Arabidopsis has two functional orthologs of the yeast V-ATPase assembly factor Vma21p.
How individual protein subunits assemble into the higher order structure of a protein complex is not well understood. Four proteins dedicated to the assembly of the V(0) subcomplex of the V-adenosine triphosphatase (V-ATPase) in the endoplasmic reticulum (ER) have been identified in yeast, but their precise mode of molecular action remains to be identified. In contrast to the highly conserved subunits of the V-ATPase, orthologs of the yeast assembly factors are not easily identified based on sequence similarity. We show in this study that two ER-localized Arabidopsis proteins that share only 25% sequence identity with Vma21p can functionally replace this yeast assembly factor. Loss of AtVMA21a function in RNA interference seedlings caused impaired cell expansion and changes in Golgi morphology characteristic for plants with reduced V-ATPase activity, and we therefore conclude that AtVMA21a is the first V-ATPase assembly factor identified in a multicellular eukaryote. Moreover, VMA21p acts as a dedicated ER escort chaperone, a class of substrate-specific accessory proteins so far not identified in higher plants.
Neubert
Christoph
C
Center for Plant Molecular Biology, ZMBP, University of Tübingen, Auf der Morgenstelle 1, 72076 Tübingen, Germany.
Graham
Laurie A
LA
Black-Maier
Eric W
EW
Coonrod
Emily M
EM
Liu
Tzu-Yin
TY
Stierhof
York-Dieter
YD
Seidel
Thorsten
T
Stevens
Tom H
TH
Schumacher
Karin
K
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism*; D018833:Chaperonins / Q000096:biosynthesis* / Q000235:genetics* / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000648:ultrastructure; D006056:Golgi Apparatus / Q000201:enzymology / Q000648:ultrastructure; D049452:Green Fluorescent Proteins / Q000378:metabolism; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D010957:Plasmids; D021122:Protein Subunits; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000648:ultrastructure; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D025262:Vacuolar Proton-Translocating ATPases / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
D029681:Arabidopsis Proteins; C533880:AtVMA21a protein, Arabidopsis; C533881:AtVMA21b protein, Arabidopsis; D008565:Membrane Proteins; D021122:Protein Subunits; D029701:Saccharomyces cerevisiae Proteins; C091909:VMA21 protein, S cerevisiae; D049452:Green Fluorescent Proteins; D018833:Chaperonins; D025262:Vacuolar Proton-Translocating ATPases