Decoding the Functional Roles of Cationic Side Chains of the Major Antimicrobial Region of Human Cathelicidin LL-37

Abstract

Human cathelicidin LL-37 is a critical cationic antimicrobial peptide for host defense against infection, immune modulation, and wound healing. This article elucidates the functional roles of the cationic side chains of the major antimicrobial region of LL-37, corresponding to residues 17 to 32 (designated GF-17). Antimicrobial assays, killing kinetics studies, and vesicle leakage experiments all indicate that a conversion of lysines to arginines affected the ability of the peptide to kill the Gram-positive Staphylococcus aureus strain USA300. Alanine scanning experiments show that S. aureus is less sensitive than Escherichia coli to a single cationic residue mutation of GF-17. Among the five cationic residues, R23 appears to be somewhat important in killing S. aureus. However, R23 and K25 of GF-17 are of prime importance in killing the Gram-negative organism E. coli. In particular, R23 is essential for (i) rapid recognition, (ii) permeation of the E. coli outer membrane, (iii) clustering of anionic lipids in a membrane system mimicking the E. coli inner membrane, and (iv) membrane disruption. Bacterial aggregation (i.e., rapid recognition via charge neutralization) is the first step of the peptide action. Structurally, R23 is located in the interface (i.e., the first action layer), a situation ideal for the interactions listed above. In contrast, residues K18, R19, and R29 are on the hydrophilic surface of the amphipathic helix and play only a secondary role. Mapping of the functional spectrum of cationic residues of GF-17 provides a solid basis for engineering bacterium-specific antimicrobials using this highly potent template.

Cationic Antimicrobial Peptide LL-37 Is Effective against both Extra- and Intracellular Staphylococcus aureus

“…It is noteworthy that studies on human cathelicidin analogs reveal that removal of hydrophobic amino acids from the N-terminal end of native LL-37 could decrease its cytotoxicity without compromising the peptide's antimicrobial efficacy toward both Gram-positive and Gram-negative bacteria (78). Wang et al (80) recently mapped and unmasked the potential roles of cationic residues of human cathelicidin LL-37 against different bacterial strains. The cationic side chains of the major antimicrobial region of human cathelicidin LL-37 were fragmented, and their functional roles were studied in detail.…”

“…It also indicated that the conversion of amino acids from lysines (K) to arginines (R) increased the ability of the peptide to kill S. aureus. Therefore, the use of the GF-17 fragment of LL-37 may lead to lower dosages and therefore reduced toxicity (80).…”

Роль Ендогенних Антимікробних Пептидів У Виникненні Пневмонії В Дітей Раннього Віку

“…The ability of Streptococcus of group A to perceive and respond to LL-37 may partially explain the susceptibility of humans as a biological species not only to Streptococcus of group A, but also to streptococcal infection in general [31]. Based on the data obtained, it was suggested that in the conditions of LL-37 deficiency an inversion of its action is observed, that is, instead of the expected bactericidal effect, the virulence of the microorganism increases [35].…”

2-O-Sulfated Domains in Syndecan-1 Heparan Sulfate Inhibit Neutrophil Cathelicidin and Promote Staphylococcus aureus Corneal Infection

“…A particular binding site in CRAMP may directly bind to 2-O-sulfated uronic acids in syndecan-1 HS or bind to a conformation of syndecan-1 HS that is dictated by 2-O-sulfated motifs. In fact, spacing of cationic amino acids is important for the anti-bacterial activity of LL-37 (61), suggesting that similar spacing of cationic residues in CRAMP may allow this peptide to avidly bind to 2-O-sulfate motifs in syndecan-1 HS.…”