Cooperative function and mutual stabilization of the half ATP-binding cassette transporters HAF-4 and HAF-9 in Caenorhabditis elegans

Caenorhabditis elegans HAF-4 and HAF-9 are half ABC transporters that are highly homologous to the human lysosomal peptide transporter TAPL (TAP-like; ABCB9). Previously, we reported that both HAF-4 and HAF-9 localize to the membrane of a subset of intestinal organelles, and are required for the formation of these organelles and other physiological aspects. Here, we report the genetic and physical interactions between HAF-4 and HAF-9. Overexpression of HAF-4 and HAF-9 did not rescue the intestinal organelle defect of the haf-9 and haf-4 deletion mutants, respectively, indicating that they cannot substitute for each other. Double haf-4 and haf-9 mutants do not exhibit more severe phenotypes than the single mutants, suggesting their cooperative function. Immunoprecipitation experiments demonstrated their physical interaction. These results suggest that HAF-4 and HAF-9 form a heterodimer. Furthermore, western blot analysis of the deletion mutants and RNAi knockdown experiments in GFP-tagged HAF-4 or HAF-9 transgenic worms suggest that HAF-4-HAF-9 heterodimer formation is required for their stabilization. These findings provide a clue on how ABC transporters adopt a stable, functional form.

Source: BJ Cell - March 5, 2013 Category: Biochemistry Authors: T Tanji, K Nishikori, H Shiraishi, M Maeda, A Ohashi-Kobayashi Tags: BJ Cell Source Type: research