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Curr Biol. 2012 Aug 7;22(15):1410-6. doi: 10.1016/j.cub.2012.05.035. Epub 2012 Jun 14.

Tropomyosin is essential for processive movement of a class V myosin from budding yeast.

Author information

1
Department of Molecular Physiology and Biophysics, University of Vermont, Burlington, VT 05405, USA.

Abstract

Myosin V is an actin-based motor protein involved in intracellular cargo transport [1]. Given this physiological role, it was widely assumed that all class V myosins are processive, able to take multiple steps along actin filaments without dissociating. This notion was challenged when several class V myosins were characterized as nonprocessive in vitro, including Myo2p, the essential class V myosin from S. cerevisiae [2-6]. Myo2p moves cargo including secretory vesicles and other organelles for several microns along actin cables in vivo. This demonstrated cargo transporter must therefore either operate in small ensembles or behave processively in the cellular context. Here we show that Myo2p moves processively in vitro as a single motor when it walks on an actin track that more closely resembles the actin cables found in vivo. The key to processivity is tropomyosin: Myo2p is not processive on bare actin but highly processive on actin-tropomyosin. The major yeast tropomyosin isoform, Tpm1p, supports the most robust processivity. Tropomyosin slows the rate of MgADP release, thus increasing the time the motor spends strongly attached to actin. This is the first example of tropomyosin switching a motor from nonprocessive to processive motion on actin.

PMID:
22704989
PMCID:
PMC3570268
DOI:
10.1016/j.cub.2012.05.035
[Indexed for MEDLINE]
Free PMC Article

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