Part of the proton channel of V-ATPases. Essential component of the endosomal pH-sensing machinery. May play a role in maintaining the Golgi functions, such as glycosylation maturation, by controlling the Golgi pH.
The recruitment of the small GTPase Arf6 and ARNO from cytosol to endosomal membranes is driven by V-ATPase-dependent intra-endosomal acidification. The molecular mechanism that mediates this pH-sensitive recruitment and its role are unknown. Here, we demonstrate that Arf6 interacts with the c-subunit, and ARNO with the a2-isoform of V-ATPase. The a2-isoform is targeted to early endosomes, interacts with ARNO in an intra-endosomal acidification-dependent manner, and disruption of this interaction results in reversible inhibition of endocytosis. Inhibition of endosomal acidification abrogates protein trafficking between early and late endosomal compartments. These data demonstrate the crucial role of early endosomal acidification and V-ATPase/ARNO/Arf6 interactions in the regulation of the endocytic degradative pathway. They also indicate that V-ATPase could modulate membrane trafficking by recruiting and interacting with ARNO and Arf6; characteristics that are consistent with the role of V-ATPase as an essential component of the endosomal pH-sensing machinery.
We identified loss-of-function mutations in ATP6V0A2, encoding the a2 subunit of the V-type H+ ATPase, in several families with autosomal recessive cutis laxa type II or wrinkly skin syndrome. The mutations result in abnormal glycosylation of serum proteins (CDG-II) and cause an impairment of Golgi trafficking in fibroblasts from affected individuals. These results indicate that the a2 subunit of the proton pump has an important role in Golgi function.
Interacting selectively and non-covalently with any protein or protein complex (a complex of two or more proteins that may include other nonprotein molecules).
Evidence
1:
Inferred from Physical InteractionIntAct
The recruitment of the small GTPase Arf6 and ARNO from cytosol to endosomal membranes is driven by V-ATPase-dependent intra-endosomal acidification. The molecular mechanism that mediates this pH-sensitive recruitment and its role are unknown. Here, we demonstrate that Arf6 interacts with the c-subunit, and ARNO with the a2-isoform of V-ATPase. The a2-isoform is targeted to early endosomes, interacts with ARNO in an intra-endosomal acidification-dependent manner, and disruption of this interaction results in reversible inhibition of endocytosis. Inhibition of endosomal acidification abrogates protein trafficking between early and late endosomal compartments. These data demonstrate the crucial role of early endosomal acidification and V-ATPase/ARNO/Arf6 interactions in the regulation of the endocytic degradative pathway. They also indicate that V-ATPase could modulate membrane trafficking by recruiting and interacting with ARNO and Arf6; characteristics that are consistent with the role of V-ATPase as an essential component of the endosomal pH-sensing machinery.
An expression cDNA library was constructed from the helper T cell hybridoma, A.1.1, which has been shown to produce constitutively proteins involved in the down regulation of the immune response. From this library we identified and characterized a cDNA clone, J6B7, by screening with a polyclonal antibody specific for secreted immune regulatory proteins. The mRNA for J6B7 is expressed specifically in some T cells, but not in the thymoma BW5147 or liver cells. J6B7 is 2937 nucleotides in length and contains one open reading frame encoding for a peptide of predicted Mr of 98,042. The nucleotide and deduced amino acid sequences of J6B7 did not reveal significant homology to any published sequences. Hybridization and translation experiments reveal that the J6B7 can hybrid select mRNA from total RNA isolated from either A.1.1 cells or thymic tissue which can be translated in vitro to a peptide which is bound by a monoclonal antibody (mAb) specific for antigenic determinant(s) shared by immune regulatory proteins. Furthermore, the in vitro translated proteins obtained from A.1.1 cells and thymus showed significant suppression of a mixed lymphocyte reaction (MLR) in a dose dependent manner, reaching maximum suppression of 71% and 89%, respectively. These results suggest that the cDNA, J6B7, codes for an immune regulatory protein.
Transmembrane transport of small molecules REACT_15518
Caution
The N-terminus peptide may increase IL1B secretion by peripheral blood monocytes; however as this region is probably in the cytosol, the in vivo relevance of this observation needs to be confirmed.
Protein involved in the transport of ions. Such proteins are usually transmembrane and mediate a movement of ions across cell membranes. Transport may be passive (facilitated diffusion; down the electrochemical gradient), or active (against the electrochemical gradient). Active transport requires energy which may come from light, oxidation reactions, ATP hydrolysis, or cotransport of other ions or molecules.
Protein involved in the transport of a molecule (metabolite, protein, etc), a ion or an electron across cell membranes, inside the cell or in a tissue fluid.
A reference proteome is a set of protein sequences derived from a complete proteome which constitutes a defined standard for a particular user community. Reference proteomes are manually defined according to a number of criteria. They cover the proteomes of well- studied model organisms and other proteomes of interest for biomedical and biotechnological research. Reference proteomes have been selected to provide broad coverage of the tree of life, and constitute a representative cross-section of the taxonomic diversity to be found within UniProtKB.
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