to understanding ancient cyanobacteria, the biochemical functions of PRPs in cyanobacteria remain almost completely unknown. The precise biochemical function of only a handful of PRPs is currently known from any organisms, and three-dimensional structures of only sixteen PRPs or PRP-containing multidomain proteins from any organism have been reported. In this review, the current knowledge of the structures and functions of PRPs is presented and discussed.
五肽重复蛋白（PRP）超家族于 1998 年被发现，其序列已从 3300 多种物种中增长到近 39000 个。PRP 被认为至少有八个连续的五肽重复（PR），这些 PR 具有一个共识的五肽序列，采用一种显著的结构，即右手四边形β-螺旋，其中四个连续的 PR 形成单个β-螺旋线圈。相邻的线圈连接在一起，形成一个β-螺旋“塔”，由塔面上的β-梯稳定，I 型、II 型或 IV 型β-转角有助于多肽链大约 -90°的方向改变，将一个线圈面连接到下一个线圈面。PRP 存在于生命的所有分支中，但主要存在于蓝细菌中。蓝细菌在地球上已经存在了超过 20 亿年，被认为是地球大气氧化的原因。丝状蓝细菌，如 sp. 菌株 PCC 7120，也可能代表地球上已知的最古老和最简单的多细胞生物，它们在地球上经历细胞分化。了解这些 PRP 的生化功能对于理解古老的蓝细菌如何获得对地球生命早期发展至关重要的功能至关重要。PRP 预计存在于所有蓝细菌隔室中，包括类囊体和细胞壁膜、细胞质和类囊体周质空间。尽管它们的结构引人入胜，对理解古老的蓝细菌很重要，但蓝细菌中 PRP 的生化功能几乎完全未知。目前仅从少数几种生物体中了解到 PRP 的精确生化功能，并且仅从任何生物体报告了十六个 PRP 或含有 PRP 的多域蛋白的三维结构。在这篇综述中，介绍和讨论了 PRP 的结构和功能的当前知识。
