Charged residue alterations in the inner-core domain and carboxy-terminus of alpha-tropomyosin differentially affect mouse cardiac muscle contractility.
Two important charge differences between the alpha- and beta-tropomyosin (TM) isoforms are the exchange of a serine residue in the inner-core region at position 229, and a histidine residue at the carboxy-terminal end at position 276, with glutamic acid and asparagine, respectively. We have recently shown that altering these two residues in alpha-TM to their beta-TM counterparts in transgenic (TG) mouse hearts causes a depression in both +dP/dt and -dP/dt and a decrease in calcium sensitivity. In this study, we address whether independent charge changes at these two residues in alpha-TM modulate cardiac function differentially. To test this hypothesis we generated two TG lines: alpha-TMSer229Glu and alpha-TMHis276Asn. Molecular analyses show that 98% of native alpha-TM is replaced by mutated protein in alpha-TM229 hearts whereas alpha-TM276 hearts show 82% replacement with the mutated protein. Isolated working heart data show that alpha-TM229 TG hearts exhibit a significant decrease in both +dP/dt (7%) and -dP/dt (8%) compared with nontransgenics (NTGs) and time to peak pressure (TPP) is also reduced in alpha-TM229 hearts. alpha-TM276 hearts show a decrease only in -dP/dt (14%) and TPP is increased. pCa(2+)-tension relationships in skinned fibre preparations indicate decreased calcium sensitivity in alpha-TM229 but no change in alpha-TM276 preparations. Force-[Ca(2+)](IC) measurements from intact papillary fibres indicate that alpha-TM276 fibres produce more force per given [Ca(2+)](IC) when compared to NTG fibres, while alpha-TM229 fibres produce less force per given [Ca(2+)](IC). These data demonstrate that changing charged residues at either the inner-core domain or the carboxyl end of TM alters sarcomeric performance differently, suggesting that the function of TM is compartmentalized along its length.
Gaffin
Robert D
RD
Cardiovascular Research Institute and Department of Medical Physiology, College of Medicine, Texas A & M University System Health Science Center, 336 Reynolds Medical Building, College Station, TX 77843-1114, USA.
Tong
Carl W
CW
Zawieja
David C
DC
Hewett
Timothy E
TE
Klevitsky
Raisa
R
Robbins
Jeffrey
J
Muthuchamy
Mariappan
M
D000818:Animals; D002118:Calcium / Q000502:physiology; D015870:Gene Expression; D051379:Mice; D008822:Mice, Transgenic; D016297:Mutagenesis, Site-Directed; D009200:Myocardial Contraction / Q000235:genetics / Q000502:physiology*; D009206:Myocardium / Q000473:pathology; D010641:Phenotype; D014335:Tropomyosin / Q000737:chemistry / Q000235:genetics / Q000502:physiology*
D014335:Tropomyosin; D002118:Calcium