Using infrared spectroscopy of a nitrile labeled phenylalanine and tryptophan fluorescence to probe the α-MSH peptide’s side-chain interactions with a micelle model membrane

•Trp fluorescence suggests that the Trp9 side-chain is buried in an SDS micelle.•IR spectroscopy of Phe(CN)7 suggests that the Phe(CN)7 side-chain is not buried in SDS.•Phe(CN)7 and Trp9 side-chains are not similarly interacting with an SDS micelle.•IR data of a nitrile label complemented Trp fluorescence data quite well.

The interactions of α-MSH (Ac-SYSMEHFRWGKPV-NH2) side-chains were biophysically characterized with a micelle model membrane and in model intracellular bacterial conditions using infrared (IR) spectroscopy of a nitrile labeled α-MSH analogue, circular dichroism (CD), and tryptophan fluorescence. Local changes detected by the tryptophan and a nitrile-labeled phenylalanine using fluorescence and infrared spectroscopies, respectively, suggest that the Trp9 side-chain in the conserved core (HisPheArgTrp) of α-MSH is buried in an SDS micellar environment, while Phe(CN)7 does not appear to be buried.

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