Structure of the light chain-binding domain of myosin V

Boston Biomedical Research Institute, 64 Grove Street, Watertown, MA 02472, USA.
Proceedings of the National Academy of Sciences (Impact Factor: 9.67). 10/2005; 102(36):12718-23. DOI: 10.1073/pnas.0503899102
Source: PubMed


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 approximately 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-A 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.

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Available from: Grzegorz Rebowski
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    • "Instead of the conventional glycine, a residue with a large side-chain (M826) is found and the last arginine of the motif is replaced by a lysine (K830). Modelling studies proposed that this motif could recruit CaM by interaction with the C-lobe only, leaving the N-lobe free in solution (Terrak et al., 2005). However, the structure of the FLA shows that the N-lobe of CaM does interact with the HC helix and its position relative to the HC is analogous to that found for classic IQ motif/CaM complexes. "
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    • "In summary, we have identified two proteins, Ypt32p and Mlc1p, that are able to interact with the VBR of Myo2p opening up the possibility of defining how the interaction of the Myo2p GTD with organelle-linked receptors and Ypt32p-associated carriers is regulated. The high functional and structural conservation among phylogenetically distant myosin V of the patches of residues identified here as important for Ypt32p and Mlc1p binding (Pashkova et al., 2006; Weisman, 2006), the known ability of the Ypt32p-related Rab11 protein to interact with Myosin V GTD (Hales et al., 2002; Fielding et al., 2005) as well as the high conservation of essential light chains in structure and function throughout the evolution (Bahler and Rhoads, 2002; Terrak et al., 2005) strongly suggest that the interactions identified here are reciprocated in mammalian cells. "
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    • "It is also possible that CaBP1 competes for IQ binding with a single, loosely-bound lobe of calmodulin. Single-lobe light-chain binding has been proposed for Mlc1p binding to the IQ motifs of myosin-V (Terrak et al. 2005). "
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