研究人员对普遍存在的运动蛋白kinesin已经进行了广泛研究，但一个基本的机制问题仍然没有得到回答：当kinesin在每8纳米的步长之间等待时它是两头都与微管结合在一起的还是只有一头与微管结合？现在，Mori等人研制出单分子荧光共振能量转移传感器（smFRET），用来在该运动蛋白沿微管运动时对其进行跟踪。他们发现，在生理浓度的ATP中，kinesin是以一种双头结合状态在两个步长之间等待的，而在低浓度的ATP中，它主要以单头结合状态出现。
原始出处:
Nature 450, 750-754 (29 November 2007) | doi:10.1038/nature06346; Received 18 April 2007; Accepted 2 October 2007; Published online 14 November 2007
How kinesin waits between steps
Teppei Mori1, Ronald D. Vale2 & Michio Tomishige1,2
Department of Applied Physics, The University of Tokyo, Tokyo 113-8656, Japan
Howard Hughes Medical Institute and Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94158, USA
Correspondence to: Ronald D. Vale2 Correspondence and requests for materials should be addressed to R.D.V. (Email: vale@cmp.ucsf.edu).
Kinesin-1 (conventional kinesin) is a dimeric motor protein that carries cellular cargoes along microtubules1, 2 by hydrolysing ATP3 and moving processively in 8-nm steps4. The mechanism of processive motility involves the hand-over-hand motion of the two motor domains ('heads')5, 6, 7, a process driven by a conformational change in the neck-linker domain of kinesin8, 9, 10, 11, 12. However, the 'waiting conformation' of kinesin between steps remains controversial13, 14, 15, 16—some models propose that kinesin adopts a one-head-bound intermediate17, 18, 19, 20, 21, whereas others suggest that both the kinesin heads are bound to adjacent tubulin subunits7, 22, 23. Addressing this question has proved challenging, in part because of a lack of tools to measure structural states of the kinesin dimer as it moves along a microtubule. Here we develop two different single-molecule fluorescence resonance energy transfer (smFRET) sensors to detect whether kinesin is bound to its microtubule track by one or two heads. Our FRET results indicate that, while moving in the presence of saturating ATP, kinesin spends most of its time bound to the microtubule with both heads. However, when nucleotide binding becomes rate-limiting at low ATP concentrations, kinesin waits for ATP in a one-head-bound state and makes brief transitions to a two-head-bound intermediate as it walks along the microtubule. On the basis of these results, we suggest a model for how transitions in the ATPase cycle position the two kinesin heads and drive their hand-over-hand motion.
