Phosphagen kinases (PKs) catalyze a reversible phosphoryl transfer between ATP and various guanidino compounds. In doing so they create a pool of phosphorylated guanidino compounds, phosphagens, from which ATP can be synthesized during periods of large and sudden energy demands. While this family displays conservation of structure and function, they differ in many other aspects, most notably negative cooperativity.* The current study is an attempt to determine the structural basis for negative cooperativity in the phosphagen kinase superfamily. A structural comparison of creatine kinase, which displays negative cooperativity, and glycocyamine kinase, which does not, revealed several potential structural features that may account for negative cooperativity in this family. Of these, the most important was the presence of a histidine at the N-terminus (H6 in Oryctolagus cuniculus muscle creatine kinase), which is observed only in cooperative PKs. This gave way to the H6 hypothesis, which was then used to predict negative cooperativity in some particularly interesting family members. Specifically, a mitochondrial taurocyamine kinase from Arenicola brasiliensis, and a dimeric arginine kinase from Monosiga brevicollis, were functionally examined for negative cooperativity using isothermal titration calorimetry (ITC), where negative cooperativity was predicted in both. The results support this prediction, as both data sets were fit by a two-site binding model where the second dissociation constant was higher than the first. From an evolutionary perspective this suggests that negative cooperativity may have evolved several times throughout the history of phosphagen kinases.
*Negative cooperativity definition: Binding of a ligand to one subunit decreases ligand affinity in the other subunit.
Biochemistry and Molecular Biology
Kerwood, Gentry Jarrett, "Exploring the Structural Basis for Negative Cooperativity in the Phosphagen Kinase Superfamily" (2015). Senior Independent Study Theses. Paper 6594.
Bachelor of Arts
Senior Independent Study Thesis
© Copyright 2015 Gentry Jarrett Kerwood