Poster: Cytoskeleton: Structure & Function

Abs # 1107: A novel calcium-binding protein with one EF-hand motif regulates the microtubule binding and ATPase activity of the plant kinesin KCBP

Presenter:	Day, Irene S, iday@colostate.edu
Authors	Day, Irene S (A)   Thomas, Tyler  (A)   Reddy, Vaka S (A)   Reddy, Anireddy S. (A) (B)
Affiliations:	(A): Colorado State University, Department of Biology (B): Program in Cell and Molecular Biology

Kinesin-like calmodulin (CaM)-binding protein (KCBP) is a unique member of the kinesin superfamily. Besides the three typical kinesin domains it has two features that make it unique: a calmodulin binding domain (CBD) at the C-terminus and a myosin tail homology (MyTH4) and talin-like region at the N-terminus. CaM binding occurs within a 23-amino acid stretch C-terminal to the motor domain. The interaction of KCBP with microtubules (MTs) and the MT-dependent ATPase activity of KCBP are inhibited by CaM in a calcium-dependent manner. Earlier results indicate the involvement of KCBP in cell division and trichome morphogenesis. Using the motor domain (including 15 amino acids of the coiled-coil region and the calmodulin-binding domain), a yeast two-hybrid screen identified a novel calcium-binding protein with a single EF-hand motif (KIC, kinesin-interacting CCD-1-like protein). In vitro co-precipitation studies confirmed the interaction of KIC with KCBP and KIC was shown to bind calcium at a physiological concentration and interact specifically with the CaM-binding domain of KCBP in a calcium-dependent manner. Our studies show that in the presence of both calcium and KIC, the binding of KCBP to microtubules is abolished whereas calcium or KIC alone has no effect. The MT-dependent ATPase activity of KCBP is also abolished, suggesting that activated KIC regulates KCBP activity. The concentration of calcium required for KIC to abolish the MT-dependent ATPase activity of KCBP is less than that required for calmodulin. These results indicate that two distinct calcium-binding proteins regulate the activity of KCBP and that both are likely to play a role in regulating KCBP activity in vivo in response to signal-induced changes in cytosolic calcium.