The cytoplasmic tail of the cation-independent mannose 6-phosphate receptor contains four binding sites for AP-1

The trafficking of the cation-independent mannose 6-phosphate receptor between the trans-Golgi network and endosomes requires binding of sorting determinants in the cytoplasmic tail of the receptor to adaptor protein complex-1 (AP-1). Using a GST pull-down binding assay, four binding motifs were identified in the cytoplasmic tail: a tyrosine-based motif ( ²⁶YSKV²⁹), an internal dileucine-based motif ( ³⁹ETEWLM⁴⁴), and two casein kinase 2 sites ( ⁸⁴DSEDE⁸⁸ and ¹⁵⁴DDSDED¹⁵⁹). The YSKV motif mediated the strongest interaction with AP-1 and the two CK2 motifs bound AP-1 only when they were phosphorylated. The COOH-terminal dileucines were not required for interaction with AP-1.