ABSTRACT
276 277Estivation is a state of aerobic dormancy used by the desert land snail, Otala lactea, to endure harsh environmental conditions. Paramount to survival in the estivating state is the sustained and profound depression of metabolic rate, which facilitates survival from limited endogenous energy stores for extended periods of time. Metabolic rate depression requires coordinated suppression of ATP-generating and ATP-consuming cellular functions by stable regulatory mechanisms. One such mechanism that has been well-studied in this estivating species is reversible protein phosphorylation. Studies in O. lactea have established that protein phosphorylation has far-reaching regulatory capacity in facilitating the biochemical transition between active and estivating conditions. This mechanism plays a role in modifying the activities of rate-limiting enzymes of carbohydrate metabolism, enhancing intracellular tolerance to oxidative stress, suppressing ATP-intensive processes such as global protein turnover and ion pumping, and activating specific arms of the AMP-activated protein kinase (AMPK) signaling and the insulin signaling cascades. This review chapter will document the evidence suggesting that differential protein phosphorylation, brought about by specific protein kinases and protein phosphatases, is essential to regulating biochemical adaptations in O. lactea that are critical to survival.
