Abstract
Determining the molecular mechanisms that lead to the development of heart failure will help us gain better insight into the most costly health problem in the Western world. To understand the roles that the actin protein plays in the development of heart failure, we have taken a systematic approach toward characterizing human cardiac actin mutants that have been associated with either hypertrophic or dilated cardiomyopathy. Seven known cardiac actin mutants were expressed in a baculovirus system, and their intrinsic properties were studied. In general, the changes to the properties of the actin proteins themselves were subtle. The R312H variant exhibited reduced stability, with a T m of 53.6°C compared to 56.8°C for WT actin, accompanied with increased polymerization critical concentration and Pi release rate, and a marked increase in nucleotide release rates. Substitution of methionine for leucine at amino acid 305 showed no impact on the stability, nucleotide release rates, or DNase-I inhibition ability of the actin monomer; however, during polymerization, a 2-fold increase in Pi release was observed. Increases to both the T m and DNase-I inhibition activity suggested interactions between E99K actin molecules under monomer-promoting conditions. Y166C actin had a higher critical concentration resulting in a lower Pi release rate due to reduced filament-forming potential. The locations of mutations on the ACTC protein correlated with the molecular effects; in general, mutations in subdomain 3 affected the stability of the ACTC protein or affect the polymerization of actin filaments, while mutations in subdomains 1 and 4 more likely affect protein-protein interactions.
Highlights
Heart failure is a major health problem among developed nations and has been described as the emerging health epidemic of the 21st century [1]
The understanding of the molecular mechanisms involved in hypertrophic cardiomyopathy (HCM) and dilated cardiomyopathy (DCM) development have grown beyond early hypotheses that defective actomyosin force generation causes HCM and altered force transmission leads to DCM [3]
We are establishing if variants of the fundamental cardiac actin protein (ACTC) exhibit changes in their biophysical properties that may contribute to cardiomyopathy development
Summary
Heart failure is a major health problem among developed nations and has been described as the emerging health epidemic of the 21st century [1]. We believe that altered interactions between sarcomere proteins lead to disease states through two related mechanisms: intrinsic instability of the encoded protein, resulting in a reduced level of active protein in the heart, or specific protein interaction changes between the altered protein and binding partners. To test this hypothesis, we are establishing if variants of the fundamental cardiac actin protein (ACTC) exhibit changes in their biophysical properties that may contribute to cardiomyopathy development. Given the often late onset of symptoms, changes in actin activity resulting from these mutations are likely subtle or are overcome by compensatory mechanisms like cardiac remodeling
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