Ca2/calmodulin regulation of the Arabidopsis kinesin‐like calmodulin‐binding protein

Abstract

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.

Arabidopsis KCBP interacts with AIR9 but stays in the cortical division zone throughout mitosis via its MyTH4-FERM domain

“…The interaction of Ca 2+ /calmodulin with KCBP interferes with microtubule binding of the motor domain (Deavours et al, 1998;Narasimhulu and Reddy, 1998), and Vos et al (Vos et al, 2000) used microinjection of Tradescantia stamen hair cells to activate KCBP throughout cell division using an antibody directed against its calmodulin-binding domain. This led to the conclusion that the motor activity of KCBP is normally downregulated during metaphase but is reactivated during anaphase when its minus end activity draws microtubules together at the spindle poles.…”

Trichome morphogenesis inArabidopsis

“…The ZWI gene was cloned by a T-DNA tagging approach and encodes a kinesin-related protein containing a calmodulin-binding domain (Oppenheimer et al 1997). In vitro, the ZWI protein binds to microtubules in a Ca 2+ /calmodulin-dependent manner suggesting that its activity or the spatial regulation of its activity is regulated by Ca 2+ / calmodulin also in vivo (Deavours et al 1998;Reddy et al 1996a,b). In synchronized Arabidopsis and tobacco cell cultures ZWI localizes to the preprophase band, the mitotic spindle and the phragmoplast (Bowser & Reddy 1997).…”

The IQD Family of Calmodulin-Binding Proteins Links Calcium Signaling to Microtubules, Membrane Subdomains, and the Nucleus

“…During cell division, KCBP localizes to the cortical division zone and likely functions in phragmoplast guidance and in the spatial control of cytokinesis (Buschmann et al, 2015). The activity of KCBP/ZWI is regulated by Ca 2+ -CaM (Kao et al, 2000), and CaM binding abolishes MT interaction of its motor domain (Deavours et al, 1998;Narasimhulu and Reddy, 1998). Because not all effects of CaM/CMLs on MT arrays may be explained by KCBP action, additional players likely are required for the CaM-dependent regulation of MT organization and dynamics (Hepler, 2016).…”