Biology subjects

Sakamaki, J.-i.

Publications and source records attributed to Sakamaki, J.-i..

2 recordsLinked to original sources

bioRxiv2023

Syntaxin 17 recruitment to mature autophagosomes is temporally regulated by PI4P accumulation

During macroautophagy, cytoplasmic constituents are engulfed by autophagosomes. Lysosomes fuse with closed autophagosomes but not with unclosed intermediate structures. This is achieved in part by the late recruitment of the autophagosomal SNARE syntaxin 17 (STX17) to mature autophagosomes. However, how STX17 recognizes autophagosome maturation is not known. Here, we show that this temporally regulated recruitment of STX17 depends on the positively charged C-terminal region of STX17. Consistent with this finding, mature autophagosomes are more negatively charged compared with unclosed intermediate structures. This electrostatic maturation of autophagosomes is likely driven by the accumulation of phosphatidylinositol 4-phosphate (PI4P) in the autophagosomal membrane. Accordingly, dephosphorylation of autophagosomal PI4P prevents the association of STX17 to autophagosomes. Furthermore, molecular dynamics simulations support PI4P-dependent membrane insertion of the transmembrane helices of STX17. Based on these findings, we propose a model in which STX17 recruitment to mature autophagosomes is temporally regulated by a PI4P-driven change in the surface charge of autophagosomes.

cell biology↗

bioRxiv2022

The pH-sensing Rim101 pathway regulates cell size in budding yeast

Although cell size regulation is crucial for cellular functions in a variety of organisms, from bacteria to humans, the underlying mechanisms remain elusive. Here, we identify Rim21, a component of the pH-sensing Rim101 pathway, as a positive regulator of cell size through a genome-wide screen of Saccharomyces cerevisiae deletion mutants. We found that mutants defective in the Rim101 pathway were consistently smaller than wild-type cells in the log and stationary phases. The expression of the active form of Rim101 increased the size of wild-type cells. Furthermore, the size of wild-type cells increased in response to external alkalization, which was associated with changes in both vacuolar and cytoplasmic volume. These volume changes were dependent on Rim21 and Rim101. A mutant lacking Vph1, a component of V-ATPase that is transcriptionally regulated by Rim101, was also smaller than wild-type cells, with no increase in size in response to alkalization. The loss of Vph1 suppressed the Rim101-induced increase in cell size under physiological pH conditions. Our results suggest that the cell size of budding yeast is regulated by the Rim101 and V-ATPase axis under physiological conditions as well as in response to alkaline stresses.

cell biology↗