Modeling and computational characterization of a sp. Hypothetical protein identifies a remote ortholog of lethal factor 1.

Lethal Factor 1 (BLF1) is a deamidase first characterized in . This enzyme inhibits cellular protein synthesis by deamidating a glutamine residue to a glutamic acid in its target protein, the eukaryotic translation initiation factor 4 A (eIF4A). In this work, we present the characterization of a hypothetical protein from sp. Leaf131 as the first report of a BLF1 family ortholog outside of the genus. Although standard sequence similarity searches such as BLAST were not able to detect the homology between the sp. Leaf131 hypothetical protein sequence and BLF1, our computed structure model for the sp. hypothetical protein revealed structural similarities with an RMSD of 2.7 Å/164 Cα atoms and a TM-score of 0.72 when superposed. Structural comparisons of the model structure against BLF1 and cytotoxic necrotizing factor 1 (CNF1) revealed that the conserved signature LXGC motif and putative catalytic residues are structurally aligned thus signifying a level of functional or mechanistic similarity. Protein-protein docking analysis and molecular dynamics simulations also demonstrated that eIF4A could still be a possible target substrate for deamidation by XLF1 as it is for BLF1. We therefore propose that this hypothetical protein be renamed as Lethal Factor 1 (XLF1). Our work also provides further evidence of the utility of programs such as AlphaFold in bridging the computational function annotation transfer gap despite very low sequence identities of under 20%.Communicated by Ramaswamy H. Sarma.