55.4 Saturday, Jan. 5 From Muscle to Molecule: Function and Structure of the Calcium-Binding Protein Calsequestrin from a Eurythermal Teleost GROVE, T.J.*; WHITTINGTON, A.C.; NIENOW, T.E.; WHITTINGTON, C.L.; FORT, T.J.; Valdosta State University; Florida State University; Valdosta State University; University of South Florida; Valdosta State University email@example.com
Calsequestrins (CSQ) are Ca2+-binding proteins in the sarcoplasmic reticulum (SR) of striated muscles that sequester calcium during muscle relaxation. CSQ undergoes conformational changes from a random coil at low levels of Ca2+ to highly ordered crystalline aggregates at high Ca2+ levels, but the underlying mechanism by which this structurally dynamic protein remains functional in eurythermal organisms is not known. The intertidal mummichog, Fundulus heteroclitus, provides an interesting study system for investigating thermal adaptation. Recorded twitch times of glycolytic skeletal muscle from F. heteroclitus decrease, while force increases, with increasing temperature (5-25ºC). Preliminary data indicate that force production decreases in the presence of the CSQ inhibitor, trifluoperazine, and this effect is more pronounced at higher temperatures. Recombinant CSQ from F. heteroclitus glycolytic muscle (FCSQ) is relatively insensitive to temperature changes in the physiological range (10-25ºC). At 35ºC, Ca2+-binding ability of FCSQ decreases, correlating with a decrease in force production at this higher experimental temperature. Structural modeling of FCSQ reveals a highly conserved salt-bridge network critical for high-capacity Ca2+-binding. The benefits of this work are two-fold: (1) we will be able to deliberately alter the physicochemical properties of FCSQ and measure the functional response to environmental perturbation, and (2) we will correlate the resulting in vitro functional changes with muscle function and whole organism performance. Supported by National Science Foundation grant IOS-0817805.