Optimal description of a protein structure in terms of multiple groups undergoing TLS motion.

A single protein crystal structure contains information about dynamic properties of the protein as well as providing a static view of one three-dimensional conformation. This additional information is to be found in the distribution of observed electron density about the mean position of each atom. It is general practice to account for this by refining a separate atomic displacement parameter (ADP) for each atomic center. However, these same displacements are often described well by simpler models based on TLS (translation/libration/screw) rigid-body motion of large groups of atoms, for example interdomain hinge motion. A procedure, TLSMD, has been developed that analyzes the distribution of ADPs in a previously refined protein crystal structure in order to generate optimal multi-group TLS descriptions of the constituent protein chains. TLSMD is applicable to crystal structures at any resolution. The models generated by TLSMD analysis can significantly improve the standard crystallographic residuals R and R(free) and can reveal intrinsic dynamic properties of the protein.