In Silico Identification and Characterization of a Hypothetical Protein From Rhodobacter capsulatus Revealing S-Adenosylmethionine-Dependent Methyltransferase Activity

Rhodobacter capsulatus is a purple non-sulfur bacteria widely used as a model organism to study bacterial photosynthesis. It exhibits extensive metabolic activities and demonstrates other distinctive characteristics such as pleomorphism and nitrogen-fixing capability. It can act as a gene transfer agent (GTA). The commercial importance relies on producing polyester polyhydroxyalkanoate (PHA), extracellular nucleic acids, and commercially critical single-cell proteins. These diverse features make the organism an exciting and environmentally and industrially important one to study. This study was aimed to characterize, model, and annotate the function of a hypothetical protein (Accession no. CAA71016.1) of R capsulatus through computational analysis. The urf7 gene encodes the protein. The tertiary structure was predicted through MODELLER and energy minimization and refinement by YASARA Energy Minimization Server and GalaxyRefine tools. Analysis of sequence similarity, evolutionary relationship, and exploration of domain, family, and superfamily inferred that the protein has S-adenosylmethionine (SAM)-dependent methyltransferase activity. This was further verified by active site prediction by CASTp server and molecular docking analysis through Autodock Vina tool and PatchDock server of the predicted tertiary structure of the protein with its ligands (SAM and SAH). Normally, as a part of the gene product of photosynthetic gene cluster (PGC), the established roles of SAM-dependent methyltransferases are bacteriochlorophyll and carotenoid biosynthesis. But the STRING database unveiled its association with NADH-ubiquinone oxidoreductase (Complex I). The assembly and regulation of this Complex I is mediated by the gene products of the nuo operon. As a part of this operon, the urf7 gene encodes SAM-dependent methyltransferase. As a consequence of these findings, it is reasonable to propose that the hypothetical protein of interest in this study is a SAM-dependent methyltransferase associated with bacterial NADH-ubiquinone oxidoreductase assembly. Due to conservation of Complex I from prokaryotes to eukaryotes, R capsulatus can be a model organism of study to understand the common disorders which are linked to the dysfunctions of complex I.