RAVE and Rabconnectin-3 Complexes as Signal Dependent Regulators of Organelle Acidification

Abstract

The yeast RAVE (Regulator of H+-ATPase of Vacuolar and Endosomal membranes) complex and Rabconnectin-3 complexes of higher eukaryotes regulate acidification of organelles such as lysosomes and endosomes by catalyzing V-ATPase assembly. V-ATPases are highly conserved proton pumps consisting of a peripheral V1 subcomplex that contains the sites of ATP hydrolysis, attached to an integral membrane Vo subcomplex that forms the transmembrane proton pore. Reversible disassembly of the V-ATPase is a conserved regulatory mechanism that occurs in response to multiple signals, serving to tune ATPase activity and compartment acidification to changing extracellular conditions. Signals such as glucose deprivation can induce release of V1 from Vo, which inhibits both ATPase activity and proton transport. Reassembly of V1 with Vo restores ATP-driven proton transport, but requires assistance of the RAVE or Rabconnectin-3 complexes. Glucose deprivation triggers V-ATPase disassembly in yeast and is accompanied by binding of RAVE to V1 subcomplexes. Upon glucose readdition, RAVE catalyzes both recruitment of V1 to the vacuolar membrane and its reassembly with Vo. The RAVE complex can be recruited to the vacuolar membrane by glucose in the absence of V1 subunits, indicating that the interaction between RAVE and the Vo membrane domain is glucose-sensitive. Yeast RAVE complexes also distinguish between organelle-specific isoforms of the Vo a-subunit and thus regulate distinct V-ATPase subpopulations. Rabconnectin-3 complexes in higher eukaryotes appear to be functionally equivalent to yeast RAVE. Originally isolated as a two-subunit complex from rat brain, the Rabconnectin-3 complex has regions of homology with yeast RAVE and was shown to interact with V-ATPase subunits and promote endosomal acidification. Current understanding of the structure and function of RAVE and Rabconnectin-3 complexes, their interactions with the V-ATPase, their role in signal-dependent modulation of organelle acidification, and their impact on downstream pathways will be discussed.

Direct control of lysosomal catabolic activity by mTORC1 through regulation of V-ATPase assembly

“…This suggests that RILP is dispensable for V-ATPase assembly in response to mTORC1 inactivation. Next, we examined DMXL1/2, which appear to be functionally related to the yeast V-ATPase assembly factor, the RAVE complex 25 . Genetic ablation of DMXL1/2 strongly suppressed lysosomal V1B2 and cresyl violet levels under basal and mTORC1-inhibited conditions (Supplementary Fig.…”

“…At the molecular level, V-ATPase assembly has been studied primarily in yeast, where the RAVE complex binds cytosolic V 1 domains and catalyses their assembly with membrane-bound V o domains. In mammalian cells, several proteins have been implicated in V-ATPase assembly, including DMXL1/2, which appear to be functional equivalents of yeast RAVE 25 . V-ATPase assembly and disassembly is controlled by metabolic signals.…”

Chimeric a-subunit isoforms generate functional yeast V-ATPases with altered regulatory properties in vitro and in vivo

“…This region of Rav1 is critical for recruitment of RAVE to the vacuolar membrane, as mutations in a small conserved sequence in the center completely prevent recruitment (Jaskolka & Kane, 2020). The RAVE complex has been proposed to template reassembly of the V-ATPase, and the proximal end of Vph1NT may be a “landing site” for the RAVE complex bearing the V 1 subcomplex and subunit C that could then orient the complexes for reassembly of the active complex (Jaskolka et al, 2021). Binding of RAVE to the proximal end of Vph1NT could leave the distal end free to assemble a quaternary complex with the foot domain of subunit C and the appropriate EG peripheral stalk, which is likely to be a critical step in reassembly (Oot et al, 2017).…”

Role of Lysosomal Acidification Dysfunction in Mesenchymal Stem Cell Senescence

“…Ju-Hyun Lee et al showed that presenilin-1 (PS1) knockout impairs the orientation of v-ATPase V0a1 subunit to the lysosome (Lee et al, 2010). Michael C. Jaskolka et al found that the prokaryotic RAVE and eukaryotic Rabconnectin-3 complexes facilitate the recombination of V1 with V0 during glucose recovery and consequently restore ATPdriven proton transport (Jaskolka et al, 2021). Qing Tang et al reported the absence of the N-deacetylase and N-sulfotransferase 3 (NDST3) promotes the assembly of the V-ATPase holoenzyme on the lysosomal membrane (Tang et al, 2021).…”