The kinetic properties of a human PPIP5K reveal that its kinase activities are protected against the consequences of a deteriorating cellular bioenergetic environment

33Citations
Citations of this article
38Readers
Mendeley users who have this article in their library.

Abstract

We obtained detailed kinetic characteristics - stoichiometry, reaction rates, substrate affinities and equilibrium conditions - of human PPIP5K2 (diphosphoinositol pentakisphosphate kinase 2). This enzyme synthesizes 'highenergy' PP -InsP s (diphosphoinositol polyphosphates) by metabolizing InsP6 (inositol hexakisphosphate) and 5-InsP7 (5-diphosphoinositol 1,2,3,4,6-pentakisphosphate) to 1-InsP 7 (1-diphosphoinositol 2,3,4,5,6-pentakisphosphate) and InsP8 (1,5-bis-diphosphoinositol 2,3,4,6-tetrakisphosphate), respectively. These data increase our insight into the PPIP5K2 reaction mechanism and clarify the interface between PPIP5K catalytic activities and cellular bioenergetic status. For example, stochiometric analysis uncovered non-productive, substrate-stimulated ATPase activity (thus, approximately 2 and 1.2 ATP molecules are utilized to synthesize each molecule of 1-InsP7 and InsP8, respectively). Impaired ATPase activity of a PPIP5K2-K248A mutant increased atomic-level insight into the enzyme's reaction mechanism. We found PPIP5K2 to be fully reversible as an ATP-synthase in vitro, but our new data contradict previous perceptions that significant 'reversibility' occurs in vivo. PPIP5K2 was insensitive to physiological changes in either [AMP] or [ATP]/[ADP] ratios. Those data, together with adenine nucleotide kinetics (ATP Km = 20-40 μM), reveal how insulated PPIP5K2 is from cellular bioenergetic challenges. Finally, the specificity constants for PPIP5K2 revise upwards by one-to-two orders of magnitude the inherent catalytic activities of this enzyme, and we show its equilibrium point favours 80-90% depletion of InsP6/5-InsP7. © 2013 The Author(s).

Cite

CITATION STYLE

APA

Weaver, J. D., Wang, H., & Shears, S. B. (2013). The kinetic properties of a human PPIP5K reveal that its kinase activities are protected against the consequences of a deteriorating cellular bioenergetic environment. Bioscience Reports, 33(2), 229–242. https://doi.org/10.1042/BSR20120115

Register to see more suggestions

Mendeley helps you to discover research relevant for your work.

Already have an account?

Save time finding and organizing research with Mendeley

Sign up for free