The reference OMIM entry for this protein is 602129

Myosin ixb; myo9b
Myosin, rat, homolog of; myr5

For background information on myosins, see MYO1A (601478).

CLONING

Wirth et al. (1996) isolated cDNAs encoding human myosin IXB (MYO9B) from liver and small intestine libraries. The cDNAs encode a 2,022-amino acid protein with a predicted mass of 229 kD. Like other myosins, MYO9B contains an N-terminal head or motor domain, a neck domain containing 4 tandemly repeated IQ motifs, and a large C-terminal tail. Compared to conventional myosins, the MYO9B head region contains several unusual insertions and the tail region contains a putative GTPase-activating protein domain and putative binding domains for zinc and diacylglycerol. MYO9B and its rat homolog, myr5, have regions of significant sequence divergence at their N and C termini. Wirth et al. (1996) suggested that the rat and human cDNAs may represent alternate splice variants. Northern blot analysis revealed that the gene is expressed as an 8-kb transcript with highest levels of expression observed in peripheral blood leukocytes and moderate expression in thymus and spleen. Wirth et al. (1996) found that expression of the MYO9B protein increased 4.7-fold following TPA-induced differentiation of HL-60 myelocytes into macrophage-like cells. Wirth et al. (1996) suggested that MYO9B may have a role in actin-based processes in myeloid cells. Post et al. (1998) identified a long variant of MYO9B that replaces the last 99 amino acids of the sequence reported by Wirth et al. (1996) with a different 228-amino acid C-terminal domain. Immunoblot analysis showed expression of 240- and 228-kD proteins.

MAPPING

Bahler et al. (1997) used fluorescence in situ hybridization to map the MYO9B gene to chromosome 19p13.2-p13.1. Cosmid mapping further refined this localization to 19p13.1, approximately 800 kb proximal to the MEL gene (165040) and approximately 100 kb distal to the ERBAL2 (132880) gene.

GENE FUNCTION

Immunoblot analysis by Post et al. (1998) showed that MYO9B binds calmodulin (CALM1; 114180) through IQ motifs located in its neck domain. Functional analysis indicated that MYO9B is an active motor that, like other CALM1-containing myosins, exhibits maximal velocity of actin filaments in the absence of calcium. Post et al. (1998) concluded that MYO9B contains calmodulin light chains and is a calcium-regulated, mechanochemically active motor that exhibits RHOGAP (see 602732) activity. Inoue et al. (2002) determined that MYO9B, a single-headed myosin, moves processively on actin filaments as a minus-end-directed motor. Thus, like MYO6 (600970), MYO9B moves in the reverse direction. Post et al. (2002) also performed functional analyses and concluded that MYO9B is single-headed and, like MYO5A (160777), is a processive actin-based motor. Using yeast 2-hybrid analysis, coimmunoprecipitation analysis, and in vitro pull-down assays, Saeki et al. (2005) found that rat and human BIG1 (ARFGEF1; 604141) bound the tail domain of MYO9B. BIG1 and MYO9B bound with a 1-to-1 stoichiometry, and mutation analysis showed that BIG1 bound specifically to the zinc finger/GAP domain of MYO9B. Binding of BIG1 to MYO9B interfered with binding of RhoA (165390) to MYO9B and inhibited the Rho-GAP activity of MYO9B in a dose-dependent manner. Likewise, RhoA inhibited binding of BIG1 to MYO9B.

MOLECULAR GENETICS

Celiac disease (212750), one of the best understood immune-related disorders, presents in the small intestine and results from the interplay between multiple genes and glu ... More on the omim web site

Subscribe to this protein entry history

Oct. 20, 2018: Protein entry updated
Automatic update: OMIM entry 602129 was added.

Oct. 19, 2018: Additional information
Initial protein addition to the database. This entry was referenced in Bryk and co-workers. (2017).