69.2 Saturday, Jan. 5 Time Travel in the Lab: Exploring Thermal Compensation in Antarctic Fish Parvalbumins MOERLAND, TS*; WHITTINGTON, AC; Kent State Univ., Ohio; Florida State Univ., Tallahassee firstname.lastname@example.org
Antarctic notothenioid fishes display a suite of adaptations to their habitat, including proteins that function optimally in the cold. Studies of enzymes have shown that adaptation to temperature is driven by subtle changes in primary structure that lead to changes in conformational flexibility. We have focused on the Ca2+ binding protein parvalbumin (PV) to determine if the enzymatic paradigm of thermal adaptation applies also to non-enzymatic proteins. Characterization of PV from white muscle of Antarctic notothenioids and from temperate zone teleosts reveals that the pattern of thermal sensitivity for PV Ca2+ dissociation constants (Kd) parallels that of Km for many enzyme systems: At common measurement temperatures, PVs from Antarctic fish have a higher Kd than temperate counterparts, but at physiological temperatures function is conserved. Attributing this observation to specific amino acid substitutions is a difficult task as notothenioids are highly diverged from most temperate fishes, meaning that accumulated neutral substitutions can confound a simple analysis by sequence alignment. Accordingly, this work employs ancestral sequence reconstruction and three-dimensional modeling to pinpoint residues possibly responsible for functional adaptation. Reconstruction and modeling suggested that just two amino acid substitutions can lead to the current Ca2+ binding thermal profile of nothenioid PVs. Expression and characterization of the ancestral Antarctic and temperate PVs supports this hypothesis. Hence, thermal adaptation of PV follows the paradigm established for catalytic proteins: The evolutionary loss of just two hydrogen bonds is sufficient to explain the observed thermal phenotype of Antarctic notothenioid PVs.