Two Distantly Spaced Basic Patches in the Flexible Domain of Huntingtin-Interacting Protein 1 (HIP1) Are Essential for the Binding of Clathrin Light Chain

Figure 1

Structural features of the HIP1 clathrin light chain-binding site. Two distantly separated basic amino acids in the opened region of HIP1 mediate the binding of clathrin light chain. The assembled model was generated using PDB files 2NO2 [8] and 2QA7 [9]. For the sake of clarity, we only show a portion of the second HIP1 helix (dark grey) that stops before Y468. The yellow bar marks the position of the solvent exposed hydrophobic S3 path [8]. The new data in Figure 3 indicate that K474 is a strong determinant for binding and imply that S3 path begins before the DLL₄₈₆R₄₈₇KN region. The N- and C-termini of the HIP1 crystal structure are labeled N and C. The numbers 1–3 along the yellow bar mark the position of amino acids that control the binding of clathrin light chain (position 1: K474; position 2: L486 and R487 reported by the McPherson group [7]; and position 3: K494). K474 and K494 are ~50 Å apart. R500, R508 or K511 (see arrow) do not participate in binding and therefore define the boundary of the light chain-binding site. The HIP1 468-530 subfragment used in the CD studies in Figure 2 spans across an opened region of the HIP1 coiled coil in our 2NO2 and 2QA7 crystal structures. The HIP1 model was created using PyMol (http://www.pymol.org).