New sub-family of lysozyme-like proteins shows no catalytic activity: crystallographic and biochemical study of STM3605 protein from Salmonella Typhimurium.
New sub-family of lysozyme-like proteins shows no catalytic activity: crystallographic and biochemical study of STM3605 protein from Salmonella Typhimurium.
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DOI：
10.1007/s10969-013-9151-0
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发表时间：
2013-03
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通讯作者：
Joachimiak, Andrzej
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作者：
Michalska, Karolina;Brown, Roslyn N;Li, Hui;Jedrzejczak, Robert;Niemann, George S;Heffron, Fred;Cort, John R;Adkins, Joshua N;Babnigg, Gyorgy;Joachimiak, Andrzej
感染原核生物的噬菌体病毒将其基因组整合到宿主染色体中；因此，微生物基因组通常包含现代和古代噬菌体感染的遗传残留物。通常，噬菌体基因出现在反映外源DNA整合的非典型G+C内容簇中。然而，一些噬菌体基因是在没有其他噬菌体基因邻居的情况下孤立出现的，可能是水平基因转移造成的。在这些情况下，噬菌体基因产物不太可能作为成熟噬菌体颗粒的组成部分发挥作用，相反，可能被宿主出于自身的利益而增选。来自鼠伤寒沙门氏菌的一个这样的基因产物STM3605编码一个与噬菌体样溶菌酶(N-乙酰溶菌酰胺酶)有适度序列相似性的蛋白质，但似乎缺乏在所有溶菌酶中严格保守的必要催化残基。其他细菌中的紧密同源物也具有这一特征。X-射线结晶学分析表明，STM3605蛋白是一种稳定的折叠蛋白，其结构与溶菌酶相似。然而，这种蛋白质不太可能水解肽聚糖。相反，STM3605被认为进化了另一种功能，因为它显示出一些裂解活性和对胶束的分配。
Phage viruses that infect prokaryotes integrate their genome into the host chromosome; thus, microbial genomes typically contain genetic remnants of both recent and ancient phage infections. Often phage genes occur in clusters of atypical G+C content that reflect integration of the foreign DNA. However, some phage genes occur in isolation without other phage gene neighbors, probably resulting from horizontal gene transfer. In these cases, the phage gene product is unlikely to function as a component of a mature phage particle, and instead may have been co-opted by the host for its own benefit. The product of one such gene from Salmonella enterica serovar Typhimurium, STM3605, encodes a protein with modest sequence similarity to phage-like lysozyme (N-acetylmuramidase) but appears to lack essential catalytic residues that are strictly conserved in all lysozymes. Close homologs in other bacteria share this characteristic. The structure of the STM3605 protein was characterized by X-ray crystallography, and functional assays showed that it is a stable, folded protein whose structure closely resembles lysozyme. However, this protein is unlikely to hydrolyze peptidoglycan. Instead, STM3605 is presumed to have evolved an alternative function because it shows some lytic activity and partitions to micelles.