FULL-MATRIX LEAST-SQUARES REFINEMENT OF LYSOZYMES AND ANALYSIS OF ANISOTROPIC THERMAL MOTION

Crystal structures of turkey egg lysozyme (TEL) and human lysozyme (HL ) were refined by full-matrix least-squares method using anisotropic t emperature factors, The refinement converged at the conventional R-val ues of 0.104 (TEL) and 0.115 (HL) for reflections with F-o > 0 to the resolution of 1.12 Angstrom and 1.15 Angstrom, respectively, The estim ated r.m.s. coordinate errors for protein atoms were 0.031 Angstrom (T EL) and 0.034 Angstrom (HL). The introduction of anisotropic temperatu re factors markedly reduced the R-value but did not significantly affe ct the main chain coordinates. The degree of anisotropy of atomic ther mal motion has strong positive correlation with the square of distance from the molecular centroid. The ratio of the radial component of the rmal ellipsoid to the r.m.s. magnitude of three principal components h as negative correlation with the distance from the molecular centroid, suggesting the domination of libration rather than breathing motion. The TLS model was applied to elucidate the characteristics of the rigi d-body motion. The TLS tensors were determined by the least-squares fi t to observed temperature factors. The profile of the magnitude of rep roduced temperature factors by the TLS method well fitted to that of o bserved B-eqv. However, considerable disagreement was observed in the shape and orientation of thermal ellipsoid for atoms with large temper ature factors, indicating the large contribution of local motion, The upper estimate of the external motion, 67% (TEL) and 61% (HL) of B-eqv , was deduced from the plot of the magnitude of TLS tensors determined for main chain atoms which were grouped into shells according to the distance from the center of libration. In the external motion, the tra nslational portion is predominant and the contribution of libration an d screw motion is relatively small, The internal motion, estimated by subtracting the upper estimate of the external motion from the observe d temperature factor, is very similar between TEL and HL in spite of t he difference in 54 of 130 amino acid residues and in crystal packing, being suggested to reflect the intrinsic internal motion of chicken-t ype lysozymes. (C) 1998 Wiley-Liss, Inc.