PhD Programme in Experimental Biology and Biomedicine, Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.
Institute for Interdisciplinary Research, University of Coimbra, Coimbra, Portugal.
J Exp Bot. 2019 Apr 12;70(7):2059-2076. doi: 10.1093/jxb/erz034.
Members of the pepsin-like family (A1) of aspartic proteases (APs) are widely distributed in plants. A large number of genes encoding putative A1 APs are found in different plant genomes, the vast majority of which exhibit distinct features when compared with the so-called typical APs (and, therefore, grouped as atypical and nucellin-like APs). These features include the absence of the plant-specific insert; an unusually high number of cysteine residues; the nature of the amino acids preceding the first catalytic aspartate; and unexpected localizations. The over-representation of atypical and nucellin-like APs in plants is suggestive of greater diversification of protein functions and a more regulatory role for these APs, as compared with the housekeeping function generally attributed to typical APs. New functions have been uncovered for non-typical APs, with proposed roles in biotic and abiotic stress responses, chloroplast metabolism, and reproductive development, clearly suggesting functional specialization and tight regulation of activity. Furthermore, unusual enzymatic properties have also been documented for some of these proteases. Here, we give an overview of the current knowledge on the distinctive features and functions of both atypical and nucellin-like APs, and discuss this emerging pattern of functional complexity and specialization among plant pepsin-like proteases.
胃蛋白酶样家族（A1）的天冬氨酸蛋白酶（APs）成员广泛分布于植物中。在不同的植物基因组中发现了大量编码假定 A1 APs 的基因，其中绝大多数与所谓的典型 APs 相比具有明显的特征（因此被归类为非典型和核蛋白样 APs）。这些特征包括缺乏植物特异性插入序列；异常高数量的半胱氨酸残基；第一个催化天冬氨酸之前氨基酸的性质；以及意想不到的定位。与通常归因于典型 APs 的管家功能相比，非典型和核蛋白样 APs 在植物中的过度表达表明蛋白质功能的更大多样化和这些 APs 的更多调节作用。非典型 APs 的新功能已经被揭示，它们在生物和非生物胁迫反应、叶绿体代谢和生殖发育中具有潜在的作用，这清楚地表明了功能的专业化和活性的紧密调节。此外，一些这些蛋白酶还具有不寻常的酶学特性。在这里，我们概述了非典型和核蛋白样 APs 的独特特征和功能的最新知识，并讨论了植物胃蛋白酶样蛋白酶之间这种新兴的功能复杂性和专业化模式。
