Evolutionary and structure-function analysis elucidates diversification of prokaryotic and eukaryotic trehalases

Trehalase catalyses the breakdown of trehalose into two glucose moieties and is ubiquitous in all organisms. Here, we provide insights into the enigmatic origin and evolution of trehalase in major species. Study of taxonomic distribution, orthology, phylogeny and functional domains indicated that trehalase possibly originates from bacteria and was transmitted to other taxa through horizontal gene transfer. Domain analysis showed that glycosyl hydrolase family 37 is present in most of the sequences and represents dominant activity during evolution, and also, illustrating that cytosolic trehalase is primitive than its transmembrane form. Furthermore, it was observed that trehalase went through domain rearrangement to facilitate its activity in adverse environmental conditions like acidic pH. Gene context analysis depicts that trehalase neighbourhood consists of sugar transport and lipid metabolism genes. This highlights their relatedness in metabolic activity and similarity in gene regulation, respectively. Evolutionary and selection pressure analysis demonstrated that trehalase genes were duplicated and evolved under purifying selection, following horizontal gene transfer. Moreover, site-specific rate of evolution emphasized conservation of functionally important residues. In comparison with acid trehalase, neutral trehalase has an extra N-terminal extension. This study serves as an instigation to understand evolution and functionality of trehalase across diverse species. Communicated by Ramaswamy H. Sarma海藻糖酶（trehalase）可催化海藻糖分解为两个葡萄糖基团，广泛分布于所有生物类群中。本研究旨在解析海藻糖酶在主要物种中神秘的起源与演化历程。对分类学分布、直系同源（orthology）、系统发育（phylogeny）及功能结构域的研究显示，海藻糖酶可能起源于细菌，并通过水平基因转移（horizontal gene transfer）传播至其他类群。结构域分析表明，糖基水解酶家族37（glycosyl hydrolase family 37）存在于绝大多数序列中，是演化过程中占据主导的活性形式；同时研究证实，胞质海藻糖酶相较于其跨膜形式更为原始。此外，研究发现海藻糖酶发生了结构域重排，以在酸性pH等极端环境中维持催化活性。基因邻区分析显示，海藻糖酶的侧翼基因包含糖转运与脂质代谢相关基因，这分别揭示了二者在代谢活性上的相关性以及基因调控上的相似性。演化与选择压力分析结果表明，海藻糖酶基因在经历水平基因转移后发生了复制，并在纯化选择（purifying selection）作用下持续演化。此外，位点特异性进化速率分析进一步证实了功能关键氨基酸残基的保守性。相较于酸性海藻糖酶，中性海藻糖酶带有一段额外的N端延伸序列。本研究为解析不同物种中海藻糖酶的演化与功能提供了重要的研究基础。本稿件由Ramaswamy H. Sarma转交。