A POINT MUTATION WITHIN THE ATP-BINDING SITE INACTIVATES BOTH CATALYTIC FUNCTIONS OF THE ATP-DEPENDENT PROTEASE LA (LON) FROM ESCHERICHIA-COLI

A point mutant in the ATP-binding motif(GPPGVGK(362)T) of the ATP-dependent protease La from Escherichia coli was investigated in which the lysine at position 362 was replaced by an alanine. The catalytic efficiency of the K362A mutant is at least two orders of magnitude lower than that of wild-type protease La due to a decreased V-max and an increased K-M for ATP. Simultaneously, the peptidase activity of La K362A is almost completely eliminated. Since selective inactivation of the peptidase activity of La does not affect its intrinsic ATPase activity, coupling of proteolysis with ATP hydrolysis is only uni-directional in this energy-dependent protease.