Meeting Abstract

P1.162  Wednesday, Jan. 4  Functional Characterization of Calsequestrin from the Eurythermal Killifish, Fundulus similis GROVE, TJ*; FORT, TJ; Valdosta State University; Valdosta State University tjgrove@valdosta.edu

Calsequestrin (CSQ) is a calcium-binding protein in sarcoplasmic reticulum (SR) that undergoes dramatic conformational changes, changing from a random coil at low Ca²⁺ levels in SR during muscle contraction to highly ordered polymer chains under high Ca²⁺ concentrations during muscle relaxation. We are interested in understanding the mechanisms by which this structurally dynamic protein is able to undergo conformational changes and remain functional in organisms that experience variable physiological temperatures. To this end, we are currently characterizing the function of CSQ from fast twitch muscle of the longnose killifish, Fundulus similis. Using a fluorometric assay to monitor the intrinsic fluorescence of conserved tryptophans, preliminary data indicate the dissociation constant (K_d) of CSQ from F. similis is 544 ± 40 μM at 25°C in the presence of 0.1M KCl and 270 ± 16 μM at 25°C in the absence of KCl. In addition, Ca²⁺-induced polymerization and precipitation of CSQ aggregates at 25°C in the presence of 0.1M KCl was measured using a turbidity assay. The Ca²⁺ concentration at which half maximal precipitation of polymers occurred was 1.72 ± 0.13 mM. Experiments are ongoing to examine the effects of temperature on the calcium-binding ability of CSQ in this eurythermal fish species. This work is supported by National Science Foundation grant IOS-0817805.