Loop closure in proteins requires computing the values of the inverse kinematics (IK) map for a backbone fragment with 2n 6 torsional degrees of freedom (dofs). It occurs in a variety of contexts, e.g., structure determination from electron-density maps, loop insertion in homology-based structure prediction, backbone tweaking for protein energy minimization, and study of protein mobility in folded states. The first part of this paper analyzes the global structure of the IK map for a fragment of protein backbone with 6 torsional dofs and a slightly idealized kinematic model, called the canonical model. This model, which assumes that every two consecutive torsional bonds C
R. James Milgram, Guanfeng Liu, Jean-Claude Latomb