Native - Calf Thymus
Polymyositosis (PM) and dermatomyositis (DM) are idiopathic inflammatory myopathies. The existence of autoantibodies to nuclear and cytoplasmic antigens, in particular to the aminoacyl-tRNA synthetase group of enzymes, in the sera of up to 89% of patients indicates that these diseases have an autoimmune origin. The most common autoantibody in PM and DM is anti Jo-1, occurring in 15-20% of all myositis patients and about 30% of adult PM patients.
Jo-1 autoantibodies are capable of inhibiting the activity of the target antigen (HRS) and can immunoprecipitate labelled enzyme as well as its specific tRNA. HRS has a molecular weight of 55 kDa in SDS-polyacrylamide electrophoresis, and is believed to exist as a dimer in its native state.
The amino acid sequence of human Jo-1 antigen has been determined by cloning and sequencing its cDNA. It contains three structural motifs typical of class IIa aminoacyl transferases and two signature regions common to histidyl-tRNA synthetases. The human enzyme amino acid sequence shows significant homology to those of the enzymes from yeast (47.5%) and E. coli. It is predicted to have a coiled-coil α-helical structure that is characteristic of many autoantigens and which contains the major autoantigenic epitope.
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