Structure of the light chain-binding domain of myosin V

Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472

Edited by James A. Spudich, Stanford University School of Medicine, Stanford, CA, and approved July 28, 2005 (received for review May 10, 2005)

Abstract

Myosin V is a double-headed molecular motor involved in organelle transport. Two distinctive features of this motor, processivity and the ability to take extended linear steps of ≈36 nm along the actin helical track, depend on its unusually long light chain-binding domain (LCBD). The LCBD of myosin V consists of six tandem IQ motifs, which constitute the binding sites for calmodulin (CaM) and CaM-like light chains. Here, we report the 2-Å resolution crystal structure of myosin light chain 1 (Mlc1p) bound to the IQ2–IQ3 fragment of Myo2p, a myosin V from Saccharomyces cerevisiae. This structure, combined with FRET distance measurements between probes in various CaM–IQ complexes, comparative sequence analysis, and the previously determined structures of Mlc1p-IQ2 and Mlc1p-IQ4, allowed building a model of the LCBD of myosin V. The IQs of myosin V are distributed into three pairs. There appear to be specific cooperative interactions between light chains within each IQ pair, but little or no interaction between pairs, providing flexibility at their junctions. The second and third IQ pairs each present a light chain, whether CaM or a CaM-related molecule, bound in a noncanonical extended conformation in which the N-lobe does not interact with the IQ motif. The resulting free N-lobes may engage in protein–protein interactions. The extended conformation is characteristic of the single IQ of myosin VI and is common throughout the myosin superfamily. The model points to a prominent role of the LCBD in the function, regulation, and molecular interactions of myosin V.

Footnotes

↵ † To whom correspondence should be addressed. E-mail: dominguez{at}bbri.org.
↵ * M.T. and G.R. contributed equally to this work.
Author contributions: Z.G. and R.D. designed research; M.T., G.R., and R.D. performed research; R.C.L. contributed new reagents/analytic tools; M.T., G.R., Z.G., and R.D. analyzed data; and R.D. wrote the paper.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations: CaM, calmodulin; LCBD, light chain-binding domain; Mlc1p, myosin light chain 1; 1,5-IAEDANS, N-iodoacetyl-N′-(5-sulfo-1-naphthyl)ethylenediamine; DABMI, 4-dimethylaminophenylazophenyl-4′-maleimide.
Data deposition: The atomic coordinates have been deposited in the Protein Data Bank, www.pdb.org (PDB ID code 1N2D).