Two Distinct Vps34 Phosphatidylinositol 3–Kinase Complexes Function in Autophagy and Carboxypeptidase Y Sorting in<i>Saccharomyces cerevisiae</i>

TLDR

Vps30p/Apg6p is essential for both autophagy and CPY sorting, yet its precise role remains unclear despite its known interaction with Apg14p. The study proposes that distinct Vps34p–Vps15p complexes, each associated with specific regulatory proteins, mediate separate membrane trafficking events. Mass spectrometry and co‑immunoprecipitation revealed two distinct Vps34 PtdIns3‑kinase complexes—one containing Apg14p for autophagy and another containing Vps38p for CPY sorting—while Vps30p, Vps34p, and Vps15p are required for both processes and additional mutants suggest a third complex.

Abstract

Vps30p/Apg6p is required for both autophagy and sorting of carboxypeptidase Y (CPY). Although Vps30p is known to interact with Apg14p, its precise role remains unclear. We found that two proteins copurify with Vps30p. They were identified by mass spectrometry to be Vps38p and Vps34p, a phosphatidylinositol (PtdIns) 3–kinase. Vps34p, Vps38p, Apg14p, and Vps15p, an activator of Vps34p, were coimmunoprecipitated with Vps30p. These results indicate that Vps30p functions as a subunit of a Vps34 PtdIns 3–kinase complex(es). Phenotypic analyses indicated that Apg14p and Vps38p are each required for autophagy and CPY sorting, respectively, whereas Vps30p, Vps34p, and Vps15p are required for both processes. Coimmunoprecipitation using anti-Apg14p and anti-Vps38p antibodies and pull-down experiments showed that two distinct Vps34 PtdIns 3–kinase complexes exist: one, containing Vps15p, Vps30p, and Apg14p, functions in autophagy and the other containing Vps15p, Vps30p, and Vps38p functions in CPY sorting. The vps34 and vps15 mutants displayed additional phenotypes such as defects in transport of proteinase A and proteinase B, implying the existence of another PtdIns 3–kinase complex(es). We propose that multiple Vps34p–Vps15p complexes associated with specific regulatory proteins might fulfill their membrane trafficking events at different sites.