Alyteserin-1c (GLKEIFKAGLGSLVKGIAAHVAS.NH(2)), first isolated from skin secretions of the midwife toad Alytes obstetricans, shows selective growth-inhibitory activity against Gram-negative bacteria. The structures of alyteserin-1c and its more potent and less haemolytic analogue [E4K]alyteserin-1c were investigated in various solution and membrane mimicking environments by proton NMR spectroscopy and molecular modelling. In aqueous solution, the peptide displays a lack of secondary structure but, in a 2,2,2-trifluoroethanol (TFE-d(3))-H(2)O solvent mixture, the structure is characterised by an extended alpha helix between residues Leu(2) and Val(21). Solution structural studies in the membrane mimicking environments, sodium dodecyl sulphate (SDS), dodecylphosphocholine (DPC), and 1,2-dihexanoyl-sn-glycero-3-phosphatidylcholine (DHPC) micelles, indicate that these peptides display an alpha helical structure between residues Lys(3) and Val(21). Positional studies of the peptides in SDS, DPC and DHPC media show that the N-terminal and central residues lie inside the micelle while C-terminal residues beyond Ala(19) do not interact with the micelles.

Brevinin‐1BYa (FLPILASLAAKFGPKLFCLVTKKC), first isolated from skin secretions of the foothill yellow‐legged frog Rana boylii, shows broad‐spectrum activity, being particularly effective against opportunistic yeast pathogens. The structure of brevinin‐1BYa was investigated in various solution and membrane‐mimicking environments by proton nuclear magnetic resonance (1H‐NMR) spectroscopy and molecular modelling. The peptide does not possess a secondary structure in aqueous solution. In a 33% 2,2,2‐trifluoroethanol (TFE‐d3)‐H2O solvent mixture, as well as in membrane‐mimicking sodium dodecyl sulfate and dodecylphosphocholine micelles, the peptide's structure is characterised by a flexible helix‐hinge‐helix motif, with the hinge located at the Gly13/Pro14 residues, and the two α‐helices extending from Pro3 to Phe12 and from Pro14 to Thr21. Positional studies involving the peptide in sodium dodecyl sulfate and dodecylphosphocholine micelles using 5‐doxyl‐labelled stearic acid and manganese chloride paramagnetic probes show that the peptide's helical segments lie parallel to the micellar surface, with the residues on the hydrophobic face of the amphipathic helices facing towards the micelle core and the hydrophilic residues pointing outwards, suggesting that the peptide exerts its biological activity by a non–pore‐forming mechanism.

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Ablation of glucagon receptor signaling represents a potential treatment option for type 2 diabetes (T2DM). Additionally, activation of glucose-dependent insulinotropic polypeptide (GIP) receptor signaling also holds therapeutic promise for T2DM. Therefore, this study examined both independent and combined metabolic actions of desHis 1 Pro 4 Glu 9 (Lys 12 PAL)-glucagon (glucagon receptor antagonist) and d-Ala 2 GIP (GIP receptor agonist) in diet-induced obese mice. Glucagon receptor binding has been linked to alpha-helical structure and desHis 1 Pro 4 Glu 9 (Lys 12 PAL)-glucagon displayed enhanced alpha-helical content compared with native glucagon. In clonal pancreatic BRIN-BD11 beta-cells, desHis 1 Pro 4 Glu 9 (Lys 12 PAL)-glucagon was devoid of any insulinotropic or cAMP-generating actions, and did not impede d-Ala 2 GIP-mediated (P < 0.01 to P < 0.001) effects on insulin and cAMP production. Twice-daily injection of desHis 1 Pro 4 Glu 9 (Lys 12 PAL)-glucagon or d-Ala 2 GIP alone, and in combination, in highfat-fed mice failed to affect body weight or energy intake. Circulating blood glucose levels were significantly (P < 0.05 to P < 0.01) decreased by all treatments regimens, with plasma and pancreatic insulin elevated (P < 0.05 to P < 0.001) in all mice receiving d-Ala 2 GIP. Interestingly, plasma glucagon concentrations were decreased (P < 0.05) by sustained glucagon inhibition (day 28), but increased (P < 0.05) by d-Ala 2 GIP therapy, with a combined treatment resulting in glucagon concentration similar to saline controls. All treatments improved (P < 0.01) intraperitoneal and oral glucose tolerance, and peripheral insulin sensitivity. d-Ala 2 GIP-treated mice showed increased glucoseinduced insulin secretion in response to intraperitoneal and oral glucose. Metabolic rate and ambulatory locomotor activity were increased (P < 0.05 to P < 0.001) in all desHis 1 Pro 4 Glu 9 (Lys 12 PAL)-glucagon-treated mice. These studies highlight the potential of glucagon receptor inhibition alone, and in combination with GIP receptor activation, for T2DM treatment.

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