Changes in temperature affect all biological processes, including the functions of and interactions between proteins that undergo conformational changes during normal physiological processes. Poikilothermic fishes have body temperatures similar to the surrounding environment, and they must overcome the physiological challenges associated with temperature fluctuations during both seasonal and daily tidal cycles. Killifish (Family Fundulidae) have adapted to temperate and tropical environments, making these fish excellent model organisms to study thermal adaptation. The calcium-binding protein, calsequestrin (CSQ) modulates muscle contraction by "soaking-up" calcium pumped into and regulating release of calcium from the sarcoplasmic reticulum. CSQ thus enables rapid muscle relaxation and contraction cycles of fast twitch muscle necessary for burst swimming associated with predator avoidance and prey capture. The dramatic conformational changes CSQ undergoes during calcium-binding and release cycles lead to the following question: Is the calcium buffering ability of CSQ conserved in Fundulus species that have adapted to different environmental, and thus physiological, temperatures? To address this question, the following hypotheses will be tested using molecular and biophysical techniques: (1) CSQ expression is correlated with relaxation and contraction rates along the fast twitch muscle of Fundulus species adapted to different temperatures; (2) CSQ exhibits conserved thermodynamic parameters at the native physiological temperatures of closely related Fundulus species; and (3) Changes in amino acid sequence of CSQ from Fundulus species adapted to different thermal regimes are correlated with physiological temperature and the calcium-binding ability of CSQ. The results of this research will expand understanding of molecular mechanisms responsible for thermal adaptation of organisms to different environments. Funding will enhance the research infrastructure and training of undergraduate and graduate students at Valdosta State University, which serves a large population of minority students and first generation students from the regional area of southern Georgia. In addition, funding will help strengthen relationships with neighboring research universities.
