155. Structural homologs of Enterococcus faecalis LiaX-like genes in Bacillus subtilis provides new insights into the LiaFSR-mediated response associated with daptomycin resistance


 
 
 VRE (Vancomycin Resistant Enterococci)-associated infections are prevalent in healthcare settings and pose a significant therapeutic challenge. The lipopeptide antimicrobial daptomycin (DAP) is one of the last resort options to treat these organisms. Among VRE, mutations that confer DAP resistance (DAP-R) arise in proteins in the three-component signaling system LiaFSR, which is highly conserved in other Gram-positive pathogens. Similar to Enterococcus faecalis (Efs), LiaFSR in Bacillus subtilis (Bsu) is specifically activated by DAP and, thus, serves as a proxy for studying mechanisms of DAP-R. In Bsu, LiaF inhibits LiaR phosphorylation; however, the current model for DAP-R in Efs positions LiaF as an activator of LiaFSR directly regulated by the enterococcal-specific protein LiaX. We postulate that the intimate association between LiaX and LiaF is crucial for DAP-R in enterococci. Using an in silico approach, we compared LiaF from Efs and Bsu and searched for LiaX-like proteins in Bsu.
 
 
 
 Protein predictions were determined by the RoseTTAFold algorithm (RoBetta, David Baker, UW). Structural comparisons were conducted using MatchMaker in UCSF Chimera. Paired sequence alignments were assembled through EMBOSS Needle.
 
 
 
 Efs and Bsu LiaF are arranged similarly with 4 transmembrane helices (TMH) in the N-terminal domain (NTD) and a β-sheet (βS) C-terminal domain (CTD). We identified LiaX-like gene products upstream from Bsu LiaFSR. Analysis of the predicted structures of LiaIHG showed that LiaI is a peptide with 4 TMH and structurally like the N-terminus of Bsu LiaF. Also, LiaH contains 3 putative α-helices akin to the N-terminus of LiaX. LiaG has 1 TMH connected to a large βS domain-like the C-terminus of LiaX. Each protein shared structural and sequence similarity that was not identified through BLAST searches.
 
 
 
 We identified Bsu LiaIHG as structural homologs to Efs LiaX, which was not previously known due to lack of sequence identity and empirical structural data. The findings further supports our model for LiaX and LiaF as core pieces in DAP-R development.
 
 
 
 Cesar A. Arias, MD, PhD, Entasis Phramceuticals: Grant/Research Support|MeMed Diagnostics: Grant/Research Support|Merck: Grant/Research Support.
