AVP2, a Sequence-Divergent, K+-Insensitive H+-Translocating Inorganic Pyrophosphatase from Arabidopsis

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Abstract
Plant vacuolar H+-translocating inorganic pyrophosphatases (V-PPases; EC 3.6.1.1) have been considered to constitute a family of functionally and structurally monotonous intrinsic membrane proteins. Typified by AVP1 (V. Sarafian, Y. Kim, R.J. Poole, P.A. Rea [1992] Proc Natl Acad Sci USA 89: 1775–1779) from Arabidopsis, all characterized plant V-PPases share greater than 84% sequence identity and catalyze K+-stimulated H+ translocation. Here we describe the molecular and biochemical characterization of AVP2 (accession no. AF182813), a sequence-divergent (36% identical) K+-insensitive, Ca2+-hypersensitive V-PPase active in both inorganic pyrophosphate hydrolysis and H+ translocation. The differences between AVP2 and AVP1 provide the first indication that plant V-PPases from the same organism fall into two distinct categories. Phylogenetic analyses of these and other V-PPase sequences extend this principle by showing that AVP2, rather than being an isoform of AVP1, is but one representative of a novel category of AVP2-like (type II) V-PPases that coexist with AVP1-like (type I) V-PPases not only in plants, but also in apicomplexan protists such as the malarial parasite Plasmodium falciparum.

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