title: The structural parameters for antimicrobial activity, human epithelial cell cytotoxicity and killing mechanism of synthetic monomer and dimer analogues derived from hBD3 C-terminal region.
abstract: Understanding the molecular mechanisms of antimicrobial peptide-membrane interactions is crucial in predicting the design of useful synthetic antimicrobial peptide analogues. Defensins are small (3-5 kDa) cysteine-rich cationic proteins which constitute the front line of host innate immunity. In this study, a series of eight 10 AA C-terminal analogues of hBD3 [sequence: RGRKXXRRKK, X = W, F, Y, V, L, I, H, C(Acm); net charge = +7, coded as W2, F2, Y2, V2, L2, I2, H2, and C2] and covalent V2-dimer [(RGRKVVRR)(2)KK] (18 AA, net charge = +11) were synthesized using solid phase peptide synthesis (SPPS) in Fmoc chemistry. Wild-type hBD3 was used as a control in all analyses. W2, V2, and especially Y2 showed high activity selectively against Gram-negative bacteria Pseudomonas aeruginosa in the concentration range of 4.3-9.7 microM. The covalent dimeric form of V2-monomer, V2-dimer, showed increased antibacterial killing compared to the monomeric form, V2-monomer. Cytotoxicity assays on a human conjunctival epithelial cell line (IOBA-NHC cells) showed that no change in viable cell number 24 h after constant exposure to all the eight peptide analogues even at concentrations up to 200 microg/ml. Fluorescence correlation spectroscopy (FCS) was used to study the interaction of these peptides against POPC vesicles (neutral; mammalian cell membrane mimic) and POPG vesicles (negatively charged; bacterial cell membrane mimic). Using FCS, significant aggregation and some leakage of Rhodamine dye were observed with POPG with Y2, W2 and V2 at the concentration of 5-10 mmicroM and no significant aggregation or disruption of vesicles was observed for all peptide analogues tested against POPC. V2-dimer induced more leakage and aggregation than the monomeric form. Overall, V2-dimer is the most effective antimicrobial peptide, with aggregation of POPG vesicles observed at concentrations as low as 1 microM. The concentration of 5-10 microM for Y2 from FCS correlated with the concentration of 5 microM (6.25 microg/ml), at which Y2 showed a cooperative increase in the activity. This suggests a structural transition of Y2 in the 2.5-5 microM concentration range resulting in the correlated increased antimicrobial activity. These results and the FCS together with previous NMR and molecular dynamics (MD) suggested that the charge density-based binding affinity, stable covalent dimerization, the ability to dimerize or even oligomerize and adopt a well-defined structure are important physicochemical properties distinguishing more effective cationic antimicrobial peptides.
authors.affiliation: Singapore Eye Research Institute, Singapore, Singapore.
authors.forename: L
authors.initials: L
authors.lastname: Zhou
authors.forename: S P
authors.initials: SP
authors.lastname: Liu
authors.forename: L Y
authors.initials: LY
authors.lastname: Chen
authors.forename: J
authors.initials: J
authors.lastname: Li
authors.forename: L B
authors.initials: LB
authors.lastname: Ong
authors.forename: L
authors.initials: L
authors.lastname: Guo
authors.forename: T
authors.initials: T
authors.lastname: Wohland
authors.forename: C C
authors.initials: CC
authors.lastname: Tang
authors.forename: R
authors.initials: R
authors.lastname: Lakshminarayanan
authors.forename: J
authors.initials: J
authors.lastname: Mavinahalli
authors.forename: C
authors.initials: C
authors.lastname: Verma
authors.forename: R W
authors.initials: RW
authors.lastname: Beuerman
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000494:pharmacology*; D002460:Cell Line; D003603:Cytotoxins / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*; D019281:Dimerization; D004847:Epithelial Cells / Q000187:drug effects*; D006090:Gram-Negative Bacteria / Q000187:drug effects; D006801:Humans; D015394:Molecular Structure; D023083:beta-Defensins / Q000138:chemical synthesis / Q000737:chemistry* / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D003603:Cytotoxins; C422950:DEFB103A protein, human; D023083:beta-Defensins