Probing peptide-mediated membrane pore formation by fluorescence, infrared spectroscopy, and atomic force microscopy

Abstract

Membrane pores and channels play key roles in cell physiology. Hence, the elucidation of their structure is important for understanding their molecular mechanisms and for designing drugs to recover their impaired function during various pathologies. Atomic resolution structural techniques such as X-ray crystallography or nuclear magnetic resonance have made strides in studying membrane proteins but still encounter difficulties due to resistance to crystallization and the large size of protein-membrane complexes. Other biophysical methods are being employed to tackle these proteins. The focus of this article is on three such approaches, i.e., fluorescence, Fourier transform infrared spectroscopy, and atomic force microscopy. The application of these techniques to characterize ion conducting pore formation by various peptides in lipid bilayers is described. Combined, these approaches provide comprehensive information on pore structure and function such as the kinetics of pore assembly, pore size, stoichiometry, peptide-peptide affinities, the secondary structure, depth of membrane insertion, the orientation of the pore-forming peptide molecules with respect to the membrane, and the supramolecular morphology of the membrane-embedded functional pore.