CONTROL OF AMP-DEAMINASE-1 BINDING TO MYOSIN HEAVY-CHAIN

AMP deaminase (AMPD) plays a central role in preserving the adenylate energy charge in myocytes following exercise and in producing intermed iates for the citric acid cycle in muscle. Prior studies have demonstr ated that AMPD1 binds to myosin heavy chain (MHC) in vitro; binding to the myofibril varies with the state of muscle contraction in vivo, an d binding of AMPD1 to MHC is required for activation of this enzyme in myocytes. The present study has identified three domains in AMPD1 tha t influence binding of this enzyme to MHC using a cotransfection model that permits assessment of mutations introduced into the AMPD1 peptid e. One domain that encompasses residues 178-333 of this 727-amino acid peptide is essential for binding of AMPD1 to MHC. This region of AMPD 1 shares sequence similarity with several regions of titin, another MH C binding protein. Two additional domains regulate binding of this pep tide to MHC in response to intracellular and extracellular signals. A nucleotide binding site, which is located at residues 660-674, control s binding of AMPD1 to MHC in response to changes in intracellular ATP concentration. Deletion analyses demonstrate that the aminoterminal 65 residues of AMPD 1 play a critical role in modulating the sensitivity to ATP-induced inhibition of MHC binding. Alternative splicing of the AMPD 1 gene product, which alters the sequence of residues 8-12, prod uces two AMPD 1 isoforms that exhibit different MHC binding properties in the presence of ATP. These findings are discussed in the context o f the various roles proposed for AMPD in energy production in the myoc yte.