Folded proteins, molecular dimension

Using the precision of gene template directed biosymthesis, they have produced chain folded lamellae of exact molecular dimensions. These molecular films may be used to position functional groups in precise locations on tlie lamellar planes. Tirrell et al. (1991) have also demonstrated that under special circumstances certain unnatural amino acids with chemically interesting side chains can be incorporated into protein polymer chains. This further increases the potential diversity of compositions and properties that may be obtained through protein polymers. 

The structure of any molecule is a unique and specific aspect of its identity. Molecular structure reaches its pinnacle in the intricate complexity of biological macromolecules, particularly the proteins. Although proteins are linear sequences of covalently linked amino acids, the course of the protein chain can turn, fold, and coil in the three dimensions of space to establish a specific, highly ordered architecture that is an identifying characteristic of the given protein molecule (Figure 1.11). 

The MoFe proteins from Clostridiumpasteurianum and from Azotobacter vinelandii have been crystallized. For the former protein, crystals of space group P2i are obtained, with two molecules per unit cell of dimensions 70 X 151 X 122 A. There is good evidence for a molecular two-fold axis, which presumably relates equivalent sites in the two a/3 dimers that make up the protein molecule.Preliminary refinement reveals that the two FeMoco units per protein are about 70 A apart and the four P clusters are grouped in two pairs. 

The evolution of cytochrome c and protein molecules in general has been the subject of many papers and reviews, and can be treated relatively briefly here. The starting points must be Anfinson s Molecular Basis of Evolution (57), based on the early amino acid sequence work, and the discovery that same year by Kendrew and Perutz of the identity of three-dimensional folding of the related proteins myoglobin and hemoglobin (98,99). These illustrate the two components of any study of mac-romolecular evolution the chemical sequence of the polymer and the folding of the polymer in three dimensions. 

The actual dimensions of the molecule depend on the extent of chain folding and regulate many of its physicochemical properties. This, not the actual molecular mass, is the parameter commonly measured for cosmetic proteins and related to their properties and benefits. 

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