Multiple sequence alignment of homoserine-acetyltransferases, serine-acetyltransferases and homoserine-succinyltransferases show they all belong to MetX family, having evolved from a common ancestor by conserving the catalytic site and substrate binding residues. The discrimination in the substrate selection arises due to the presence of substrate-specific residues lining the substrate-binding pocket. Mutation of Ala59 and Gly62 to Gly and Pro respectively in homoserine-acetyltransferase from M. tuberculosis resulted in a serine-acetyltransferase like enzyme as it acetylated both l-homoserine and l-serine. Homoserine-acetyltransferase from M. tuberculosis when mutated at positon 322 where Leu was converted to Arg, resulted in succinylation over acetylation of l-homoserine. Our studies establish the importance of the substrate binding residues in determining the type of activity possessed by MetX family, despite all of them having the same catalytic triad Ser-Asp-His. Hence key residues at the substrate binding pocket dictate whether the given enzyme shows predominant transferase or hydrolase activity.

高丝氨酸-乙酰转移酶、丝氨酸-乙酰转移酶和高丝氨酸-琥珀酰基转移酶的多序列比对表明它们都属于 MetX 家族，通过保留催化位点和底物结合残基从共同祖先进化而来。由于底物结合袋内衬底物特异性残基的存在，底物选择中的歧视出现。在来自结核分枝杆菌的高丝氨酸-乙酰转移酶中，Ala59 和 Gly62 分别突变为 Gly 和 Pro，导致丝氨酸-乙酰转移酶样酶，因为它乙酰化l-高丝氨酸和l-丝氨酸。来自结核分枝杆菌的高丝氨酸乙酰转移酶当在 Leu 转化为 Arg 的 322 位发生突变时，导致琥珀酰化超过l-高丝氨酸的乙酰化。我们的研究确定了底物结合残基在确定 MetX 家族拥有的活性类型方面的重要性，尽管它们都具有相同的催化三联体 Ser-Asp-His。因此，底物结合口袋处的关键残基决定了给定的酶是否显示出主要的转移酶或水解酶活性。