ATP6AP1

ATP6AP1 Full Name

ATPase, H+ transporting, lysosomal accessory protein 1

ATP6AP1 Introduction

ATP6AP1, frequently identified in literature by its historical name Ac45, is a highly conserved and essential accessory subunit of the vacuolar-type H+-ATPase (V-ATPase) complex. The V-ATPase is a massive, multi-subunit molecular motor that acts as an ATP-driven proton pump, responsible for acidifying various intracellular compartments, including lysosomes, endosomes, secretory vesicles, and the Golgi apparatus. Within this complex, ATP6AP1 plays an indispensable structural and regulatory role. It guides the proper assembly of the V0 membrane-spanning sector, ensures the structural stability of the entire pump, and orchestrates its precise subcellular targeting. By actively facilitating this continuous proton-pumping activity, ATP6AP1 is critical for maintaining optimal organellar pH. This highly controlled acidic microenvironment is an absolute prerequisite for normal cellular homeostasis, driving processes such as lysosomal degradation, membrane trafficking, receptor recycling, and the proper enzymatic function of resident Golgi glycosyltransferases. Furthermore, in specialized cells like osteoclasts, ATP6AP1-mediated extracellular acidification is strictly required for bone resorption.

Figure 1. A schematic diagram of the luminal view of the glycoproteolipid Vo complex. (Source: Wang L, et al. 2020)

The profound clinical importance of ATP6AP1 is starkly highlighted by the devastating consequences of its genetic disruption. Loss-of-function mutations in the ATP6AP1 gene lead to a rare, systemic metabolic disease known as ATP6AP1-congenital disorder of glycosylation (ATP6AP1-CDG). Because V-ATPase failure compromises Golgi acidification, the cellular glycosylation machinery effectively collapses. Clinically, patients with ATP6AP1-CDG present with a severe, multi-systemic phenotype encompassing primary immunodeficiency, profound hepatopathy, neurocognitive impairment, and cutis laxa (abnormally loose skin due to connective tissue defects). Beyond rare congenital metabolic diseases, the dysregulation of ATP6AP1 and the broader V-ATPase complex is increasingly implicated in oncology. In highly aggressive solid tumors, cancer cells frequently upregulate V-ATPase components to acidify the extracellular tumor microenvironment. This deliberate pathological acidification directly fuels tumor invasion, promotes metastasis, and confers robust resistance to basic chemotherapeutic agents. Thus, ATP6AP1 stands as a vital molecular linchpin bridging cellular pH homeostasis with severe congenital and oncological pathologies.

Alternate Names for ATP6AP1

ATP6AP1; ATPase, H+ transporting, lysosomal accessory protein 1; ATP6IP1, ATP6S1, ATPase, H+ transporting, lysosomal (vacuolar proton pump), subunit 1; V-type proton ATPase subunit S1; 16A; Ac45; CF2; ORF; VATPS1; XAP 3

• 1. Wang L, et al. Structures of a Complete Human V-ATPase Reveal Mechanisms of Its Assembly. Mol Cell. 2020 Nov 5;80(3):501-511.e3.
  2. Jansen EJ, et al. ATP6AP1 deficiency causes an immunodeficiency with hepatopathy, cognitive impairment and abnormal protein glycosylation. Nat Commun. 2016 May 27;7:11600.