  The conformations available to polypeptides are determined by the interatomic
forces acting on the peptide units, whereby backbone torsion angles are
restricted as described by the Ramachandran plot. Although typical proteins are
composed predominantly from {\alpha}-helices and {\beta}-sheets, they
nevertheless adopt diverse tertiary structure, each folded as dictated by its
unique amino-acid sequence. Despite such uniqueness, however, the functioning
of many proteins involves changes between quite different conformations. The
study of large-scale conformational changes, particularly in large systems, is
facilitated by a coarse-grained representation such as provided by virtually
bonded C{\alpha} atoms. We have developed a virtual atom molecular mechanics
(VAMM) force field to describe conformational dynamics in proteins and a
VAMM-based algorithm for computing conformational transition pathways. Here we
describe the stereochemical analysis of proteins in this coarse-grained
representation, comparing the relevant plots in coarse-grained conformational
space to the corresponding Ramachandran plots, having contoured each at levels
determined statistically from residues in a large database. The distributions
shown for an all-{\alpha} protein, two all-{\beta} proteins and one
{\alpha}+{\beta} protein serve to relate the coarse-grained distributions to
the familiar Ramachandran plot.
