Ca2+/calmodulin regulation of the Arabidopsis kinesin-like calmodulin-binding protein.
The kinesin family motor protein KCBP (kinesin-like calmodulin binding protein) was identified during a screen for Arabidopsis calmodulin-binding proteins [Reddy, et al., 1996b: J. Biol Chem. 271:7052-7060]. KCBP contains a C-terminal motor domain and is unique among kinesin motors in that it has a calmodulin-binding site. We expressed the KCBP motor domain in Escherichia coli and examined its microtubule (MT) binding and ATPase activity. KCBP bound MTs in an ATP-dependent manner and exhibited MT-stimulated ATPase activity. Ca2+/ calmodulin inhibited binding of KCBP to MTs under conditions that normally favor tight motor-MT interactions, and the extent of inhibition was dependent on the concentration of calcium and calmodulin. Ca2+/calmodulin did not affect KCBP's basal ATPase activity, but reduced the motor's MT-stimulated ATPase activity. The substantial reduction in affinity of KCBP for MTs in the presence of Ca2+/calmodulin suggests that Ca2+/calmodulin may modulate the activity of KCBP in vivo by regulating the motor's association with MTs. KCBP is the first MT-dependent motor protein found to be regulated by direct binding of Ca2+/calmodulin to its motor subunit.
Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg 24061-0406, USA.
B E
BE
Deavours
A S
AS
Reddy
R A
RA
Walker
D000251:Adenosine Triphosphatases / Q000378:metabolism; D017360:Arabidopsis; D029681:Arabidopsis Proteins; D002118:Calcium / Q000378:metabolism*; D002147:Calmodulin / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism*; D011485:Protein Binding
D029681:Arabidopsis Proteins; D002147:Calmodulin; D002148:Calmodulin-Binding Proteins; C099551:KCBP protein, Arabidopsis; D010940:Plant Proteins; D000251:Adenosine Triphosphatases; D002118:Calcium