Human H+ATPase a4 subunit mutations causing renal tubular acidosis reveal a role for interaction with phosphofructokinase-1

Am J Physiol Renal Physiol. 2008 Oct;295(4):F950-8. doi: 10.1152/ajprenal.90258.2008. Epub 2008 Jul 16.

Abstract

The vacuolar-type ATPase (H+ATPase) is a ubiquitously expressed multisubunit pump whose regulation is poorly understood. Its membrane-integral a-subunit is involved in proton translocation and in humans has four forms, a1-a4. This study investigated two naturally occurring point mutations in a4's COOH terminus that cause recessive distal renal tubular acidosis (dRTA), R807Q and G820R. Both lie within a domain that binds the glycolytic enzyme phosphofructokinase-1 (PFK-1). We recreated these disease mutations in yeast to investigate effects on protein expression, H+ATPase assembly, targeting and activity, and performed in vitro PFK-1 binding and activity studies of mammalian proteins. Mammalian studies revealed complete loss of binding between the COOH terminus of a4 containing the G-to-R mutant and PFK-1, without affecting PFK-1's catalytic activity. In yeast expression studies, protein levels, H+ATPase assembly, and targeting of this mutant were all preserved. However, severe (78%) loss of proton transport but less decrease in ATPase activity (36%) were observed in mutant vacuoles, suggesting a requirement for the a-subunit/PFK-1 binding to couple these two functions. This role for PFK in H+ATPase function was supported by similar functional losses and uncoupling ratio between the two proton pump domains observed in vacuoles from a PFK-null strain, which was also unable to grow at alkaline pH. In contrast, the R-to-Q mutation dramatically reduced a-subunit production, abolishing H+ATPase function completely. Thus in the context of dRTA, stability and function of the metabolon composed of H+ATPase and glycolytic components can be compromised by either loss of required PFK-1 binding (G820R) or loss of pump protein (R807Q).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acidosis, Renal Tubular / metabolism
  • Acidosis, Renal Tubular / physiopathology*
  • Amino Acid Sequence
  • Circular Dichroism
  • Glycolysis / physiology
  • Humans
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Phosphofructokinase-1 / genetics
  • Phosphofructokinase-1 / metabolism*
  • Protein Subunits / genetics
  • Protein Subunits / metabolism
  • Proton-Translocating ATPases / genetics*
  • Proton-Translocating ATPases / metabolism*
  • Saccharomyces cerevisiae
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Surface Plasmon Resonance
  • Vacuolar Proton-Translocating ATPases

Substances

  • Protein Subunits
  • Saccharomyces cerevisiae Proteins
  • Phosphofructokinase-1
  • ATP6V0A4 protein, human
  • Vacuolar Proton-Translocating ATPases
  • Proton-Translocating ATPases