Dynamics of Fusarium solani cutinase investigated through structural comparison among different crystal forms of its variants.

In characterizing mutants and covalently inhibited complexes of Fusarium solani cutinase, which is a 197-residue lipolytic enzyme, 34 variant structures, crystallizing in 8 different crystal forms, have been determined, mostly at high resolution. Taking advantage of this considerable body of information, a structural comparative analysis was carried out to investigate the dynamics of cutinase. Surface loops were identified as the major flexible protein regions, particularly those forming the active-site groove, whereas the elements constituting the protein scaffold were found to retain the same conformation in all the cutinase variants studied. Flexibility turned out to be correlated with thermal motion. With a given crystal packing environment, a high flexibility turned out to be correlated with a low involvement in crystal packing contacts. The high degree of crystal polymorphism, which allowed different conformations with similar energy to be detected, made it possible to identify motions which would have remained unidentified if only a single crystal form had been available. Fairly good agreement was found to exist between the data obtained from the structural comparison and those from a molecular dynamics (MD) simulation carried out on the native enzyme. The crystallographic approach used in this study turned out to be a suitable tool for investigating cutinase dynamics. Because of the availability of a set of closely related proteins in different crystal environments, the intrinsic drawback of a crystallographic approach was bypassed. By combining several static pictures, the dynamics of the protein could be monitored much more realistically than what can be achieved on the basis of static pictures alone.