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A structural explanation for the binding of endocytic dileucine motifs by the AP2 complex

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Most transmembrane proteins are selected as transport-vesicle cargo through the recognition of short, linear amino-acid motifs in their cytoplasmic portions by vesicle coat proteins. For clathrin-coated vesicles, the motifs are recognized by clathrin adaptors. The AP2 adaptor complex (subunits α, β2, μ2 and σ2) recognizes both major endocytic motifs: YxxΦ motifs1 (where Φ can be F, I, L, M or V) and [ED]xxxL[LI] acidic dileucine motifs. Here we describe the binding of AP2 to the endocytic dileucine motif from CD4 (ref. 2). The major recognition events are the two leucine residues binding in hydrophobic pockets on σ2. The hydrophilic residue four residues upstream from the first leucine sits on a positively charged patch made from residues on the σ2 and α subunits. Mutations in key residues inhibit the binding of AP2 to ‘acidic dileucine’ motifs displayed in liposomes containing phosphatidylinositol-4,5-bisphosphate, but do not affect binding to YxxΦ motifs through μ2. In the ‘inactive’ AP2 core structure3 both motif-binding sites are blocked by different parts of the β2 subunit. To allow a dileucine motif to bind, the β2 amino terminus is displaced and becomes disordered; however, in this structure the YxxΦ-binding site on μ2 remains blocked.

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Figure 1: Structure of the AP2 adaptor core in complex with the dileucine peptide from CD4.
Figure 2: Details of binding of the CD4 dileucine signal by the σ2 and α subunits of AP2.
Figure 3: Confirmation of location and conservation among different σ subunits of the dileucine-motif-binding site.
Figure 4: A conformational change in AP2 is required for dileucine peptide binding.

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Protein Data Bank

Data deposits

Atomic coordinates and structure factors have been deposited with the Protein Data Bank under accession numbers 2jkr for the Q peptide complex and 2jkt for the E peptide complex, respectively.

Change history

  • 18 December 2008

    The AOP version of this paper carried an erroneous affiliation for D.J.O. This was corrected on 18 December 2008.


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We thank the protein crystallography beamline staff at Diamond, especially E. Duke, K. McAuley and R. Flaig, for their support and assistance. D.J.O., B.T.K. and S.E.M. are funded by a Wellcome Trust Senior Research Fellowship to D.J.O. S.H. and K.S. are supported by grants from the Deutsche Forschungsgemeinschaft (SFB635 and SFB670).

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Correspondence to David J. Owen.

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This file contains Supplementary Figures S1-S9 with Legends and Supplementary Tables S1-S3. (PDF 2219 kb)

Supplementary Movie 1

Supplementary Movie 1 shows animation of the conformational change between the IP6-liganded, inactive conformation (2vgl) and the acidic dileucine motif bound conformations of the AP2 core. The two structures were superimposed on the σ2 subunit. Residues Y6 and F7 are highlighted in the closed structure (green balls) and the dileucine peptide is shown in gold. The two structures are alternated first in a "front" view, then from a "back" view, rotated by 180° (MOV 2055 kb)

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Kelly, B., McCoy, A., Späte, K. et al. A structural explanation for the binding of endocytic dileucine motifs by the AP2 complex. Nature 456, 976–979 (2008).

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