Prediction driven functional annotation of hypothetical proteins in the major facilitator superfamily of S. aureus NCTC 8325

Antibiotic resistance Staphylococcus aureus strains cause several life threatening infections. New drug treatment options are needed, but are slow to develop because 50% of the S. aureus genome is hypothetical. The goal of this is to aid in the annotation of the S. aureus NCTC 8325 genome by identifying hypothetical proteins related to the Major Facilitator Superfamily (MFS). The MFS is a broad protein group with members involved in drug efflux mechanisms causing resistance. To do this, sequences for three MFS proteins with x-ray crystal structures in E. coli were PSI-BLASTed against the S. aureus NCTC 8325 genome to identify homologs. Eleven identified hypothetical protein homologs underwent BLASTP against the non-redundant NCBI database to fit homologs specific to each hypothetical protein. ExPASy characterized the physiochemical features, CDD-BLAST and Pfam identified domains, and the SOSUI server defined transmembrane helices of each hypothetical protein. Based on size (300 - 700 amino acids), number of transmembrane helices (>7), CD06174 and MFS domains in CDD-BLAST and Pfam, respectively, and close relation to well-defined homologs, SAOUHSC_00058, SAOUHSC_00078, SAOUHSC_00952, SAOUHSC_02435, SAOUHSC_02752, and ABD31642.1 are members of the MFS. Further multiple-alignment and phylogeny analyses show SAOUHSC_00058 to be a quinolone resistance protein (NorB), SAOUHSC_00058 a siderophore biosynthesis protein (SbnD), SAOUHSC_00952 a glycolipid permease (LtaA), SAOUHSC_02435 a macrolide MFS transporter, SAOUHSC_02752 a chloramphenicol resistance (DHA1), and ABD31642.1 is a Bcr/CflA family drug resistance efflux transporter. These findings provide better annotation for the existing genome, and identify proteins related to antibiotic resistance in S. aureus NCTC 8325.