Polypeptide block copolymer membranes

In biological membranes, integral proteins are amphipatic molecules their hydro-phobic moiety is embedded in the lipid bilayer and their hydrophilic moiety protrudes from the surface of the membrane279. So, it was interesting to prepare polymeric models of such amphipatic proteins. For that purpose, two new classes of block copolymers have been synthetized in Orleans, namely copolymers with a polyvinyl block and a polypeptide block and copolymers with a saccharide and a peptide block. We shall give some information concerning the preparation of these copolymers and then describe their structure. 

Linear polypeptide block copolymers, block copolymers with pendent sugar or peptide grafts, and modified linear or dendritic homopolymers have been used to produce vesicles based on hydrophobic interactions and packing issues. Usually, the peptides or sugars make the minority hydrophilic part of the copolymers and are thus incorporated in the corona and not in the membrane of the vesicles. For the inverse case, the hydrophobic peptides in the membrane are often too short to adopt a stable secondary structure. 

Block copolymers containing a biologically active, polypeptide block were originally studied as models for biological membranes. The variety of conformations of polypeptides (a-helix, )3-sheet, and random coil) were expected to produee new copolymers of technical interest [10]. 

We are now preparing and studying membrane models formed by ternary systems amphipatic block copolymer/lipids/water. From the interaction with our polymeric models of lectins (lectins are proteins or glycoproteins specific of different sugar residues] we hope to obtain informations about the respective parts played by the different carbohydrate chains and the polypeptide skeleton of glycoproteins and perhaps help to throw some light on problems as important as cell recognition and cell contact inhibition. 

STRUCTURE AND PROPERTIES OF POLYPEPTIDE BLOCK COPOLYMER MEMBRANES... 

The aim of this research was therefore to extend fundamental investigations on the preparation and molecular characterizations, structures, and functional properties of both of the bulk and the surface of A-B-A tri-block copolymer membranes in which A is a polypeptide and B is polybutadiene or polytetramethyleneoxide. 

Chain Conformation of Polypeptide Component in Block Copolymer Membranes... 

The behaviour of copolymers SK is typical for the behaviour of copolymers with a hydrophobic polyvinyl block and a hydrophilic polypeptide block. They exhibit mesophases in water for water concentration ranging from 0 to 50% and the structure of the mesophases is lamellar23. The special feature of this lamellar structure consists in the conformation of the polylysine chains which are roughly to 15% in a 0-chain conformation, to 35% in an a-helix conformation and to 50% in a coiled conformation23, so that the hydrophilic block of such amphipatic copolymers has the same type of conformation as the hydrophilic part of the membrane proteins. 

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