Effects of genetic variations in the dystonia protein torsinA: identification of polymorphism at residue 216 as protein modifier.
Four naturally occurring sequence variations have been found in the coding region of the DYT1 gene encoding torsinA. One of these, a 3 bp (DeltaGAG) deletion, underlies dominantly inherited cases of early-onset torsion dystonia. Others, including a single nucleotide polymorphism that replaces aspartic acid (D) at residue 216 with histidine (H) in 12% of normal alleles and two other rare deletions, have not been clearly associated with disease. To gain insight into how these sequence variations affect torsinA, we used the structure of the related protein ClpB to provide a model of torsinA's AAA+ domain. Motifs important for ATP hydrolysis-sensor 1 and sensor 2-were identified, mutagenized and used to validate predictions of this model. Inspection revealed that the DeltaGAG deletion associated with dystonia removes one residue from an alpha-helix in the C-terminal portion of the AAA+ domain. The resulting distortion in torsinA structure may underlie this mutant's known tendency to produce ER-derived inclusions as well as its proposed loss of function. The D/H polymorphism at residue 216 falls in the N-terminal portion of the AAA+ domain near the sensor 1 motif. Surprisingly, cells expressing torsinA with the polymorphic histidine developed inclusions similar to those associated with DeltaGAG-torsinA, indicating that this change may also affect torsinA structure. Introducing H216 into DeltaGAG-torsinA reduced its tendency to form inclusions, suggesting that the two changes offset each other. Our findings point to a structural basis for the defects associated with the disease-linked DeltaGAG deletion in torsinA. They also suggest possible connections between the allelic polymorphism at residue 216 and the penetrance of DYT1 dystonia, as well as a possible role for this polymorphism in related disease states.
Kock
Norman
N
Department of Neurology, Massachusetts General Hospital, Boston, MA 02114, USA.
Naismith
Teresa V
TV
Boston
Heather E
HE
Ozelius
Laurie J
LJ
Corey
David P
DP
Breakefield
Xandra O
XO
Hanson
Phyllis I
PI
D000251:Adenosine Triphosphatases / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D002478:Cells, Cultured; D004421:Dystonia / Q000235:genetics*; D049071:Endopeptidase Clp; D029968:Escherichia coli Proteins / Q000235:genetics; D005347:Fibroblasts / Q000378:metabolism; D014644:Genetic Variation; D006360:Heat-Shock Proteins / Q000235:genetics; D006801:Humans; D051379:Mice; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000235:genetics* / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D012516:Osteosarcoma / Q000378:metabolism; D011110:Polymorphism, Genetic; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D013329:Structure-Activity Relationship; D014162:Transfection; D014407:Tumor Cells, Cultured
D029968:Escherichia coli Proteins; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; C108175:TOR1A protein, human; D049071:Endopeptidase Clp; D000251:Adenosine Triphosphatases; C069775:ClpB protein, E coli