Macropin 1

The abuse of antibiotics for disease treatment has led to the emergence of multidrug resistant bacteria. Antimicrobial peptides, found naturally in various organisms, have received increasing interest as alternatives to conventional antibiotics because of their broad spectrum antimicrobial activity and low cytotoxicity. In a previous report, Macropin, isolated from bee venom, exhibited antimicrobial activity against both gram-positive and negative bacteria. In the present study, Macropin was synthesized and its antibacterial and anti-biofilm activities were tested against bacterial strains, including gram-positive and negative bacteria, and drug resistant bacteria. Moreover, Macropin did not exhibit hemolytic activity and cytotoxicity to keratinocytes, whereas Melittin, as a positive control, showed very high toxicity. Circular dichroism assays showed that Macropin has an α-helical structure in membrane mimic environments. Macropin binds to peptidoglycan and lipopolysaccharide and kills the bacteria by disrupting their membranes. Moreover, the fractional inhibitory concentration index indicated that Macropin has additive and partially synergistic effects with conventional antibiotics against drug resistant bacteria. Thus, our study suggested that Macropin has potential for use of an antimicrobial agent for infectious bacteria, including drug resistant bacteria.

A novel antimicrobial peptide, designated macropin (MAC-1) with sequence Gly-Phe-Gly-Met-Ala-Leu-Lys-Leu-Leu-Lys-Lys-Val-Leu-NH2 , was isolated from the venom of the solitary bee Macropis fulvipes. MAC-1 exhibited antimicrobial activity against both Gram-positive and Gram-negative bacteria, antifungal activity, and moderate hemolytic activity against human red blood cells. A series of macropin analogs were prepared to further evaluate the effect of structural alterations on antimicrobial and hemolytic activities and stability in human serum. The antimicrobial activities of several analogs against pathogenic Pseudomonas aeruginosa were significantly increased while their toxicity against human red blood cells was decreased. The activity enhancement is related to the introduction of either l- or d-lysine in selected positions. Furthermore, all-d analog and analogs with d-amino acid residues introduced at the N-terminal part of the peptide chain exhibited better serum stability than did natural macropin. Data obtained by CD spectroscopy suggest a propensity of the peptide to adopt an amphipathic α-helical secondary structure in the presence of trifluoroethanol or membrane-mimicking sodium dodecyl sulfate. In addition, the study elucidates the structure-activity relationship for the effect of d-amino acid substitutions in MAC-1 using NMR spectroscopy.

Anticancer peptides (ACPs) could potentially offer many advantages over other cancer therapies. ACPs often target cell membranes, where their surface mechanism is coupled to a conformational change into helical structures. However, details on their binding are still unclear, which would be crucial to reach progress in connecting structural aspects to ACP action and to therapeutic developments. Here we investigated natural helical ACPs, Lasioglossin LL-III, Macropin 1, Temporin-La, FK-16, and LL-37, on model liposomes, and also on extracellular vesicles (EVs), with an outer leaflet composition similar to cancer cells. The combined simulations and experiments identified three distinct binding modes to the membranes. Firstly, a highly helical structure, lying mainly on the membrane surface; secondly, a similar, yet only partially helical structure with disordered regions; and thirdly, a helical monomeric form with a non-inserted perpendicular orientation relative to the membrane surface. The latter allows large swings of the helix while the N-terminal is anchored to the headgroup region. These results indicate that subtle differences in sequence and charge can result in altered binding modes. The first two modes could be part of the well-known carpet model mechanism, whereas the newly identified third mode could be an intermediate state, existing prior to membrane insertion.