By studying molecular mechanisms of human disease-causing missense mutations within <i>a</i> subunit isoforms, we may identify domains critical for V-ATPase targeting, activity and/or regulation. cDNA-encoded FLAG-tagged human wildtype ATP6V0A2 (<i>a</i>2) and ATP6V0A4 (<i>a</i>4) subunits and their mutants, <i>a</i>2<sup>P405L</sup> (causing cutis laxa), and <i>a</i>4<sup>R449H</sup> and <i>a</i>4<sup>G820R</sup> (causing renal tubular acidosis, dRTA), were transiently expressed in HEK 293 cells.