Bioinformatic pipeline for functional inference of Rickettsia akari hypothetical proteins reveals virulence-associated and effector candidates

Background Rickettsia akari, the causative agent of rickettsialpox, is an obligate intracellular pathogen with a highly reduced genome encoding numerous hypothetical proteins (HPs) of unknown function. Many of these HPs are expressed during host-cell infection, yet their roles in bacterial physiology and potential contribution to virulence remain unclear. Methodology/Principal Findings We performed an integrative in silico characterization of 54 R. akari HPs previously identified by mass spectrometry in purified bacterial cells. Using a benchmarked computational workflow, we predicted their physicochemical properties, subcellular localization, putative secretion signals, protein folds, potential interaction partners, and evolutionary conservation. Most HPs were predicted to be thermostable. The majority of HPs were predicted to be cytoplasmic (37.00%) or membrane-associated (29.63%). Predicted features associated with the type IV secretion system were more frequent than those associated with type I secretion. Network and structural analyses identified candidate HPs with features consistent with potential roles in outer membrane assembly, host-cell interaction, and immune modulation, including predicted peptidyl-prolyl cis/trans isomerases, oxidoreductases, methyltransferases, and putative E3 ubiquitin ligases. Several HPs were predicted to be antigenic and showed conservation across multiple rickettsial genomes. Molecular docking and normal mode analysis supported the plausibility of selected predicted protein-protein and protein-ligand interactions. Evolutionary analyses indicated predominant purifying selection among the analyzed HPs. A8GP20 showed elevated sequence divergence and warrants further investigation as a potential effector candidate. Conclusions/Significance Our findings prioritize A8GPG8, A8GP63, A8GNV4, A8GMM8, A8GM41, A8GMJ7, A8GMI5, A8GP20, A8GN23, A8GMB4, A8GM08, and A8GM39 as promising candidates for experimental validation of their predicted functions and potential roles in R. akari biology and pathogenicity. This work provides an integrative and reproducible bioinformatic framework to guide functional discovery in R. akari and related neglected intracellular pathogens, and identifies candidate proteins for future studies of rickettsial pathogenesis, antigen discovery, and therapeutic target development.