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© The Rockefeller University Press, 0021-9525/1998//1053 $5.00
The Journal of Cell Biology, Volume 143, Number 4, , 1998 1053-1066

Regular Articles

Light Chain– dependent Regulation of Kinesin's Interaction with Microtubules



Kristen J. Verhey{ddagger}, Donna L. Lizotte*, Tatiana Abramson*, Linda Barenboim{ddagger}, Bruce J. Schnapp*, and Tom A. Rapoport{ddagger}

* Department of Cell Biology and {ddagger} Howard Hughes Medical Institute, Harvard Medical School, Boston, Massachusetts 02115

We have investigated the mechanism by which conventional kinesin is prevented from binding to microtubules (MTs) when not transporting cargo. Kinesin heavy chain (HC) was expressed in COS cells either alone or with kinesin light chain (LC). Immunofluorescence microscopy and MT cosedimentation experiments demonstrate that the binding of HC to MTs is inhibited by coexpression of LC. Association between the chains involves the LC NH2-terminal domain, including the heptad repeats, and requires a region of HC that includes the conserved region of the stalk domain and the NH2 terminus of the tail domain. Inhibition of MT binding requires in addition the COOH-terminal 64 amino acids of HC. Interaction between the tail and the motor domains of HC is supported by sedimentation experiments that indicate that kinesin is in a folded conformation. A pH shift from 7.2 to 6.8 releases inhibition of kinesin without changing its sedimentation behavior. Endogenous kinesin in COS cells also shows pH-sensitive inhibition of MT binding. Taken together, our results provide evidence that a function of LC is to keep kinesin in an inactive ground state by inducing an interaction between the tail and motor domains of HC; activation for cargo transport may be triggered by a small conformational change that releases the inhibition of the motor domain for MT binding.

Key Words: kinesin • microtubules • molecular motors

Abbreviations used in this paper: HA, hemagglutinin; HC, heavy chain; LB, Lysis buffer; LC, light chain; MT, microtubule; ORF, open reading frame; TPR, tetratricopeptide repeat.

K.J. Verhey was supported by a National Institutes of Health (NIH) postdoctoral fellowship. T.A. Rapoport is a Howard Hughes Medical Institute investigator. This work was supported in part by NIH grants to B.J. Schnapp.

Address all correspondence to Bruce J. Schnapp, Department of Cell Biology, Harvard Medical School, 240 Longwood Ave., Boston, MA 02115. Tel.: (617) 432-3818. Fax: (617) 432-1144. E-mail: schnapp{at}warren.med.harvard.edu


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