Evolution and Functioning of ATP Buffering Systems at the Protist-Metazoan Interface

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Evolution and Functioning of ATP Buffering Systems at the Protist-Metazoan InterfaceW. Ross Ellington, Florida State UniversityAll living cells must produce chemical energy in the form of a substance called adenosine triphosphate- ATP for short. When ATP is broken down, the energy released provides the driving force for such critical cellular processes as biosynthesis, motility and membrane transport. Under certain circumstances, there may be a temporal mismatch of ATP supply and demand as may take place during burst contraction in muscle cells. Alternatively, there may be a spatial mismatch of ATP supply and demand in which the primary sources of ATP, small intracellular structures known as mitochondria, are located large distances in cellular terms from where the ATP is used. Animals have evolved energy storage compounds known as phosphagens that act as ATP buffers. Phosphagens, like phosphoarginine or phosphocreatine, keep ATP levels relatively constant thereby mitigating temporal and spatial mismatches of ATP supply and demand. Arginine kinase (AK) and creatine kinase (CK) are key metabolic enzymes that are agents in the functioning of the above phosphagens. AK and CK are expressed in cells such as muscle fibers, neurons, transport epithelia and primitive-type spermatozoa. The proposed research effort seeks to probe the early functional roles and evolution of AK and CK at the interface of protists and sponges, the oldest, extant metazoan (multi-cellular animals) group. Three central hypotheses are posed- (1) CK evolved from an AK-like ancestor at the dawn of the origin of the metazoans; (2) very early in this lineage, CK evolved into three different CK genes, each coding for unique proteins that are localized in different places in cells; and (3) Both AK and CK function exclusively in spatial ATP buffering in sponges and their protist ancestors; the different CK genes evolved to facilitate this role. The proposed effort will firmly establish the early functional role of phosphagen systems in sponges and what are thought to be their closely related protist allies, the choanoflagellates. The proposed effort will have widespread impact on the training of graduate and undergraduate students, will make major contributions to research infrastructure (sequences, recombinant protein, anti-sera) as well as facilitate key research partnerships, two of which are international.