High impact information on VMA21

• Vma12p and Vma22p migrated to fractions separate from Vma21p [1].
• In contrast, the proteolipids associate with Vma21p even in the absence of Vma9p [2].
• We found that in vma21Delta cells, the major proteolipid subunit of V0 failed to interact with the 100-kDa V0 subunit, Vph1p, indicating that Vma21p is necessary for V0 assembly [3].
• Analysis of vmaDelta strains showed that binding of V0 subunits to Vma21p was mediated by the proteolipid subunit Vma11p [3].
• An in vitro assay for ER export was used to demonstrate preferential packaging of the fully assembled Vma21p/proteolipid/Vma6p/Vph1p complex into COPII-coated transport vesicles [3].

Biological context of VMA21

• Biogenesis of V0 requires an endoplasmic reticulum (ER)-localized accessory factor, Vma21p [3].

Anatomical context of VMA21

• The product of the VMA21 gene (Vma21p) is an 8.5-kDa integral membrane protein that is not a subunit of the purified V-ATPase complex but instead resides in the endoplasmic reticulum [4].
• Although a Vma21p mutant lacking an ER-retrieval signal remained associated with V0 in the vacuole, this interaction did not affect the assembly of vacuolar V0/V1 complexes [3].
• We conclude that Vma21p is not involved in regulating the interaction between V0 and V1 sectors, but that it has a crucial role in coordinating the assembly of V0 subunits and in escorting the assembled V0 complex into ER-derived transport vesicles [3].
• Immunoprecipitation of Vma21p from wild-type membranes resulted in coimmunoprecipitation of all five V0 subunits [3].
• The yeast vma21 mutant was isolated from a screen to identify mutants defective in V-ATPase function. vma21 mutants fail to assemble the V-ATPase complex onto the vacuolar membrane: peripheral subunits accumulate in the cytosol and the 100-kDa integral membrane subunit is rapidly degraded [4].

Associations of VMA21 with chemical compounds

• Vma21p contains a dilysine motif at the carboxy terminus, and mutation of these lysine residues abolishes retention in the endoplasmic reticulum and results in delivery of Vma21p to the vacuole, the default compartment for yeast membrane proteins [4].

Other interactions of VMA21

• These results indicate that Vma22p, along with Vma21p and Vma12p, form a set of ER proteins required for V-ATPase assembly [5].
• Unexpectedly, yeast strains lacking Vma21p fail to sort the endoplasmic reticulum to Golgi v-SNARE, Bos1p, efficiently into COPII vesicles, yet these vesicles are fully fusion competent [6].

References