TY - JOUR
T1 - Charged residue changes in the carboxy-terminus of α-tropomyosin alter mouse cardiac muscle contractility
AU - Gaffin, Robert D.
AU - Gokulan, Kuppan
AU - Sacchettini, James C.
AU - Hewett, Timothy
AU - Klevitsky, Raisa
AU - Robbins, Jeffrey
AU - Muthuchamy, Mariappan
PY - 2004/4/15
Y1 - 2004/4/15
N2 - Striated muscle tropomyosin (TM) is an essential thin filament protein that is sterically and allosterically involved in calcium-mediated cardiac contraction. We have previously shown that overexpressing the β-TM isoform in mouse hearts leads to physiological changes in myocardial relaxation and Ca2+ handling of myofilaments. Two important charge differences in β-TM compared to α-TM are the exchange of serine and histidine at positions 229 and 276 with glutamic acid and asparagine, respectively, imparting a more negative charge to β-TM relative to α-TM. Our hypothesis is that the net charge at specific sites on TM might be a major determinant of its role in modulating cardiac muscle performance and in regulating Ca2+ sensitivity of the myofilaments. To address this, we generated transgenic (TG) double mutation mouse lines (α-TM DM) expressing mutated α-TM at the two residues that differ between α-and β-TM (Ser229Glu + His276Asn). Molecular analyses show 60-88% of the native TM is replaced with α-TM DM in the different TG lines. Work-performing heart analyses show that a-TM DM mouse hearts exhibit decreased rates of pressure development and relaxation (+dP/dt and-dP/dt). Skinned myofibre preparations from the TG hearts indicate a decrease in calcium sensitivity of steady state force. Protein modelling studies show that these two charge alterations in α-TM cause a change in the surface charges of the molecule. Our results provide the first evidence that charge changes at the carboxy-terminal of α-TM alter the functional characteristics of the heart at both the whole organ and myofilament levels.
AB - Striated muscle tropomyosin (TM) is an essential thin filament protein that is sterically and allosterically involved in calcium-mediated cardiac contraction. We have previously shown that overexpressing the β-TM isoform in mouse hearts leads to physiological changes in myocardial relaxation and Ca2+ handling of myofilaments. Two important charge differences in β-TM compared to α-TM are the exchange of serine and histidine at positions 229 and 276 with glutamic acid and asparagine, respectively, imparting a more negative charge to β-TM relative to α-TM. Our hypothesis is that the net charge at specific sites on TM might be a major determinant of its role in modulating cardiac muscle performance and in regulating Ca2+ sensitivity of the myofilaments. To address this, we generated transgenic (TG) double mutation mouse lines (α-TM DM) expressing mutated α-TM at the two residues that differ between α-and β-TM (Ser229Glu + His276Asn). Molecular analyses show 60-88% of the native TM is replaced with α-TM DM in the different TG lines. Work-performing heart analyses show that a-TM DM mouse hearts exhibit decreased rates of pressure development and relaxation (+dP/dt and-dP/dt). Skinned myofibre preparations from the TG hearts indicate a decrease in calcium sensitivity of steady state force. Protein modelling studies show that these two charge alterations in α-TM cause a change in the surface charges of the molecule. Our results provide the first evidence that charge changes at the carboxy-terminal of α-TM alter the functional characteristics of the heart at both the whole organ and myofilament levels.
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U2 - 10.1113/jphysiol.2003.058487
DO - 10.1113/jphysiol.2003.058487
M3 - Article
C2 - 14766940
AN - SCOPUS:2342650787
SN - 0022-3751
VL - 556
SP - 531
EP - 543
JO - Journal of Physiology
JF - Journal of Physiology
IS - 2
ER -