Biology subjects

Bartsch, S. M.

Publications and source records attributed to Bartsch, S. M..

3 recordsLinked to original sources

bioRxiv2024

A GAF domain mediates inositol pyrophosphate substrate channeling in PPIP5K phosphatases

Inositol pyrophosphates (PP-InsPs) are highly phosphorylated nutrient messengers. The final step of their biosynthesis is catalyzed by diphosphoinositol pentakisphosphate kinase (PPIP5K) enzymes, which are conserved among fungi, plants, and animals. PPIP5Ks contain an N-terminal kinase domain that generates the active messenger 1,5-InsP8 and a C-terminal phosphatase domain that participates in PP-InsP catabolism. The balance between kinase and phosphatase activities controls the cellular levels and signaling capacity of 1,5-InsP8. Here, we present crystal structures of the apo and substrate-bound Vip1 phosphatase domain from S. cerevisiae (ScVip1PD). ScVip1PD is a phytase-like inositol 1-pyrophosphate phosphatase with two conserved histidine phosphatase catalytic motifs. The enzyme has a strong preference for 1,5-InsP8 and is inhibited by inorganic phosphate. ScVip1PD has an -helical insertion domain stabilized by a structural Zn2+ binding site, and a unique GAF signaling domain that exists in an open and closed state, allowing channeling of the 1,5-InsP8 substrate to the active site. Mutations that alter the active site, that restrict the movement of the GAF domain or that modify the charge of the substrate channel, significantly inhibit the activity of the yeast enzyme in vitro, and the function of the Arabidopsis PPIP5K VIH2 in planta. Structural analyses of full-length PPIP5Ks suggest that the kinase and phosphatase are independent enzymatic modules. Taken together, our work reveals the structure, enzymatic mechanism and regulation of eukaryotic PPIP5K phosphatases.

biochemistry↗

bioRxiv2024

Inositol pyrophosphate catabolism by three families of phosphatases controls plant growth and development

Inositol pyrophosphates (PP-InsPs) are nutrient messengers whose cellular concentration must be tightly regulated. Diphosphoinositol pentakisphosphate kinases (PPIP5Ks) generate the active signaling molecule 1,5-InsP8. PPIP5Ks contain additional phosphatase domains involved in PP-InsP catabolism. Plant and Fungi Atypical Dual Specificity Phosphatases (PFA-DSPs) and NUDIX phosphatases (NUDTs) also hydrolyze PP-InsPs. Here we dissect the relative contributions of the three different phosphatase families to plant PP-InsP catabolism and nutrient signaling. We report the biochemical characterization of inositol pyrophosphate phosphatases from Arabidopsis and Marchantia polymorpha. Overexpression of different PFA-DSP and NUDT enzymes affects PP-InsP levels and leads to stunted growth phenotypes in Arabidopsis. nudt17/18/21 knock-out mutants have altered PP-InsP pools and gene expression patterns, but no apparent growth defects. In contrast, Marchantia polymorpha Mppfa-dsp1ge, Mpnudt1ge and Mpvip1ge mutants display severe growth and developmental phenotypes associated with changes in cellular PP-InsP levels. Analysis of Mppfa-dsp1geand Mpvip1ge supports a role for PP-InsPs in Marchantia phosphate signaling, and additional functions in nitrate homeostasis and cell wall biogenesis. Simultaneous removal of two phosphatase activities enhances the observed growth phenotypes. Taken together, PPIP5K, PFA-DSP and NUDT inositol pyrophosphate phosphatases play important roles in growth and development by collectively shaping plant PP-InsP pools. Author summaryOrganisms must maintain adequate levels of nutrients in their cells and tissues. One such nutrient is phosphorus, an essential building block of cell membranes, nucleic acids and energy metabolites. Plants take up phosphorus in the form of inorganic phosphate and require sufficient cellular phosphate levels to support their growth and development. It has been shown that plants and other eukaryotic organisms "measure" cellular phosphate levels using inositol pyrophosphate signaling molecules. The concentration of inositol pyrophosphates serves as a proxy for the cellular concentration of inorganic phosphate, and therefore inositol pyrophosphate synthesis and degradation must be tightly regulated. Here, we report that three different families of enzymes contribute to the degradation of inositol pyrophosphates in plants. The different phosphatases together shape cellular inositol pyrophosphate pools and thereby affect inorganic phosphate levels. Loss-of-function mutants of the different enzymes display additional defects in nitrate levels and cell wall architecture, suggesting that inositol pyrophosphates regulate cellular processes beyond inorganic phosphate homeostasis.

plant biology↗

bioRxiv2022

Inositol pyrophosphate-controlled kinetochore architecture and mitotic entry in S. pombe

Inositol pyrophosphates (IPPs) comprise a specific class of signaling molecules that regulate central biological processes in eukaryotes. The conserved Vip1/PPIP5K family controls intracellular IP8 levels, the highest phosphorylated form of IPPs present in yeasts, as it has both inositol kinase and pyrophosphatase activities. Previous studies have shown that the fission yeast S. pombe Vip1/PPIP5K family member Asp1 impacts chromosome transmission fidelity via modulation of spindle function. We now demonstrate that an IP8 analogue is targeted by endogenous Asp1 and that cellular IP8 is subject to cell cycle control. Mitotic entry requires Asp1 kinase function and IP8 levels are increased at the G2/M transition. In addition, the kinetochore, the conductor of chromosome segregation assembled on chromosomes is modulated by IP8. Members of the yeast CCAN kinetochore-subcomplex such as Mal2/CENP-O localize to the kinetochore depending on the intracellular IP8-level: higher than wild-type IP8 levels reduces Mal2 kinetochore targeting, while a reduction in IP8 has the opposite effect. As our perturbations of the inositol polyphosphate and IPP pathways demonstrate that kinetochore architecture depends solely on IP8 and not on other IPPs, we conclude that chromosome transmission fidelity is controlled by IP8 via an interplay between entry into mitosis, kinetochore architecture and spindle dynamics.

cell biology↗