BIG1 is a binding partner of myosin IXb and regulates its Rho-GTPase activating protein activity

UMMS Affiliation

Department of Physiology

Publication Date


Document Type



ADP-Ribosylation Factor 1; Animals; Cloning, Molecular; DNA, Complementary; Dose-Response Relationship, Drug; Electrophoresis, Polyacrylamide Gel; GTP-Binding Proteins; Guanine Nucleotide Exchange Factors; Humans; Immunoprecipitation; Inhibitory Concentration 50; Kidney; Mutation; Myosins; Plasmids; Protein Binding; Protein Structure, Tertiary; Rats; Recombinant Proteins; Signal Transduction; Time Factors; Two-Hybrid System Techniques; Zinc Fingers; rho GTP-Binding Proteins; rhoA GTP-Binding Protein


Life Sciences | Medicine and Health Sciences


Myosin IXb, a member of the myosin superfamily, is a molecular motor that possesses a GTPase activating protein (GAP) for Rho. Through the yeast two-hybrid screening using the tail domain of myosin IXb as bait we found BIG1, a guanine nucleotide exchange factor for ADP-ribosylation factor (Arf1), as a potential binding partner for myosin IXb. The interaction between myosin IXb and BIG1 was demonstrated by co-immunoprecipitation of endogenous myosin IXb and BIG1 with anti-BIG1 antibodies in normal rat kidney cells. Using the isolated proteins, it was demonstrated that myosin IXb and BIG1 directly bind to each other. Various truncation mutants of the myosin IXb tail domain were produced, and it was revealed that the binding region of myosin IXb to BIG1 is the zinc finger/GAP domain. Interestingly, the GAP activity of myosin IXb was significantly inhibited by the addition of BIG1 with IC(50) of 0.06 microm. The RhoA binding to myosin IXb was inhibited by the addition of BIG1 with the concentration similar to the inhibition of the GAP activity. Likewise, RhoA inhibited the BIG1 binding of myosin IXb. These results suggest that BIG1 and RhoA compete with each other for the binding to myosin IXb, thus resulting in the inhibition of the GAP activity by BIG1. The present study identified BIG1, the Arf guanine nucleotide exchange factor, as a new binding partner for myosin IXb, which inhibited the GAP activity of myosin IXb. The findings raise a concept that the myosin transports the signaling molecule as a cargo that functions as a regulator for the myosin molecule.

DOI of Published Version



J Biol Chem. 2005 Mar 18;280(11):10128-34. Epub 2005 Jan 11. Link to article on publisher's site

Journal/Book/Conference Title

The Journal of biological chemistry

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PubMed ID