X-ray structural analysis of compensating mutations at the barnase-barstarinterface

The crystal structure of the barstar mutants (Y29P) and (Y29D, Y30W) as wel l as that of the complexes of barstar(Y29P) with mild-type barnase and barn ase(H102K) have been determined, These barstar mutants compensate for the d ramatic loss of barnase-barstar interaction energy caused by a single mutat ion of the barnase active site His-102 to a lysine. The latter introduces a n uncompensated charge in the pocket at the surface of barstar where Lys-10 2 is located. The analysis of the structures suggests a mechanism for this compensation based on the solvation of the charge of Lys-102. Additional co mpensation occurs through the formation of a hydrogen bond. (C) 1999 Federa tion of European Biochemical Societies.