Inositol polyphosphates (IP) play key roles in eukaryotic cellular function. Using gene deletion analysis and IP and phenotype profiling, we discovered and characterized the IP synthesis pathway in a major human fungal pathogen, Cryptococcus neoformans, and identified IP7 as the most influential product promoting cellular functions important for invasive fungal disease. Very little is known about how IP7 functions at the molecular level. As no bioinformatic tools are available to identify IP7 target proteins, we used custom-made IP7 affinity resins to identify the CDK5 protein complex (Pho85/Pho80/Pho81) of the phosphate acquisition (PHO) pathway as an IP7 target in C. neoformans and showed that IP7 binds specifically to a conserved cluster of positively charged lysine (K) residues (K221,224,228) in the SPX domain of the CDK5 (Pho85) inhibitor, Pho81. Disrupting IP7-SPX domain interaction using site-directed mutagenesis, disrupted assembly of the CDK5 complex, preventing PHO pathway activation and Pi uptake, leading to Pi starvation and loss of virulence in a mouse infection model. This is the first report of an IP7-protein interaction in a pathogenic fungus and the role of IP7 as intermolecular glue in a signaling complex important for regulating phosphate homeostasis.