Chemomechanical transduction in the actomyosin molecular motor by 2',3'-dideoxydidehydro-ATP and characterization of its interaction with myosin subfragment 1 in the presence and absence of actin.

The effect of torsional freedom about the N-glycoside bond of ATP in the ability of the nucleoside triphosphate to support chemomechanical transduction (Takenaka et al., 1978) has been investigated by examining the ability of the nucleotide analogue 2',3'-dideoxy-2',3'-didehydro-ATP (1b, enf-ATP) to act as a substrate for myosin subfragment 1 in the presence and absence of actin and to support actin sliding in the standard in vitro motility assay. By converting the ribosyl ring of the natural substrate to the rigid and almost planar enofuranosyl ring, effects on torsional freedom about the N-glycoside bond due to changes in ribosyl ring pucker and/or by steric interferences of the protons attached to the 2' and 3' carbons are eliminated allowing for increased torsional freedom about the N-glycoside bond. The data indicate that this enofuranosyl analogue is an excellent substrate for subfragment 1 and actosubfragment 1 and produces actin sliding velocities which are twice as fast as those observed with ATP in the standard in vitro motility assay. The analogue diphosphate is trapped in S1 by the common P(i) analogues, but the rate of formation of the ternary complex formed with Vi is very slow compared to that observed with MgADP. Similar conformations of S1 are formed with Mg.enf-ATP and MgATP under steady-state conditions, but S1 with bound Mg.enf-ADP differs significantly from that observed with MgADP.