Vacuolar processing enzyme (VPE) is a cysteine-type endopeptidase that has a substrate-specificity for asparagine or aspartic acid residues and cleaves peptide bonds at their carboxyl-terminal side. Various vacuolar proteins are synthesized as larger proprotein precursors, and VPE is an important initiator of maturation and activation of these proteins. It mediates programmed cell death (PCD) by provoking vacuolar rupture and initiating the proteolytic cascade leading to PCD. Vacuolar processing enzyme also possesses a peptide ligation activity, which is responsible for producing cyclic peptides in several plant species. These unique functions of VPE support developmental and environmental responses in plants. The number of VPE homologues is higher in angiosperm species, indicating that there has been differentiation and specialization of VPE function over the course of evolution. Angiosperm VPEs are separated into two major types: the γ-type VPEs, which are expressed mainly in vegetative organs, and the β-type VPEs, whose expression occurs mainly in storage organs; in eudicots, the δ-type VPEs are further separated within γ-type VPEs. This review also considers the importance of processing and peptide ligation by VPE in vacuolar protein maturation.

中文翻译：

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叶片中的酶处理植物的生命周期。

液泡加工酶（VPE）是一种半胱氨酸型内肽酶，对天冬酰胺或天冬氨酸残基具有底物特异性，并在其羧基末端切割肽键。各种液泡蛋白被合成为较大的前蛋白前体，VPE是这些蛋白成熟和激活的重要引发剂。它通过引起液泡破裂并引发导致PCD的蛋白水解级联来介导程序性细胞死亡（PCD）。液泡加工酶还具有肽连接活性，其负责在几种植物物种中产生环状肽。VPE的这些独特功能可支持植物的发育和环境响应。在被子植物中，VPE同源物的数量更高，表明在进化过程中VPE功能已经分化和专业化。被子植物VPE分为两种主要类型：主要在营养器官中表达的γ型VPE和主要在贮藏器官中表达的β型VPE。在双子叶植物中，δ型VPE在γ型VPE中进一步分离。这篇综述还考虑了VPE在液泡蛋白成熟中进行加工和肽连接的重要性。