BUILDING PROTEIN BACKBONES FROM C-ALPHA COORDINATES

An automatic procedure for building polyalanine backbones from guiding alpha-carbon positions is presented. Polyalanine backbones are built based on the geometric restraints of angle N - C-alpha - C and the kno wledge of main-chain dihedral angle distributions. A building module c onstructs a list of polyalanine backbones that follow exactly the C-al pha trace. Then a selection module selects one backbone with the large st portion of phi-psi pairs in favoured regions. Several test cases on C-alpha coordinates from X-ray refined structures give acceptable res ults. Less than 10% of the peptide planes are incorrectly built, and t he result is not sensitive to random shift up to 0.5 angstrom of C-alp ha coordinates.