Probing subunit-subunit interactions in the yeast vacuolar ATPase by peptide arrays

Recent Insights into the Structure, Regulation, and Function of the V-ATPases

The vacuolar (H(+))-ATPases (V-ATPases) are ATP-dependent proton pumps that acidify intracellular compartments and are also present at the plasma membrane. They function in such processes as membrane traffic, protein degradation, virus and toxin entry, bone resorption, pH homeostasis, and tumor cell invasion. V-ATPases are large multisubunit complexes, composed of an ATP-hydrolytic domain (V1) and a proton translocation domain (V0), and operate by a rotary mechanism. This review focuses on recent insights into their structure and mechanism, the mechanisms that regulate V-ATPase activity (particularly regulated assembly and trafficking), and the role of V-ATPases in processes such as cell signaling and cancer. These developments have highlighted the potential of V-ATPases as a therapeutic target in a variety of human diseases.

Structural analysis of the N-terminal domain of subunit a of the yeast vacuolar ATPase (V-ATPase) using accessibility of single cysteine substitutions to chemical modification

The vacuolar ATPase (V-ATPase) is a multisubunit complex that carries out ATP-driven proton transport. It is composed of a peripheral V1 domain that hydrolyzes ATP and an integral V0 domain that translocates protons. Subunit a is a 100-kDa integral membrane protein (part of V0) that possesses an N-terminal cytoplasmic domain and a C-terminal hydrophobic domain. Although the C-terminal domain functions in proton transport, the N-terminal domain is critical for intracellular targeting and regulation of V-ATPase assembly. Despite its importance, there is currently no high resolution structure for subunit a of the V-ATPase. Recently, the crystal structure of the N-terminal domain of the related subunit I from the archaebacterium Meiothermus ruber was reported. We have used homology modeling to construct a model of the N-terminal domain of Vph1p, one of two isoforms of subunit a expressed in yeast. To test this model, unique cysteine residues were introduced into a Cys-less form of Vph1p and their accessibility to modification by the sulfhydryl reagent 3-(N-maleimido-propionyl) biocytin (MPB) was determined. In addition, accessibility of introduced cysteine residues to MPB modification was compared in the V1V0 complex and the free V0 domain to identify residues protected from modification by the presence of V1. The results provide an experimental test of the proposed model and have identified regions of the N-terminal domain of subunit a that likely serve as interfacial contact sites with the peripheral V1 domain. The possible significance of these results for in vivo regulation of V-ATPase assembly is discussed.