A binding protein regulates myosin-7a dimerization and actin bundle assembly

Abstract

Myosin-7a, despite being monomeric in isolation, plays roles in organizing actin-based cell protrusions such as filopodia, microvilli and stereocilia, as well as transporting cargoes within them. Here, we identify a binding protein for Drosophila myosin-7a termed M7BP, and describe how M7BP assembles myosin-7a into a motile complex that enables cargo translocation and actin cytoskeletal remodeling. M7BP binds to the autoinhibitory tail of myosin-7a, extending the molecule and activating its ATPase activity. Single-molecule reconstitution show that M7BP enables robust motility by complexing with myosin-7a as 2:2 translocation dimers in an actin-regulated manner. Meanwhile, M7BP tethers actin, enhancing complex’s processivity and driving actin-filament alignment during processive runs. Finally, we show that myosin-7a-M7BP complex assembles actin bundles and filopodia-like protrusions while migrating along them in living cells. Together, these findings provide insights into the mechanisms by which myosin-7a functions in actin protrusions.

Proprioceptive Genes as a Source of Genetic Variation Underlying Robustness for Flight Performance inDrosophila

“…The latter corresponded with two separate genes, Myosin-7a binding protein (M7BP; intron) and antisense RNA:CR45131 (704 bp upstream). Interestingly, M7BP localizes to actin-bundles in sensory organs in Drosophila, as well as the Johnston's organ, which is used for auditory sensation (KIEHART et al 2004;TODI et al 2005;TODI et al 2008;LIU et al 2021). The connection between na and M7BP supports the importance of sensory hairs in proprioception and receiving external stimuli during flight that may modulate robustness.…”

Comparative analysis of the MyTH4-FERM myosins reveals insights into the determinants of actin track selection in polarized epithelia

“…It is important to note, however, that there are examples of Class 7 myosins from other species that exhibit tracking to the tips of filopodia-like protrusions. A forced dimer of Drosophila Myo7A motor-neck induces filopodia and tracks to their tips in Drosophila S2 cells (Liu et al, 2021), similar to the single Class 7 myosin found in Dictyostelium that creates and tracks to the tips of filopodia-like protrusions in the social amoebae (Arthur et al, 2019). Going forward, it may be informative to express these examples of Class 7 myosins along with their cognate light chains in an epithelial cell system to observe whether they exhibit motility and assess what type of actin network they are biased towards.…”

“…Myo7A is thought to exist in an autoinhibited conformation in which the tail domain folds back to silence motor activity (Umeki et al, 2009;Yang et al, 2009). Evidence suggests that cargo binding to the tail relieves inhibition, providing a mechanism for correct temporal activation of Myo7A in cells (Sakai et al, 2011;Liu et al, 2021). We reasoned that the lack of targeting of full-length Myo7A could result from either its motor domain not being 'compatible' with using BB actin as a track (perhaps due to differences in actin crosslinking proteins found between BB and stereocilia that could impact actin structure), or that Myo7A was not being properly activated in enterocytes due to lack of correct cargo for its tail domain.…”

VASP-mediated actin dynamics activate and recruit a filopodia myosin

“…MF myosins are thought to act during initiation by cross-linking actin filaments ( Tokuo et al, 2007 ), perhaps zipping them together as the motors walk up the filament toward the cortex ( Berg and Cheney, 2002 ; Ropars et al, 2016 ). Support for this model comes from the observation that forced dimers of motors can induce filopodia or filopodia-like protrusions in cells ( Tokuo et al, 2007 ; Arthur et al, 2019 ; Masters and Buss, 2017 ; Liu et al, 2021 ). Myo10 has also been implicated in elongation by transporting VASP toward the tip of the growing filopodium to promote continued growth ( Tokuo and Ikebe, 2004 ).…”

“…Opening up of the myosin followed by dimerization is required for activation of the myosin ( Umeki et al, 2011 ; Sakai et al, 2011 ; Yang et al, 2006 ; Arthur et al, 2019 ). Partner binding mediated by their MyTH4-FERM (MF) domains can typically stabilize the open, activated form of these myosins as well as promote dimerization ( Sakai et al, 2011 ; Arthur et al, 2019 ; Liu et al, 2021 ). The MF domains in these myosins can indeed mediate interaction with partner proteins such as microtubules ( Weber et al, 2004 ; Toyoshima and Nishida, 2007 ; Planelles-Herrero et al, 2016 ) and the cytoplasmic tails of adhesion and signaling receptors ( Hirao et al, 1996 ; Hamada et al, 2000 ; Zhang et al, 2004 ; Zhu et al, 2007 ; Pi et al, 2007 ).…”