ABSTRACT

Serine proteases are a class of versatile proteolytic enzymes. They are necessary for protein catabolism, intracellular amino acid turnover, and regulation of proteins involved in diverse molecular and cellular processes across taxa. In this study, bioinformatic analyses revealed a significantly large number of serine proteases in the halotolerant cyanobacterium Halothece sp. PCC7418 (hereafter referred to as Halothece 7418) compared to the model freshwater cyanobacterium Synechococcus elongatus PCC7942 (hereafter referred to as S. elongatus 7942). The cyanobacterial serine proteases are likely derived from different linages since no conserved motifs were detected. The presence of highly diverse serine proteases in Halothece 7418 implicated an evolutionary-mediated modification of several proteases, which may play numerous physiological roles. We also examined the gene expression patterns of 34 serine protease encoding genes in Halothece 7418 exposed to salt stress. Our results revealed that several serine protease genes were drastically up–regulated under salt with high concentration but remained unchanged under salt with low concentration. All four clp genes (H1996, H1997, H0950, and H3375) and H3553 gene (which encodes a putative HtrA protease) were significantly induced upon salt stress. These responses support the roles of the housekeeping pathways in both the degradation of damaged proteins induced by salt stress and regulation of proteins involved in the molecular recovery from salt stress. Since serine proteases share several biochemical features and physiological functions, the results from this study provide an insight into diversification of serine proteases in cyanobacteria. Further, these results will increase our understanding of several mechanisms at the subcellular level.

摘要

丝氨酸蛋白酶是一类多功能蛋白水解酶。它们对于蛋白质分解代谢、细胞内氨基酸转换和涉及跨类群的不同分子和细胞过程的蛋白质的调节是必需的。在这项研究中，生物信息学分析揭示了耐盐蓝藻Halothece sp中的大量丝氨酸蛋白酶。PCC7418（以下称为Halothece 7418）与模型淡水蓝藻细长聚球藻PCC7942（以下称为S. elongatus 7942）相比。蓝藻丝氨酸蛋白酶可能来自不同的谱系，因为没有检测到保守的基序。存在高度多样化的丝氨酸蛋白酶Halothece 7418 涉及对几种蛋白酶的进化介导的修饰，这些蛋白酶可能发挥多种生理作用。我们还检查了暴露于盐胁迫的Halothece 7418中 34 个丝氨酸蛋白酶编码基因的基因表达模式。我们的结果表明，几个丝氨酸蛋白酶基因在高浓度盐下显着上调，但在低浓度盐下保持不变。所有四个clp基因（H1996、H1997、H0950和H3375）和​​H3553基因（编码推定的 HtrA 蛋白酶）在盐胁迫下被显着诱导。这些反应支持管家途径在盐胁迫诱导的受损蛋白质降解和参与盐胁迫分子恢复的蛋白质调节中的作用。由于丝氨酸蛋白酶具有多种生化特征和生理功能，因此本研究的结果为蓝藻中丝氨酸蛋白酶的多样化提供了见解。此外，这些结果将增加我们对亚细胞水平的几种机制的理解。