The Binding Mode of an ADP Analogue to a Metallohydrolase Mimics the Likely Transition State

Abstract

Purple acid phosphatases (PAPs) are members of the large family of metallohydrolases, a group of enzymes that perform a wide range of biological functions, while employing a highly conserved catalytic mechanism. PAPs are found in plants, animals and fungi; in humans they play an important role in bone turnover and are thus of interest for developing treatments for osteoporosis. The majority of metallohydrolases use a metal‐bound hydroxide to initiate catalysis, which leads to the formation of a proposed five‐coordinate oxyphosphorane species in the transition state. In this work, we crystallized PAP from red kidney beans (rkbPAP) in the presence of both adenosine and vanadate. The in crystallo‐formed vanadate analogue of ADP provides detailed insight into the binding mode of a PAP substrate, captured in a structure that mimics the putative fivecoordinate transition state. Our observations not only provide unprecedented insight into the mechanism of metallohydrolases, but might also guide the structure‐based design of inhibitors for application in the treatment of several human illnesses.