Proteome-wide prediction of bacterial carbohydrate-binding proteins as a tool for understanding commensal and pathogen colonisation of the vaginal microbiome

Lectins, such as adhesins and toxins, are carbohydrate-binding proteins that recognise glycans of cells and their secretions. While mediation of microbe-microbe and microbe-host interactions by lectins has long been recognised in the lung and gut, little is known about those in the vagina, where such interactions are implicated in health and various disease states. These include sexually transmitted infections, cervical cancer and poor pregnancy outcomes such as preterm birth. In this study, the curated UniLectin3D database was used to establish a lectin classification based primarily on taxonomy and protein 3D structure. The resulting 109 lectin classes were characterised by specific Hidden Markov Model (HMM) profiles. Screening of microbial genomes in the UniProt and NCBI NR sequence databases resulted in identification of >100 000 predicted bacterial lectins available at unilectin.eu/bacteria. Screening of the complete genomes of 90 isolates from 21 vaginal bacterial species showed that the predicted lectomes (ensemble of predicted lectins) of Lactobacilli associated with vaginal health are substantially less diverse than those of pathogens and pathobionts. Both the number of predicted bacterial lectins, and their specificities for carbohydrates correlated with pathogenicity. This study provides new insights into potential mechanisms of commensal and pathogen colonisation of the reproductive tract that underpin health and disease states.