ANISOTROPIC VIBRATIONAL ANALYSIS OF THE SMALL PROTEIN CRAMBIN. Martha M. Teeter* and Boguslaw Stec. Department of Chemistry, Boston College, Chestnut Hill, MA 02167. *Sabbatical address: Max Planck Institute for Biophysics, 60528 Frankfurt/Main, Germany.

Full Matrix Least Squares refinement of the small protein crambin (4.7 kDa, 46 residues) at 0.83 resolution and 130K permits full anisotropic refinement of most atoms in the protein (Stec, Zhou and Teeter, (1995) Acta Cryst. D51, 663-681). With the program RFINE, the protein can be refined by the small molecule vibrational method of TLS refinement (Schomaker, V. and Trueblood, K. (1968) Acta Cryst. B24, 63-76). This refinement can show how well the atomic displacement for the protein atoms are modeled by rigid body movement. It can also indicate non-rigid body motion, such as disorder, and aid in determination of external or lattice contributions to the anisotropic vibration factors.

Better agreement with individual B value refinement is found with three-rigid bodies rather than with two or one. However, the deviations in single rigid body B values from the individual B values are found to occur at disordered residues. This means that such a plot can be useful to indicate disorder, modeled or unmodeled.

We have used TLS to estimate the percentage of the B values that is due to external vibration. In this approach, we modeled the protein as one rigid body, two rigid bodies and three rigid body. We hypothesized that the common parts of the tensors for these three descriptions would represent the external or lattice contribution to the vibrational factors. This leads to the conclusion that 60% of the motion is external. This is in agreement with Diamond's refinement of a protein using by normal modes (Diamond, R. (1990) Acta Cryst. A46, 425-435), where external vibration was found to dominate the B value.