Leucine Fastener Formation Mechanism between Peptide β-Sheets in a Monolayer Studied by Infrared Multiple-Angle Incidence Resolution Spectroscopy

A leucine zipper and a leucine fastener formed between peptide molecules have been hypothetical models of a molecular association via interdigitation. As a molecular interaction mechanism, a “leucine zipper” with the aid of an α-helix backbone in biological peptides is believed to play an important role in the molecular association, but no experimental evidence to prove the zipping has been reported thus far. In the same fashion, a “leucine fastener” built on the structure of peptide β-sheets has never been experimentally captured either. In the present study, very fine changes of molecular stress and orientation in monolayers of a synthesized tetraleucine-containing amphiphile before and after the molecular interdigitation have readily been detected by infrared multiple-angle incidence resolution spectroscopy, which was recently developed for the analysis of structural anisotropy in thin materials. It has been suggested that the conventional molecular orientation model of the leucine fastener should be modified, and the backbone structure (parallel β-sheet in the present study) plays a necessary role for the interlock of the leucine fastener.