Figure 4

Sequence conservation within the actin-binding region of the α-subunits. The sequence logos are based on 368 α-subunit sequences and illustrate the sequence conservation within the multiple sequence alignment of the α-subunits. Here, only the C-termini of the α-subunits are shown because most of the residues implicated in actin binding map to this region (For the representation of the entire α-subunits see Additional file1). For better orientation, the sequences of five representative α-subunits are shown: the three isoforms of chicken Cap1 for comparison because all previous crystal structures have been obtained from chicken Cap1α, the yeast Cap1 as one of the targets of mutagenesis experiments, and Dictyostelium Cap34 whose structure is presented here. Secondary structural elements as determined from the chicken CapZ crystal structure are drawn as yellow arrows (β-strands) and as red boxes (α-helices). Residues important for inter-heterodimer binding, V-1 binding, PIP₂-binding, and actin-binding are highlighted by orange, green, red, and purple stars, respectively. Numbering below the logos refers to positions in the multiple sequence alignment (The full-length multiple sequence alignment of the α-subunits is available as Additional File2).