Two single-headed myosin V motors bound to a tetrameric adapter protein form a processive complex

Abstract

The yeast class V myosin Myo4p moves processively in vivo in a cargo-dependent manner following formation of a double-headed complex with the adapter protein She3p and the mRNA-binding protein She2p.

Abstract

Myo4p, one of two class V myosins in budding yeast, continuously transports messenger RNA (mRNA) cargo in the cell but is nonprocessive when characterized in vitro. The adapter protein She3p tightly binds to the Myo4p rod, forming a single-headed motor complex. In this paper, we show that two Myo4p–She3p motors are recruited by the tetrameric mRNA-binding protein She2p to form a processive double-headed complex. The binding site for She3p was mapped to a single α helix that protrudes at right angles from She2p. Processive runs of several micrometers on yeast actin–tropomyosin filaments were observed only in the presence of She2p, and, thus, motor activity is regulated by cargo binding. While moving processively, each head steps ∼72 nm in a hand-over-hand motion. Coupling two high-duty cycle monomeric motors via a common cargo-binding adapter protein creates a complex with transport properties comparable with a single dimeric processive motor such as vertebrate myosin Va.