TY - JOUR
T1 - Alteration of tropomyosin function and folding by a nemaline myopathy-causing mutation
AU - Moraczewska, Joanna
AU - Greenfield, Norma J.
AU - Liu, Yidong
AU - Hitchcock-DeGregori, Sarah E.
N1 - Funding Information:
This research was supported by National Institutes of Health Grants HL-35726 and GM-36326 (to S.E.H-D.) and an American Heart Association Postdoctoral Fellowship, New Jersey Affiliate, to J.M.
PY - 2000/12
Y1 - 2000/12
N2 - Mutations in the human TPM3 gene encoding γ-tropomyosin (α-tropomyosin-slow) expressed in slow skeletal muscle fibers cause nemaline myopathy. Nemaline myopathy is a rare, clinically heterogeneous congenital skeletal muscle disease with associated muscle weakness, characterized by the presence of nemaline rods in muscle fibers. In one missense mutation the codon corresponding to Met-8, a highly conserved residue, is changed to Arg. Here, a rat fast α-tropomyosin cDNA with the Met8Arg mutation was expressed in Escherichia coli to investigate the effect of the mutation on in vitro function. The Met8Arg mutation reduces tropomyosin affinity for regulated actin 30- to 100-fold. Ca2+ -sensitive regulatory function is retained, although activation of the actomyosin S1 ATPase in the presence of Ca2+ is reduced. The poor activation may reflect weakened actin affinity or reduced effectiveness in switching the thin filament to the open, force-producing state. The presence of the Met8Arg mutation severely, but locally, destabilizes the tropomyosin coiled coil in a model peptide, and would be expected to impair end-to-end association between TMs on the thin filament. In muscle, the mutation may alter thin filament assembly consequent to lower actin affinity and altered binding of the N-terminus to tropomodulin at the pointed end of the filament. The mutation may also reduce force generation during activation.
AB - Mutations in the human TPM3 gene encoding γ-tropomyosin (α-tropomyosin-slow) expressed in slow skeletal muscle fibers cause nemaline myopathy. Nemaline myopathy is a rare, clinically heterogeneous congenital skeletal muscle disease with associated muscle weakness, characterized by the presence of nemaline rods in muscle fibers. In one missense mutation the codon corresponding to Met-8, a highly conserved residue, is changed to Arg. Here, a rat fast α-tropomyosin cDNA with the Met8Arg mutation was expressed in Escherichia coli to investigate the effect of the mutation on in vitro function. The Met8Arg mutation reduces tropomyosin affinity for regulated actin 30- to 100-fold. Ca2+ -sensitive regulatory function is retained, although activation of the actomyosin S1 ATPase in the presence of Ca2+ is reduced. The poor activation may reflect weakened actin affinity or reduced effectiveness in switching the thin filament to the open, force-producing state. The presence of the Met8Arg mutation severely, but locally, destabilizes the tropomyosin coiled coil in a model peptide, and would be expected to impair end-to-end association between TMs on the thin filament. In muscle, the mutation may alter thin filament assembly consequent to lower actin affinity and altered binding of the N-terminus to tropomodulin at the pointed end of the filament. The mutation may also reduce force generation during activation.
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U2 - 10.1016/S0006-3495(00)76554-4
DO - 10.1016/S0006-3495(00)76554-4
M3 - Article
C2 - 11106625
AN - SCOPUS:0033638660
VL - 79
SP - 3217
EP - 3225
JO - Biophysical Journal
JF - Biophysical Journal
SN - 0006-3495
IS - 6
ER -