Deavours B E, Reddy A S, Walker R A
Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg 24061-0406, USA.
Cell Motil Cytoskeleton. 1998;40(4):408-16. doi: 10.1002/(SICI)1097-0169(1998)40:4<408::AID-CM8>3.0.CO;2-6.
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.
驱动蛋白家族的驱动蛋白KCBP（类驱动蛋白钙调蛋白结合蛋白）是在对拟南芥钙调蛋白结合蛋白的筛选过程中被鉴定出来的[雷迪等人，1996b：《生物化学杂志》271：7052 - 7060]。KCBP含有一个C端驱动结构域，在驱动蛋白中是独特的，因为它有一个钙调蛋白结合位点。我们在大肠杆菌中表达了KCBP驱动结构域，并检测了其与微管（MT）的结合及ATP酶活性。KCBP以ATP依赖的方式结合MT，并表现出MT刺激的ATP酶活性。在通常有利于紧密的驱动蛋白 - MT相互作用的条件下，Ca2+/钙调蛋白抑制KCBP与MT的结合，抑制程度取决于钙和钙调蛋白的浓度。Ca2+/钙调蛋白不影响KCBP的基础ATP酶活性，但降低了驱动蛋白的MT刺激的ATP酶活性。在存在Ca2+/钙调蛋白的情况下，KCBP对MT的亲和力大幅降低，这表明Ca2+/钙调蛋白可能通过调节驱动蛋白与MT的结合来在体内调节KCBP的活性。KCBP是第一个被发现通过Ca2+/钙调蛋白直接结合到其驱动亚基而受到调节的MT依赖性驱动蛋白。
