Purification and characterization of two monomeric kinesin constructs.

Steady-state and pre-steady-state kinetic methods were used to analyze two shorter Drosophila kinesin constructs (K341 and K366) in comparison to K401. K341, K366, and K401 represent the kinesin motor domains containing the N-terminal 341, 366, or 401 amino acids, respectively. K401 is dimeric (Kd = 37 +/- 17 nM) whereas both K366 and K341 are monomeric [Correia et al. (1995) Biochemistry 34, 4898-4907]. Like native kinesin and K401, K341 and K366 demonstrate low ATPase activity in the absence of microtubules (0.03 and 0.01 s-1, respectively), and ADP release is rate-limiting during steady-state turnover. Microtubules activate the steady-state ATPase to 84 s-1 for K341 (K(m),ATP = 100 microM; K0.5,MT = 3.2 microM tubulin) and 64 s-1 for K366 (K(m),ATP = 65 microM; K0.5,MT = 2.5 microM tubulin) in comparison to K401 at 20 s-1 (K(m)ATP = 60 microM; K0.5,MT = 1 microM tubulin). The rapid quench experiments for all three constructs show a burst of product formation during the first turnover, indicating the rate-limiting step for the microtubule-activated ATPase occurs after ATP hydrolysis. The interaction of K341 and K366 with the microtubule was analyzed by electron microscopy. The results show that K341 and K366, like K401, bind to the microtubule with an 8 nm axial periodicity. However, the addition of K366 to microtubules resulted in significant aggregation of microtubules. The pre-steady-state kinetic results show that K341 retains the kinetic and structural properties necessary to compare directly the kinetic properties of monomeric and dimeric kinesins, although the microtubule-activated ATPase is significantly faster for the monomeric constructs, suggesting possible interactions in the dimer which inhibit ATP turnover as part of the coupling to force production.