ADPbound

ADPbound is a descriptive term used in biochemistry and structural biology to denote a protein or enzyme in which an adenosine diphosphate molecule is bound at a nucleotide-binding site, typically after hydrolysis of ATP. Across many families of nucleotide-binding proteins, function cycles through ATP-bound, ADP-bound, and nucleotide-free states, with the ADP-bound state often corresponding to a post-hydrolysis conformation that influences activity and interactions. The ADP-bound conformation can alter the geometry of the catalytic pocket, modulate affinity for substrates or regulatory partners, and bias the protein toward specific structural states.

In structural studies, ADP-bound forms are commonly observed in X-ray crystallography, cryo-electron microscopy, and NMR analyses captured by soaking or co-crystallization with ADP or ADP analogs. Biochemical assays measuring nucleotide exchange rates and hydrolysis kinetics are used to characterize ADPbound behavior. The term is widely applied to motor proteins, chaperones, and many enzymes that rely on nucleotide binding to drive conformational cycles.

Applications include understanding mechanism, informing drug design that stabilizes the ADP-bound state, and interpreting disease-related mutations that affect nucleotide handling. The use of the term can vary among protein families, and structural context is important, as some proteins exchange nucleotides rapidly or sample multiple bound states in solution rather than adopting a single ADP-bound conformation.

See also nucleotide-binding domain, ATPase, and GTPase.