FIGURE 5.
Molecules of glycerol and PEG bound in pockets within the two major actin-binding sites of fascin. A, surface representation of the actin-binding site in β-trefoil-1 colored by residue conservation (left) and an enlarged view (right) showing molecules of PEG bound in the cleft formed at the interface between β-trefoil domains 1 and 4 (see also supplemental Movie 1). Residue conservation decreases from blue to red as indicated by the bar at the bottom of the figure. Note that the actin-binding site in β-trefoil-1 includes the MARCKS-related sequence (fascin residues 29–43; indicated by a mesh surface) and residue Ser39 (labeled), which have been implicated in actin binding (7, 8). An alignment of the sequences of human fascin (UniProt accession number Q16658) and MARCKS (UniProt accession number P29966) is shown for this region (identity, dark blue; conservation, different shades of cyan). B, surface representation of the actin-binding site in β-trefoil-3 (left) and an enlarged view (right) of a molecule of glycerol bound in a pocket formed at the interface between β-trefoil domains 2, 3, and 4. The two actin-binding sites are related by pseudo-2-fold symmetry as indicated. Also shown are some of the amino acids that form the binding pockets for the molecules of PEG and glycerol as well as the 2Fo−Fc electron density map contoured at 1.0 σ around these molecules. Shown alongside are small domain-colored diagrams of the fascin structure in the same orientation.