C-Terminal Amino Acids of Alpha-Melanocyte-Stimulating Hormone Are Requisite for Its Antibacterial Activity against Staphylococcus aureus

Abstract

Alpha-melanocyte-stimulating hormone (␣-MSH) is an endogenous neuropeptide that is known for its anti-inflammatory and antipyretic activities.We recently demonstrated that ␣-MSH possesses staphylocidal activity and causes bacterial membrane damage. To understand the role of its amino acid sequences in the staphylocidal mechanism, in the present study we investigated the antimicrobial activities of different fragments of ␣-MSH, i.e., ␣-MSH(6-13), ␣-MSH(11-13), and ␣-MSH(1-5), and compared them with that of the entire peptide. Our results showed that peptides containing the C-terminal region of ␣-MSH, namely, ␣-MSH(6-13) and ␣-MSH(11-13), efficiently killed >90% of both methicillin-sensitive and -resistant Staphylococcus aureus cells in the micromolar range and ϳ50% of these cells in the nanomolar range; their efficiency was comparable to that of the entire ␣-MSH, whereas the peptide containing the N-terminal region, ␣-MSH(1-5), was found to be ineffective against S. aureus. The antimicrobial activity of ␣-MSH and its C-terminal fragments was not affected by the presence of NaCl or even divalent cations such as Ca 2؉ and Mg 2؉ . Similar to the case for the parent peptide, ␣-MSH(6-13) and ␣-MSH(11-13) also depolarized and permeabilized Staphylococcus cells (ϳ70 to 80% of the cells were depolarized and lysed after 2 h of peptide exposure at micromolar concentrations). Furthermore, scanning and transmission electron microscopy showed remarkable morphological and ultrastructural changes on S. aureus cell surface due to exposure to ␣-MSH-based peptides. Thus, our observations indicate that C-terminal fragments of ␣-MSH retain the antimicrobial activity of entire peptide and that their mechanism of action is similar to that of full-length peptide. These observations are important and are critical in the rational design of ␣-MSH-based therapeutics with optimal efficacy.

Combination of Alpha-Melanocyte Stimulating Hormone with Conventional Antibiotics against Methicillin Resistant Staphylococcus aureus

“…We have earlier established the strong antibacterial activity of alpha-melanocyte stimulating hormone (α-MSH) and its congeners containing C-terminal amino acids against both reference and clinical isolates of Staphylococcus aureus ( S. aureus ) [21]–[23]. Subsequently, we confirmed that the staphylocidal action of α-MSH occurred due to depolarization and permeabilization of the bacterial membrane [22], [23].…”

Differential Adaptive Responses of Staphylococcus aureus to In Vitro Selection with Different Antimicrobial Peptides

“…After every 5 transfers, evolution of resistance in the positive-selection line against magainin 2 and gramicidin D was identified by determining the MIC in MHB, following NCCLS guidelines (14). Further confirmation of resistance was done by performing a bactericidal assay as described before (15,16).The development of resistance occurred for both of the AMPs studied, as indicated by a gradual rise in MIC values with increasing passage number in the positive-selection lines compared to the MICs in the respective control selection lines. At the 55th passage, the positive-selection strains showed an Ն8-and a 128-fold increase in MIC value for magainin 2 (strain 55MG) and gramicidin D (strain 55GR), respectively, compared to the MIC of the control (Fig.…”

“…After every 5 transfers, evolution of resistance in the positive-selection line against magainin 2 and gramicidin D was identified by determining the MIC in MHB, following NCCLS guidelines (14). Further confirmation of resistance was done by performing a bactericidal assay as described before (15,16).…”

Alpha-Melanocyte Stimulating Hormone: An Emerging Anti-Inflammatory Antimicrobial Peptide

“…It is interesting to note that the antimicrobial activity of α -MSH and its C-terminal fragments— α -MSH(6–13) (HFRWGKPV) and α -MSH(11–13) (KPV)—remains intact even in the presence of salts at their physiological concentrations, namely, NaCl (150 mM), CaCl 2 (2 mM), and MgCl 2 (1 mM) [18]. More recently, it has been suggested that α -MSH acts synergistically with antibiotics belonging to different classes.…”