Fig. 5: Structural comparison of photocobilins with CarH⁴ and BV binding protein^20,21.

Overall structure of the dark states of the AbPCob (a) and SasPcob (b) protein, and the light state of SasPcob (c). The Rossmann fold region is coloured blue, four-helix-bundle region in green and BV binding region in red. The AdoCbl and BV molecules are shown as pink and yellow spheres. d Structural alignment of SasPcob, AbPcob and CarH proteins (5C8A). The B₁₂ binding region is shown as green (SasPcob), cyan (AbPcob), and magenta (CarH) ribbons. The BV binding domain is shown as yellow (SasPcob) and blue (AbPcob) ribbons. e Sequence alignment of SasPcob, AbPcob and CarH proteins. The alignment result is coloured according to sequence identity by MView⁵⁶. The residues in the red box are the key residues at the dimer interface. f Structural alignment of BV binding domain of SasPcob (green) and AbPcob (cyan). The BV molecule is shown as red sticks. g Structural alignment of BV binding domains of SasPcob (green) and AbPcob (cyan) with phycobilisome proteins 1B33²⁰ (yellow) and 3MWN²¹ (magenta). BV molecules and key residues involved with BV binding are shown as red (SasPcob), cyan (AbPcob), yellow (3MWN), light-blue (1B33) sticks. h Comparison of the BV chromophore in the binding pocket. Cys residues bonding with BV (Top, 1B33 and 3WMN), and residues at same position (bottom, SasPcob and AbPcob) are shown as sticks. The same colour scheme is used as in (g). The BV is shown in red for SasPcob, yellow for 1B33¹¹ and blue for 3MWN¹². i Sequence alignment of photocobilins with 3MWN and 1B33. The residues in the red box forms the BV binding motif.