N-terminal Catalytic domain of the Serine/Threonine Kinase, Class IIIB myosin
STKs catalyze the transfer of the gamma-phosphoryl group from ATP to serine/threonine residues on protein substrates. Class IIIB myosin is expressed highly in retina. It is also present in the brain and testis. The human class IIIB myosin gene maps to a region that overlaps the locus for Bardet-Biedl syndrome, which is characterized by dysmorphic extremities, retinal dystrophy, obesity, male hypogenitalism, and renal abnormalities. Class III myosins are motor proteins containing an N-terminal kinase catalytic domain and a C-terminal actin-binding domain. They may play an important role in maintaining the structural integrity of photoreceptor cell microvilli. They may also function as cargo carriers during light-dependent translocation, in photoreceptor cells, of proteins such as transducin and arrestin. The class III myosin subfamily is part of a larger superfamily that includes the catalytic domains of other STKs, protein tyrosine kinases, RIO kinases, aminoglycoside phosphotransferase, choline kinase, and phosphoinositide 3-kinase.
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