Comparison of Form-I and -II St AckA. (A) Plot of residual distance between sequentially equivalent Cα atoms against residue number obtained after pairwise superposition of A-subunit of Form-I and A- and B-subunits of Form-II StAckA. Labeling scheme – e.g. IIA-IIB corresponds to distances between equivalent Cα atoms after superposition of Form-II B-subunit on Form-II A-subunit. The insets show the variable segment (residues 230–300) Cα atom distances highlighting large conformational differences (corresponding to ~18% of the total length of the enzyme). Region corresponding to residues 251–260 (refer Additional file 1: Figure S1 for fit of the electron density) are marked by vertical dotted lines. (B) Structural superposition of the A-subunit of Form-I (salmon-red) with A- (yellow) and B- (cyan) subunits of the Form-II StAckA highlighting the structural differences of the variable segment. Secondary structures corresponding to the core helices and variable segments (labels corresponding to I-A, II-A and II-B subunits are enclosed using ○, □ and Δ shapes, respectively) are labeled. Met230 and Lys300 occur at the ends of the variable segment. (C) Form-II StAckA dimer highlighting regions of variable segment (A-subunit, yellow except for the variable segment shown in bright-orange; B-subunit, cyan with variable segment highlighted in blue). Citrate (pink, CIT-501) bound at the dimeric interface is shown in ball and stick representation. Secondary structures corresponding to the variable segments of each subunit are labeled.
Chittori et al. BMC Structural Biology 2012 12:24 doi:10.1186/1472-6807-12-24