Sometimes we all need a friend to lean on and help us out. If we’re as lucky as myosin IIIB, we have an espin-1 in our lives to help us get to where we need to be, both literally and figuratively. And if we’re super lucky, that espin-1 will share a glass of wine and watch this week’s Parks and Recreation with us. Today’s stunning image is from a paper describing a fascinating relationship between a myosin motor and its cargo.
Myosin is a molecular motor that walks along actin filaments. There are many types of myosins that have different functions, carry different cargoes, and use different mechanisms to perform their task. One myosin that plays a role in human hearing, MYO3A, uses both its motor and actin-binding tail domains to walk like an inchworm to the ends of actin-based membrane protrusions called filopodia. A recent paper finds that another myosin called MYO3B can reach the tips of filopodia, but needs the help of a protein called espin-1. MYO3B does not have a tail domain like MYO3A, but according to Merritt and colleagues, can use espin-1 cargo as a “crutch” to reach filopodia tips. espin-1 does have an actin-binding domain, suggesting that for some modes of myosin motility, the myosin’s actin-binding tail domain can be replaced with cargo containing an actin-binding domain. In addition, both MYO3A and MYO3B can elongate actin protrusions. In the images above, MYO3B and espin-1 together localize to the tips of filopodia (actin is blue).
Merritt, R., Manor, U., Salles, F., Grati, M., Dose, A., Unrath, W., Quintero, O., Yengo, C., & Kachar, B. (2012). Myosin IIIB Uses an Actin-Binding Motif in Its Espin-1 Cargo to Reach the Tips of Actin Protrusions Current Biology, 22 (4), 320-325 DOI: 10.1016/j.cub.2011.12.053
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