Mixed monolayers of two polypeptides at the water/air interface

Abstract

Mixed monolayers of two polypeptides, poly-γ-glutamate (PγMG) and poly-L-alanine (PLA), in the same α-helix surface comformations were studied at the water-air interface.

Their interphasal arrangement and their α-helix conformation were deduced by determining the spreading π-A isotherms and comparing them with Huggins’ theory, by infrared spectra obtained with multiple internal reflection (MIR) of the two polypeptides, and by ellipsometrical measurements carried out on transferred monolayers.

The study of mixed monolayers allows the deduction that the two polypeptides are completely miscible at the water-air interphase, and that they both keep their α-helix conformation in mixtures.

The hydrophobic nature of the attractive interactions in the PLA and PγMG mixtures was demonstrated by applying Joos’ theory to the collapse pressures determined at equilibrium conditions.

The collapse of the two polypeptides under equilibrium conditions was also studied using the scanning electron microscope.

The kinetic study of the collapse mechanism, both of the two separate components and for their mixtures, allows conclusions that the process consists essentially in nucleation and growth of a tridimensional phase and that in the collapsed phase, the two polypeptides are also compatible.