A motif in human histidyl-tRNA synthetase which is shared among several aminoacyl-tRNA synthetases is a coiled-coil that is essential for enzymatic activity and contains the major autoantigenic epitope.
In myositis, disease-specific autoantibodies may be directed against an aminoacyl-tRNA synthetase, usually histidyl-tRNA synthetase. To explore the basis for this phenomenon, we have made recombinant histidyl-tRNA synthetase in the baculovirus system. It was enzymatically active and recognized by human autoantibodies. A truncated protein lacking the first 60 amino acids was inactive as an antigen and as an enzyme. This region is within the first two exons, is predicted to have a coiled-coil configuration, and is found in some other synthetases but not in Escherichia coli or yeast histidyl-tRNA synthetase. Circular dichroism showed that the peptides from this region (amino acids 1-60 and 1-47) have the predicted high alpha-helical content, but smaller fragments (1-30, 14-45, and 31-60) do not. The peptides with a high alpha-helical content could inhibit autoantibodies almost completely, whereas the smaller peptides were unable to do so. The amino acid sequence of this coiled-coil domain in human histidyl-tRNA synthetase resembles the sequence of the extended this coiled-coil arm near the NH2 terminus of bacterial seryl-tRNA synthetase as well as similar regions in some eukaryotic aminoacyl-tRNA synthetases, raising the possibility that this domain serves a similar tRNA-stabilizing role and has been preserved from a common ancestor.
Raben
N
N
Connective Tissue Diseases Section, NIAMSD, National Institutes of Health, Bethesda, Maryland 20892.
Nichols
R
R
Dohlman
J
J
McPhie
P
P
Sridhar
V
V
Hyde
C
C
Leff
R
R
Plotz
P
P
D000595:Amino Acid Sequence; D000604:Amino Acyl-tRNA Synthetases / Q000737:chemistry*; D000818:Animals; D001323:Autoantibodies / Q000097:blood / Q000276:immunology; D001324:Autoantigens / Q000737:chemistry* / Q000276:immunology; D016367:Baculoviridae / Q000235:genetics; D002478:Cells, Cultured; D000939:Epitopes / Q000737:chemistry* / Q000276:immunology; D005091:Exons; D006643:Histidine-tRNA Ligase / Q000737:chemistry* / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification; D006801:Humans; D008969:Molecular Sequence Data; D009036:Moths; D011487:Protein Conformation; D011994:Recombinant Proteins
D001323:Autoantibodies; D001324:Autoantigens; D000939:Epitopes; D011994:Recombinant Proteins; D000604:Amino Acyl-tRNA Synthetases; D006643:Histidine-tRNA Ligase