CSIR-Institute of Microbial Technology, Sector 39-A, Chandigarh, 160036, India.
Institute of Forensic Science &Criminology, Panjab University, Sector 14, Chandigarh, 160014, India.
Sci Rep. 2016 Jun 29;6:28892. doi: 10.1038/srep28892.
Nα-acetylation is a naturally occurring irreversible modification of N-termini of proteins catalyzed by Nα-acetyltransferases (NATs). Although present in all three domains of life, it is little understood in bacteria. The functional grouping of NATs into six types NatA - NatF, in eukaryotes is based on subunit requirements and stringent substrate specificities. Bacterial orthologs are phylogenetically divergent from eukaryotic NATs, and only a couple of them are characterized biochemically. Accordingly, not much is known about their substrate specificities. Rv3420c of Mycobacterium tuberculosis is a NAT ortholog coding for RimI(Mtb). Using in vitro peptide-based enzyme assays and mass-spectrometry methods, we provide evidence that RimI(Mtb) is a protein Nα-acetyltransferase of relaxed substrate specificity mimicking substrate specificities of eukaryotic NatA, NatC and most competently that of NatE. Also, hitherto unknown acetylation of residues namely, Asp, Glu, Tyr and Leu by a bacterial NAT (RimI(Mtb)) is elucidated, in vitro. Based on in vivo acetylation status, in vitro assay results and genetic context, a plausible cellular substrate for RimI(Mtb) is proposed.
Nα-乙酰化是一种由 Nα-乙酰转移酶（NATs）催化的蛋白质 N 末端的自然发生的不可逆修饰。尽管存在于所有三个生命领域中，但在细菌中却知之甚少。真核生物中 NAT 分为 6 种类型 NatA-NatF，这是基于亚基要求和严格的底物特异性进行的功能分组。细菌的同源物与真核 NAT 在系统发育上有很大的差异，只有少数几个在生化上有特征。因此，它们的底物特异性知之甚少。结核分枝杆菌的 Rv3420c 是编码 RimI（Mtb）的 NAT 同源物。通过体外基于肽的酶测定和质谱方法，我们提供了证据表明 RimI（Mtb）是一种具有宽松底物特异性的蛋白质 Nα-乙酰转移酶，模拟了真核 NatA、NatC 的底物特异性，最能模拟 NatE 的底物特异性。此外，还在体外阐明了细菌 NAT（RimI（Mtb））对残基天冬氨酸、谷氨酸、酪氨酸和亮氨酸的未知乙酰化。基于体内乙酰化状态、体外测定结果和遗传背景，提出了 RimI（Mtb）的一个合理的细胞底物。
