NORMAL GENOMIC

• Todorov PT, Hardisty RE, Brown SD
• Myosin VIIA is specifically associated with calmodulin andmicrotubule-associated protein-2B (MAP-2B).
• Biochem J. 2001; 354: 267-74
• Display abstract

• Myosin VIIA is a motor molecule with a conserved head domain and tailregion unique to myosin VIIA, which probably defines its unique functionin vivo. In an attempt to further characterize myosin VIIA function we setout to identify molecule(s) that specifically associate with it. Wedemonstrate that 17 and 55 kDa proteins from mouse kidney and cochleaco-purify with myosin VIIA on affinity columns carrying immobilizedanti-myosin VIIA antibody. N-terminal sequencing and immunoblottinganalysis identified the 17 kDa protein as calmodulin, whereas MS andimmunoblotting analysis identified the 55 kDa protein asmicrotubule-associated protein-2B (MAP-2B). Myosin VIIA can also beco-immunoprecipitated from kidney homogenate using anti-calmodulin oranti-MAP2 (recognizing isoforms 2A and 2B) antibodies, confirming thestrong association between calmodulin and myosin VIIA and between MAP-2Band myosin VIIA. Myosin VIIA binds to calmodulin with an apparent K(d) of10(-9) M. Scatchard analysis of the binding of myosin VIIA to MAP-2Bprovided evidence for two binding sites, with K(d) values of 10(-10) and10(-9) M, which have been mapped to medial and C-terminal tail domains ofmyosin VIIA. The characterization of the interaction of calmodulin andMAP-2B with myosin VIIA provides new insights into the function of myosinVIIA.

• Weil D et al.
• Defective myosin VIIA gene responsible for Usher syndrome type 1B.
• Nature. 1995; 374: 60-1
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• Usher syndrome represents the association of a hearing impairment withretinitis pigmentosa and is the most frequent cause of deaf-blindness inhumans. It is inherited as an autosomal recessive trait which isclinically and genetically heterogeneous. Some patients show abnormalorganization of microtubules in the axoneme of their photoreceptors cells(connecting cilium), nasal ciliar cells and sperm cells, as well aswidespread degeneration of the organ of Corti. Usher syndrome type 1(USH1) is characterized by a profound congenital sensorineural hearingloss, constant vestibular dysfunction and prepubertal onset of retinitispigmentosa. Of three different genes responsible for USH1. USH1B maps to11q13.5 (ref. 10) and accounts for about 75% of USH1 patients. The mousedeafness shaker-1 (sh1) mutation has been localized to the homologousmurine region. Taking into account the cytoskeletal abnormalities in USHpatients, the identification of a gene encoding an unconventional myosinas a candidate for shaker-1 (ref. 14) led us to consider the humanhomologue as a good candidate for the gene that is defective in USH1B.Here we present evidence that a gene encoding myosin VIIA is responsiblefor USH1B. Two different premature stop codons, a six-base-pair deletionand two different missense mutations were detected in five unrelatedfamilies. In one of these families, the mutations were identified in bothalleles. These mutations, which are located at the amino-terminal end ofthe motor domain of the protein, are likely to result in the absence of afunctional protein. Thus USH1B appears as a primary cytoskeletal proteindefect. These results implicate the genes encoding other unconventionalmyosins and their interacting proteins as candidates for other geneticforms of Usher syndrome.