tailieunhanh - Báo cáo khoa học: Effects of cardiomyopathic mutations on the biochemical and biophysical properties of the human a-tropomyosin

Mutations in the proteina-tropomyosin (Tm) can cause a disease known as familial hypertrophic cardiomyopathy. In order to understand how such mutations lead to protein dysfunction, three point mutations were introduced into cDNA encoding the human skeletal tropomyosin, and the recombinant Tms were produced at high levels in the yeast Pichia pastoris. Two mutations (A63V and K70T) were located in theN-terminal regionofTmandone (E180G)was located close to the calcium-dependent troponin T binding domain | Eur. J. Biochem. 271 4132-4140 2004 FEBS 2004 doi Effects of cardiomyopathic mutations on the biochemical and biophysical properties of the human a-tropomyosin Eduardo Hilario1 Silvia L. F. da Silva2 Carlos H. I. Ramos2 and Maria Celia Bertolini1 1Instituto de Quimica UNESP Departamento de Bioquimica e Tecnologia Quimica Araraquara Sao Paulo Brazil 2Centro de Biologia Molecular Estrutural Laboratorio Nacional de Luz Sincrotron Campinas Sao Paulo Brazil Mutations in the protein a-tropomyosin Tm can cause a disease known as familial hypertrophic cardiomyopathy. In order to understand how such mutations lead to protein dysfunction three point mutations were introduced into cDNA encoding the human skeletal tropomyosin and the recombinant Tms were produced at high levels in the yeast Pichia pastoris. Two mutations A63V and K70T were located in the N-terminal region of Tm and one E180G was located close to the calcium-dependent troponin T binding domain. The functional and structural properties of the mutant Tms were compared to those of the wild type protein. None of the mutations altered the head-to-tail polymerization although slightly higher actin binding was observed in the mutant Tm K70T as demonstrated in a cosedimentation assay. The mutations also did not change the cooperativity of the thin filament activation by increasing the concentrations of Ca2 . However in the absence of troponin all mutant Tms were less effective than the wild type in regulating the actomyosin subfragment 1 Mg2 ATPase activity. Circular dichroism spectroscopy revealed no differences in the secondary structure of the Tms. However the thermally induced unfolding as monitored by circular dichroism or differential scanning calorimetry demonstrated that the mutants were less stable than the wild type. These results indicate that the main effect of the mutations is related to the overall stability of Tm as a whole and that the mutations have only minor effects .