P06 : Posttranslational modification of glyceraldehyde-3-phosphate dehydrogenase from a hibernating mammal: Insight into cold-adaptation and structural diversity of a housekeeping enzyme

Abstract

Thirteen-lined ground squirrels, Spermophilus tridecemlineatus, endure cold winters by entering into hibernation; a period that entails extended bouts of aerobic torpor where body temperature drops to near freezing and metabolic rate falls to ∼5% of normal levels. The drastic depression in metabolic rate during torpor is brought about through dramatic changes to cellular biochemistry. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a ubiquitous enzyme that is critical, not only to glucose metabolism, but to a variety of cellular processes including oxidative stress response, autophagy and gene regulation. Its functional diversity makes it a potentially important protein during ground squirrel torpor. Analysis of purified skeletal muscle GAPDH from control and hibernating ground squirrels revealed two structurally diverse proteins. GAPDH from both conditions were extensively modified posttranslationally, with significantly decreased levels of tyrosine phosphorylation, acetylation, and ubiquitination being identified for GAPDH from the torpid condition as compared to control. Furthermore, analysis through mass spectrometry revealed novel acetylation, methylation, dimethylation, oxidation and deamidation sites within the GAPDH protein. The structural diversity of GAPDH matches its functional diversity in the cell and this study begins to correlate these structural differences with changes in GAPDH stability and kinetics during torpor.