Modulation of heterotrimeric G protein activity by nucleoside diphosphate kinase
Thomas Wieland & Robert Feil
Nucleoside diphosphate kinases (NDPKs) are NTP/ NDP transphosphorylases and thus important housekeeping enzymes in cellular nucleotide homeostasis. In mammals they form hexamers, mainly consisting of the two predominant isoforms A and B (encoded by Nme1 and Nme2, respectively), but can also contain additional isoforms such as the more lipophilic NDPK-C (encoded by Nme3). Besides their role in cytosolic NTP supply, NDPKs form complexes with a variety of other proteins to fulfill specific functions in subcellular compartments such as the plasma membrane, microfilaments, mitochondria, and the nucleus. With regard to heterotrimeric G proteins and monomeric GTPases like dynamin, NDPKs contribute to the activation of these GTPases by local GTP supply, which is achieved, for example, by complex formation with the Gβγ dimer. In addition to their role as NTP/ NDP transphosphorylases, NDPKs are able to phosphorylate histidine residues of their complex partners and, thereby, exert additional regulatory functions3. For example, NDPKs can bypass classical GPCR-dependent G protein activation via intermediate phosphorylation of His266 in Gβ and initiate non-canonical G protein signaling4. NDPKs are activators of G protein signaling (AGS) through their function, which is distinct from other AGS proteins. The molecular basis of complex formation between NDPKs and G proteins has not been clarified yet, but these data will be required to successfully address the AGS function of NDPKs as potential therapeutic targets.
As the interaction of purified NDPK-C with purified G proteins can be reconstituted in vitro, we will unravel the composition of the NDPK-B/ C oligomers allowing the interaction with different G protein isoforms, We will study the AGS function of NDPK-B/ C complexes mechanistically and validate SanWie3 and its homologs as inhibitors of this process, and test the influence of SanWie3 on NDPK/ cAMP and cGMP signaling in cultured VSMCs and in the vasculature of biosensor expressing mice to reveal its potential as drug for the treatment of hypertension and atherosclerosis.