lysylphosphatidylglycerol and alanylphosphatidylglycerol

The bacterial cell membrane accomplishes the controlled exchange of molecules with the extracellular space and mediates specific interactions with the environment. However, the cytoplasmic membrane also includes vulnerable targets for antimicrobial agents. A common feature of cationic antimicrobial peptides (CAMPs) produced by other bacteria or by the host immune system is to utilize the negative charge of bacterial phospholipids such as phosphatidylglycerol (PG) or cardiolipin (CL) for initial adherence and subsequent penetration into the membrane bilayer. To resist cationic antimicrobials many bacteria integrate positive charges into the membrane surface. This is accomplished by aminoacylation of negatively charged (PG) or (CL) with alanine, arginine, or lysine residues. The Multiple Peptide Resistance Factor (MprF) of Staphylococcus aureus is the prototype of a highly conserved protein family of aminoacyl phosphatidylglycerol synthases (aaPGSs) which modify PG or CL with amino acids. MprF is an oligomerizing membrane protein responsible for both, synthesis of lysyl phosphatidylglycerol (LysPG) in the inner leaflet of the cytoplasmic membrane and translocation of LysPG to the outer leaflet. This review focuses on occurrence, synthesis and function of bacterial aminoacyl phospholipids (aaPLs) and on the role of such lipids in basic cellular processes and pathogenicity. This article is part of a Special Issue entitled: Bacterial Lipids edited by Russell E. Bishop.

Topics: Aminoacylation; Animals; Anti-Bacterial Agents; Bacteria; Cell Membrane; Drug Resistance, Bacterial; Host-Pathogen Interactions; Humans; Lipogenesis; Lysine; Molecular Structure; Phosphatidylglycerols; Phospholipids; Signal Transduction; Structure-Activity Relationship

The lysinylation of negatively charged phosphatidylglycerol by MprF proteins reduces the affinity of cationic antimicrobial peptides (CAMPs) for bacterial cytoplasmic membranes and reduces the susceptibility of several Gram-positive bacterial pathogens to CAMPs. MprF of Staphylococcus aureus encompasses a lysyl-phosphatidylglycerol (Lys-PG) synthase and a Lys-PG flippase domain. In contrast, Clostridium perfringens encodes two MprF homologs which specifically synthesize alanyl-phosphatidylglycerol (Ala-PG) or Lys-PG, while only the Lys-PG synthase is fused to a putative flippase domain. It remains unknown whether cationic Lys-PG and zwitterionic Ala-PG differ in their capacities to be translocated by MprF flippases and if both can reduce CAMP susceptibility in Gram-positive bacteria. By expressing the MprF proteins of C. perfringens in an S. aureus mprF deletion mutant, we found that both lipids can be efficiently produced in S. aureus. Simultaneous expression of the Lys-PG and Ala-PG synthases led to the production of both lipids and slightly increased the overall amounts of aminoacyl phospholipids. Ala-PG production by the corresponding C. perfringens enzyme did not affect susceptibility to CAMPs such as nisin and gallidermin or to the CAMP-like antibiotic daptomycin. However, coexpression of the Ala-PG synthase with flippase domains of Lys-PG synthesizing MprF proteins led to a wild-type level of daptomycin susceptibility, indicating that Ala-PG can also protect bacterial membranes against daptomycin and suggesting that Lys-PG flippases can also translocate the related lipid Ala-PG. Thus, bacterial aminoacyl phospholipid flippases exhibit more relaxed substrate specificity and Ala-PG and Lys-PG are more similar in their capacities to modulate membrane functions than anticipated.

Topics: Aminoacyltransferases; Anti-Bacterial Agents; Bacterial Proteins; Biological Transport; Clostridium perfringens; Daptomycin; Lysine; Phosphatidylglycerols; Staphylococcus aureus