The structure of phage T4 lysozyme in solution noticeably differs from its crystalline structure

In the preceding paper [l] it was shown by the method of large-angle diffuse X-ray scattering [2,3] that the structure of bovine pancreatic ribonuclease and that of its complex with an inhibitor in solution coincide with their crystalline structures(on a distance scale 2 10 A). Also it was shown [2] that hen egg white lysozyme structure in solution differs from its crystalline structure by a small opening of the substrate-binding cleft, the binding of the competitive inhibitor stabilizing the closed state of the cleft observed in the crystalline structure. Sperm whale myoglobin structure in solution also differs from its crystalline structure, the differences being interpreted as changes of the GH hairpin position relative to the remaining part of the molecule [4] . In all probability in both cases we are dealing with fluctuations in relative positions of large masses of a protein molecule which are frozen in the crystalline structure but which manifest themselves in solution. The possibility of such fluctuations was demonstrated by direct model calculations for hen egg-white lysozyme [2]. Here the above-mentioned method has been used to study phage T4 lysozyme. The crystalline structure of this protein is characterized by the closed substratebinding cleft, therefore ‘in order to allow the substrate to enter, the enzyme would have to undergo a fairly substantial conformational change’ [6] . Our results provide evidence of a noticeable difference between