Neurabin: A Novel Neural Tissue–specific Actin Filament–binding Protein Involved in Neurite Formation

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Abstract
We purified from rat brain a novel actin filament (F-actin)–binding protein of ∼180 kD (p180), which was specifically expressed in neural tissue. We named p180 neurabin (neural tissue–specific F-actin– binding protein). We moreover cloned the cDNA of neurabin from a rat brain cDNA library and characterized native and recombinant proteins. Neurabin was a protein of 1,095 amino acids with a calculated molecular mass of 122,729. Neurabin had one F-actin–binding domain at the NH2-terminal region, one PSD-95, DlgA, ZO-1–like domain at the middle region, a domain known to interact with transmembrane proteins, and domains predicted to form coiled-coil structures at the COOH-terminal region. Neurabin bound along the sides of F-actin and showed F-actin–cross-linking activity. Immunofluorescence microscopic analysis revealed that neurabin was highly concentrated in the synapse of the developed neurons. Neurabin was also concentrated in the lamellipodia of the growth cone during the development of neurons. Moreover, a study on suppression of endogenous neurabin in primary cultured rat hippocampal neurons by treatment with an antisense oligonucleotide showed that neurabin was involved in the neurite formation. Neurabin is a candidate for key molecules in the synapse formation and function.