Glycogen Synthase Activity in is Partly Controlled by the Functional Ortholog of Gac1p

To adapt to various host microenvironments, the human fungal pathogen possesses the capacity to accumulate and store glycogen as an internal carbohydrate source. In the model yeast , Glc7p and Gac1p are the serine/threonine type 1 protein phosphatase catalytic and regulatory subunits that control glycogen synthesis by altering the phosphorylation state of the glycogen synthase Gsy2p. Despite recent delineation of the glycogen synthesis pathway in , the molecular events driving synthase activation are currently undefined. In this study, using a combination of microbiologic and genetic techniques, we determined that the protein encoded by uncharacterized gene , and not the currently annotated Gac1p, is the major regulatory subunit involved in glycogen synthesis. C1_01140Cp contains a conserved GVNK motif observed across multiple starch/glycogen-binding proteins in various species, and alanine substitution of each residue in this motif significantly impaired glycogen accumulation in . Fluorescent protein tagging and microscopy indicated that C1_01140Cp-GFPy colocalized with Glc7p-tdTomato and Gsy1p-tdTomato accordingly. Co-immunoprecipitation assays further confirmed that C1_01140Cp associates with Glc7p and Gsy1p during glycogen synthesis. Lastly, Δ/Δ exhibited colonization defects in a murine model of vulvovaginal candidiasis. Collectively, our data indicate that uncharacterized C1_01140Cp is the functional ortholog of the PPP1R subunit Gac1p in .IMPORTANCEThe capacity to synthesize glycogen offers microbes metabolic flexibility, including the fungal pathogen . In , dephosphorylation of glycogen synthase by the Glc7p-containing phosphatase is a critical rate-limiting step in glycogen synthesis. Subunits, including Gac1p, target Glc7p to α-1,4-glucosyl primers for efficient Gsy2p synthase activation. However, this process in had not been delineated. Here, we show that the genome encodes for two homologous phosphatase-binding subunits, annotated Gac1p and uncharacterized C1_01140Cp, both containing a GVNK motif required for polysaccharide affinity. Surprisingly, loss of Gac1p only moderately reduced glycogen accumulation, whereas loss of C1_01140Cp ablated it. Fluorescence microscopy and co-immunoprecipitation approaches revealed that C1_01140Cp associates with Glc7p and Gsy1p during glycogen synthesis. Moreover, C1_01140Cp contributed to fungal fitness at the vaginal mucosa during murine vaginitis. Therefore, this work demonstrates that glycogen synthase regulation is conserved in and C1_01140Cp is the functional ortholog of Gac1p.