title: Dileucine signal-dependent and AP-1-independent targeting of a lysosomal glycoprotein in Trypanosoma brucei.
abstract: Sorting of trans-membrane proteins destined for the lysosome is achieved by selective inclusion into post-Golgi transport vesicles. In higher eukaryotes sorting may be mediated by a peptidic motif, principally acidic clusters and tyrosine- or dileucine-based cytoplasmic signals or by inclusion of mannose-6-phosphate (M6P) into the N-glycans of lysosomal proteins. In African trypanosomes a major lysosomal trans-membrane protein is CB-1/p67. The cytoplasmic domain of p67 lacks tyrosine and lysine, but does contain a canonical dileucine sequence embedded within an acidic region. AP-1, -3 and -4 adaptin complexes, which recognise tyrosine- and dileucine-sorting signals, are encoded by the trypanosome genome, but the genes for M6P-receptors or activities required to produce M6P are absent, suggesting that lysosomal delivery of p67 is most likely adaptin-mediated. By construction of p67 reporter constructs we show that the dileucine signal is necessary and sufficient for efficient lysosomal delivery of a trans-membrane protein in bloodstream stage trypanosomes. However, this targeting does not require AP-1, as knockdown of the trypanosome gamma-adaptin subunit by RNAi has no detectable effect on the location or maturation of p67. These data suggest that p67 is targeted to the lysosome by dileucine-dependent but AP-1-independent mechanisms.
authors.affiliation: The Molteno Building, Department of Pathology, Tennis Court Road, University of Cambridge, Cambridge CB2 1QP, UK.
authors.forename: Clare L
authors.initials: CL
authors.lastname: Allen
authors.forename: Dangjin
authors.initials: D
authors.lastname: Liao
authors.forename: Wei-Lian
authors.initials: WL
authors.lastname: Chung
authors.forename: Mark C
authors.initials: MC
authors.lastname: Field
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D019677:Artificial Gene Fusion; D017930:Genes, Reporter; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000235:genetics* / Q000502:physiology*; D021381:Protein Transport; D015800:Protozoan Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000235:genetics / Q000378:metabolism*
chemical_list: D006023:Glycoproteins; D021382:Protein Sorting Signals; D015800:Protozoan Proteins