Traffic. 2012 Jan 30. doi: 10.1111/j.1600-0854.2012.01335.x. [Epub ahead of print]
Apicoplast targeting of a T. gondii transmembrane protein requires a cytosolic tyrosine-based motif.
Derocher AE, Karnataki A, Vaney P, Parsons M.
Seattle Biomedical Research Institute, 307 Westlake Ave N, Seattle Washington 98109-5219 University of Washington, Department of Global Health, Seattle Washington 98195-5065.
Toxoplasma gondii, like most apicomplexan parasites, possesses an essential relict chloroplast, the apicoplast. Several apicoplast membrane proteins lack the bipartite targeting sequences of luminal proteins. Vesicles bearing these membrane proteins are detected during apicoplast enlargement, but the means of cargo selection remains obscure. We used a combination of deletion mutagenesis, point mutations, and protein chimeras to identify a short motif prior to the first transmembrane domain of the T. gondii apicoplast phosphate transporter 1 (APT1) that is necessary for apicoplast trafficking. Tyrosine 16 was essential for proper localization; any substitution resulted in misdirection of APT1 to the Golgi body. Glycine 17 was also important, with significant Golgi body accumulation in the alanine mutant. Separation of at least eight amino acids from the transmembrane domain was required for full motif function. Similarly placed YG motifs are present in apicomplexan APT1 orthologues and the corresponding N-terminal domain from Plasmodium vivax was able to route T. gondii APT1 to the apicoplast. Differential permeabilization demonstrated that both the N- and C- termini of APT1 are exposed to the cytosol. We propose that this YG motif facilitates APT1 trafficking via interactions that occur on the cytosolic face of nascent vesicles destined for the apicoplast.
© 2012 John Wiley & Sons A/S.
PMID: 22288938 [PubMed - as supplied by publisher]