Biochemical analysis of inositol phosphate kinases.

Lipid-derived inositol phosphates (IPs) are a complex group of second messengers generated by the sequential phosphorylation of inositol 1,4,5-trisphosphate (IP(3)). Synthetic pathways leading from IP(3) to the formation of inositol tetrakisphosphate IP(4), inositol pentakisphosphate IP(5), inositol hexakisphosphate IP(6), and inositol pyrophosphates PP-IPs have been elucidated in eukaryotes from yeast to human. Studies have attributed a variety of cellular functions to IPs, highlighting the importance of understanding how the pathways for their synthesis are regulated.

Regulation of a cyclin-CDK-CDK inhibitor complex by inositol pyrophosphates.

In budding yeast, phosphate starvation triggers inhibition of the Pho80-Pho85 cyclin-cyclin-dependent kinase (CDK) complex by the CDK inhibitor Pho81, leading to expression of genes involved in nutrient homeostasis. We isolated myo-d-inositol heptakisphosphate (IP7) as a cellular component that stimulates Pho81-dependent inhibition of Pho80-Pho85. IP7 is necessary for Pho81-dependent inhibition of Pho80-Pho85 in vitro.

A conserved family of enzymes that phosphorylate inositol hexakisphosphate.

Inositol pyrophosphates are a diverse group of high-energy signaling molecules whose cellular roles remain an active area of study. We report a previously uncharacterized class of inositol pyrophosphate synthase and find it is identical to yeast Vip1 and Asp1 proteins, regulators of actin-related protein-2/3 (ARP 2/3) complexes. Vip1 and Asp1 acted as enzymes that encode inositol hexakisphosphate (IP6) and inositol heptakisphosphate (IP7) kinase activities.