Figure 3

Structure of Form-I St AckA. (A) Tertiary structure of St AckA illustrating the N- (domain-I) and C-terminal (domain-II) domains of the enzyme. The core secondary structural elements (βββαβαβα) are shown in green (strands) and cyan (helices), while insertions of subdomains between secondary structural elements are highlighted in magenta (strands) and yellow (helices). Secondary structural elements of the core are numbered α_I1, α_I2… for α-helices, 3_I1, 3_I2… for 3₁₀ helices, β_I1, β_I2… for β-strands in domain-I and as α_II1, α_II2… for α-helices, 3_II1, 3_II2… for 3₁₀ helices, β_II1, β_II2… for β-strands in domain-II. Insertion domains are indexed similarly and numbered alphabetically. N- and C- termini of the subunit are also marked. (B) Topology diagram of St AckA indicating the ASKHA core fold and the location of the five conserved motifs. Arrows represent β-strands while cylinders represent helices, respectively. The coloring and secondary structure labeling scheme is similar to that of Figure 3A. (C) Dimeric structure of St AckA. The approximate size of a dimeric unit is 84 x 83 x 69 ų. A-subunit of the dimer is illustrated using the same colouring scheme to that of Figure 3A. Domain-I and -II of the B-subunit are shown in grey and brown, respectively. The dimer is mainly held by interactions between the C-terminal domains (domain-II) of the two subunits, while domain-I of each subunit protrudes out of the body of the dimeric enzyme. The 2-fold axis is highlighted by dotted line. Secondary structures corresponding to the core helices are labeled.