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A.C. Dose, A.C. Corsa, B. Burnside; Myo3A Binds Specific Phospholipids via IQ Motif–rich Regions in Its Neck and Tail . Invest. Ophthalmol. Vis. Sci. 2005;46(13):1737.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: Myo3A is a class III myosin expressed in photoreceptors and hair cells of the inner ear. In mammals and fish, Myo3A has been localized to photoreceptor inner segments. In isolated fish photoreceptors, Myo3A has been localized specifically to the distal ends of the actin filament bundles of calycal processes. This localization to processes with core actin filament bundles resembles that of Myosin I in intestinal microvilli and hair cell stereocilia. Myosin I has been shown to bind both to actin filaments and to lipids. We therefore wanted to investigate whether Myo3A also possesses lipid–binding capability. Methods: We used a protein–lipid overlay assay to assess binding activity of specific domains of fish Myo3A. Fusion proteins encompassing various domains of Myo3A neck and tail regions, including several combinations of the 9 IQ motifs, were tested by incubating them with various phosphoinositides immobilized on a membrane (PIP stripsTM, Echelon Inc.). Results: The neck (1–4) and tail (5–9) IQ motifs bound to phosphatidylinositol–monophosphates [PI(3)P, PI(4)P and PI(5)P] and phosphatidylinositol–diphosphates [PI(3,4)P2, PI(3,5)P2 and PI(4,5)P2], as well as PI(3,4,5)P3 and phosphatidic acid. In contrast, the tail domain beyond the last IQ motif (including tail homology domains I and II) did not bind to any phospholipids. Interestingly, a similar binding pattern to that of the neck and tail motifs, though somewhat less specific, was observed for a fusion protein containing only the 23 amino acids between IQ motifs 4 and 5. A fusion protein containing IQ motif 4 alone did not bind any phospholipids.Conclusions:These data indicate that Myo3A does have lipid binding capability, and that this binding is mediated at least in part by a region between IQ motifs 4 and 5. These findings suggest that Myo3A may play a role in transporting or localizing lipids within the inner segment and calycal processes of photoreceptors.
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