Functional and Structural Analysis of a Novel Acyltransferase from Pathogenic Phytophthora melonis

This investigation characterizes an acyltransferase enzyme responsible for the pathogenicity of Phytophthora melonis. The protein was characterized in vitro for its physicochemical properties. The biochemical characterization, including thermal and pH stability, revealed the 35 °C temperature and 7.0 pH as the optimum conditions for the enzyme. Applying the Tween-80 solution enhanced the activity up to 124.9%. Comprehensive structural annotation revealed two domains, A (ranging from residues 260 to 620) and B (ranging from 141 to 219). Domain A had transglutaminase (T-Gase) elicitor properties, while B possessed antifreeze features. Rigorous sequence characterization of the acyltransferase tagged it as a low-temperature-resistant protein. Further, the taxonomic distribution analysis of the protein highlighted three genera in Oomycetes, i.e., Pythium, Phytophthora, and Plasmopara, bearing this protein. However, some taxonomic groups other than Oomycetes (i.e., archaea and bacteria) also contained the protein. Functional studies of structurally analogous proteins spanned 10 different taxonomic groups. These revealed TGase elicitors (10%), phytopathogen effector proteins RxLR (4%), transporter family proteins (3%), and endonucleases (1%). Other analogues having one percent of their individual share were HIV tat-specific factor 1, protocadherin fat 4, transcription factor 1, and 3-hydroxyisobutyrate dehydrogenase. Because the plant infection by P. melonis is a complex process regulated by a profusion of extracellular signals secreted by both host plants and the pathogen, this study will be of help in interpreting the cross-talk in the host-pathogen system.