N.m.r. study of conformational changes in lysozyme around the thermal transition point

Natural abundance carbon-13 n.m.r. at 50.3 MHz has been used to further document the thermal transition that hen egg-white lysozyme undergoes in solution between 20 degrees and 30 degrees. The study focuses on the temperature sensitivity of more than 50 carboxylic, aromatic and aliphatic single carbon resonances for which unambiguous assignments to specific residues are known. The analysis of selective perturbations in chemical shifts indicates that residues located on both edges of the active site cleft and in the hydrophobic box are primarily involved in the temperature-induced conformational transition. N.m.r. results are compared with crystallographic data on low temperature (form A) and high temperature (form B) interconverting lysozyme crystals, taking advantage of the recent availability of quality high resolution maps for B form orthorhombic crystals. In most cases, a good correlation is found at the atomic level between residues involved in the thermal transition in solution and in the crystalline state. Discrete discrepancies are noted for some residues such as Trp-62 and His-15.