title: D-alanylation of lipoteichoic acids confers resistance to cationic peptides in group B streptococcus by increasing the cell wall density.
abstract: Cationic antimicrobial peptides (CAMPs) serve as the first line of defense of the innate immune system against invading microbial pathogens. Gram-positive bacteria can resist CAMPs by modifying their anionic teichoic acids (TAs) with D-alanine, but the exact mechanism of resistance is not fully understood. Here, we utilized various functional and biophysical approaches to investigate the interactions of the human pathogen Group B Streptococcus (GBS) with a series of CAMPs having different properties. The data reveal that: (i) D-alanylation of lipoteichoic acids (LTAs) enhance GBS resistance only to a subset of CAMPs and there is a direct correlation between resistance and CAMPs length and charge density; (ii) resistance due to reduced anionic charge of LTAs is not attributed to decreased amounts of bound peptides to the bacteria; and (iii) D-alanylation most probably alters the conformation of LTAs which results in increasing the cell wall density, as seen by Transmission Electron Microscopy, and reduces the penetration of CAMPs through the cell wall. Furthermore, Atomic Force Microscopy reveals increased surface rigidity of the cell wall of the wild-type GBS strain to more than 20-fold that of the dltA mutant. We propose that D-alanylation of LTAs confers protection against linear CAMPs mainly by decreasing the flexibility and permeability of the cell wall, rather than by reducing the electrostatic interactions of the peptide with the cell surface. Overall, our findings uncover an important protective role of the cell wall against CAMPs and extend our understanding of mechanisms of bacterial resistance.
authors.affiliation: Department of Biological Chemistry, The Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Ron
authors.initials: R
authors.lastname: Saar-Dover
authors.forename: Arkadi
authors.initials: A
authors.lastname: Bitler
authors.forename: Ravit
authors.initials: R
authors.lastname: Nezer
authors.forename: Liraz
authors.initials: L
authors.lastname: Shmuel-Galia
authors.forename: Arnaud
authors.initials: A
authors.lastname: Firon
authors.forename: Eyal
authors.initials: E
authors.lastname: Shimoni
authors.forename: Patrick
authors.initials: P
authors.lastname: Trieu-Cuot
authors.forename: Yechiel
authors.initials: Y
authors.lastname: Shai
mesh_terms: D000409:Alanine / Q000378:metabolism* / Q000494:pharmacology; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D023181:Antimicrobial Cationic Peptides / Q000494:pharmacology*; D002473:Cell Wall / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D004352:Drug Resistance, Microbial / Q000187:drug effects / Q000502:physiology; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D018625:Microscopy, Atomic Force; D046529:Microscopy, Electron, Transmission; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D011499:Protein Processing, Post-Translational / Q000502:physiology; D013290:Streptococcal Infections / Q000382:microbiology; D013291:Streptococcus / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D013499:Surface Properties; D013682:Teichoic Acids / Q000378:metabolism* / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D023181:Antimicrobial Cationic Peptides; D008070:Lipopolysaccharides; D013682:Teichoic Acids; C009900:lipoteichoic acid; D000409:Alanine