Mammalian class E Vps proteins, SBP1 and mVps2/CHMP2A, interact with and regulate the function of an AAA-ATPase SKD1/Vps4B.
SKD1 belongs to the AAA-ATPase family and is one of the mammalian class E Vps (vacuolar protein sorting) proteins. Previously we have reported that the overexpression of an ATPase activity-deficient form of SKD1 (suppressor of potassium transport growth defect), SKD1(E235Q), leads the perturbation of membrane transport through endosomes and lysosomes, however, the molecular mechanism behind the action of SKD1 is poorly understood. We have identified two SKD1-binding proteins, SBP1 and mVps2, by yeast two-hybrid screening and we assign them as mammalian class E Vps proteins. The primary sequence of SBP1 indicates 22.5% identity with that of Vta1p from Saccharomyces cerevisiae, which was recently identified as a novel class E Vps protein binding to Vps4p. In fact, SBP1 binds directly to SKD1 through its C-terminal region (198-309). Endogenous SBP1 is exclusively localized to cytosol, however it is redirected to an aberrant endosomal structure, the E235Q compartment, in the cells expressing SKD1(E235Q). The ATPase activity of SKD1 regulates both the membrane association of, and assembly of, a large hetero-oligomer protein complex, containing SBP1, which is potentially involved in membrane transport through endosomes and lysosomes. The N-terminal half (1-157) of human SBP1 is identical to lyst-interacting protein 5 and intriguingly, SKD1 ATPase activity significantly influences the membrane association of lyst protein. The SKD1-SBP1 complex, together with lyst protein, may function in endosomal membrane transport. A primary sequence of mVps2, a mouse homologue of human CHMP2A/BC-2, indicates 44.4% identity with Vps2p/Did4p/Chm2p from Saccharomyces cerevisiae. mVps2 also interacts with SKD1 and is localized to the E235Q compartment. Intriguingly, the N-terminal coiled-coil region of mVps2 is required for the formation of the E235Q compartment but not for binding to SKD1. We propose that both SBP1 and mVps2 regulate SKD1 function in mammalian cells.
Fujita
Hideaki
H
Division of Pharmaceutical Cell Biology, Kyushu University Graduate School of Pharmaceutical Sciences, Maidashi 3-1-1, Higashi-ku, Fukuoka 812-8582, Japan. fujita@bioc.phar.kyushu-u.ac.jp
Umezuki
Yusuke
Y
Imamura
Kanako
K
Ishikawa
Daisuke
D
Uchimura
Seiko
S
Nara
Atsuki
A
Yoshimori
Tamotsu
T
Hayashizaki
Yoshihide
Y
Kawai
Jun
J
Ishidoh
Kazumi
K
Tanaka
Yoshitaka
Y
Himeno
Masaru
M
D000074183:ATPases Associated with Diverse Cellular Activities; D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D056827:Endosomal Sorting Complexes Required for Transport; D011992:Endosomes / Q000378:metabolism; D006801:Humans; D007425:Intracellular Membranes / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009154:Mutation; D009928:Organ Specificity; D021381:Protein Transport; D012097:Repressor Proteins / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D020798:Two-Hybrid System Techniques; D033921:Vesicular Transport Proteins / Q000378:metabolism*
C505902:Chmp2a protein, mouse; D056827:Endosomal Sorting Complexes Required for Transport; D008565:Membrane Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D033921:Vesicular Transport Proteins; D000251:Adenosine Triphosphatases; D000074183:ATPases Associated with Diverse Cellular Activities; C490304:VPS4B protein, human