GROVE, T.J.*; MOERLAND, T.S.; Florida State University,; Florida State University: Troponin C isoforms from Fundulus sp. adapted to different thermal regimes are highly conserved

Fundulus are small intertidal fish adapted to a wide variety of thermal environments in coastal waters of North America. Fundulus heteroclitus populations experience different mean annual temperatures along a latitudinal cline (1 per degree latitude) and rapid fluctuations during tidal cycles (up to 15C in less than an hour). Two congeneric species, Fundulus grandis and Fundulus similis, are found in warm (22-26C) coastal waters of the Gulf of Mexico. Troponin, a protein complex composed of three subunits, initiates muscle contraction when the troponin C (TnC) subunit binds calcium. Because of the differences in mean annual and daily tidal temperatures of these closely related fish species, we asked if the amino acid sequences, and potentially calcium-binding properties of TnC (and the troponin complex), are conserved between populations of F. heteroclitus and Fundulus sp. that have adapted to different environmental, and thus physiological, temperatures. Full-length amino acid sequences of cardiac and fast skeletal muscle troponin C were determined and compared between northern and southern populations of F. heteroclitus, F. similis and F. grandis. Analysis of deduced amino acid sequences of the troponin C isoforms indicate high percent identity between Fundulus species (98-99%), and northern and southern populations of F. heteroclitus share 100% sequence identity. Functional analysis is currently underway to measure the thermodynamic and kinetic properties of TnC to determine how temperature affects TnC function. Other mechanisms such as the interaction of contractile regulatory proteins may be critical in maintaining muscle function at variable physiological temperatures. Supported by AHA postdoctoral fellowship 0425339B to T.J.G.