Polypeptide layers

Niwa M, Murata T, Kitamatsu M, Matsumoto T, Higashi N. Spontaneous formation of single- and double-layered polypeptide assemblies based upon a helix-macrodipole interaction. J Mater Chem 1999 9 343-344. 

The so-called globin proteins are an important group of a-helical proteins. These include hemoglobins and myoglobins from many species. The globin structure can be viewed as two layers of helices, with one of these layers perpendicular to the other and the polypeptide chain moving back and forth between the layers. 

The ionized forms of polypeptides exhibit many characteristics in common therefore, we have studied them under various conditions. The most interesting observation is the transition of a polyelectrolyte brush found by changing the polyelectrolyte chain density. The brush layers have been prepared by means of the LB film deposition of an amphiphile, 2C18PLGA(48), at pH 10. Mixed monolayers of 2C18PLGA(48) and dioctadecylphos-phoric acid, DOP, were used in order to vary the 2C18PLGA(48) content in the monolayer. 

Another property specific to /l-solenoids is the existence of a well-defined boundary between the interior side chains that form the hydrophobic core and the side chains at solvent-exposed surfaces. This boundary is formed by a tighdy packed layer of H-bonded polypeptide backbones wrapping around the hydrophobic core. 

Strand-turn-strand motifs in /1-solenoids differ fundamentally from those found in globular proteins. In globular structures, two adjacent strands with an intervening /l-turn form an antiparallel structure called a /1-hairpin (Fig. 10A). In /1-solenoids, the polypeptide chain also folds back on itself, but the flanking /1-strands make contact via their side chains rather than interacting via H-bonds of the backbone (Fig. 10A). As a result, consecutive strands find themselves in two different, parallel, /1-sheets. The latter strand-turn-strand structure is called a /1-arch, and its turn, a /1-arc (Hennetin et at., 2006 Yoder and Jurnak, 1995). In /1-solenoids, /1-arches stack in-register to form /1-arcades which have two parallel /1-sheets assembled from corresponding strands in successive layers. 

Pauling, L., and Corey, R. B. (1951). The pleated sheet, a new layer configuration of polypeptide chains. Proc. Natl. Acad. Sci. USA 37, 251-256. 

In both cases the top layer of these layered polyelectrolyte films contains many ion sites that can bind redox ions by ion exchange vdth the electrolyte solution. Homo polypeptides such as poly(L-lysine) and poly(L-glutamic add) have been employed to form layered polyelectrolyte films with Fe(CN)6 " electrostatically adsorbed onto ammonium sites in poly(lysine) [45]. Modified electrodes with polyelectrolytes mono-layers have also been deposited using the Langmuir-Blodgett technique [46-48]. 

Fig. 1. The structure of the LHCII monomer as derived from electron crystallography [51], A proposed topography of the polypeptide in the photosynthetic membrane. Letters A, B and C indicate the three hydrophobic ix-helices spanning the membrane. Chlorophyll molecules are arranged into two rings roughly parallel to the membrane plane. B Approximate position of the chlorophyll in the upper level (left) and lower level (right) on the membrane plane. Dashed lines outline a-helices A, B and C. Chlorophyll molecules are oriented perpendicular to the membrane plane and are thus represented as black bars. Chlorophylls numbered as 6,7 and 8 are closer to those belonging to the lower layer than the other pigment molecules...

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