Fig. 4. A continuous channel between the ADH and AlDH active sites.

a A conserved channel crosses the monofunctional propionaldehyde dehydrogenase from R. palustris (left panels). This channel is conserved in the AlDH domain in AdhE (right panel). Top, cut-out slice through the AlDH domain of the bottom, surface representation of the AlDH domain showing the substrate entrance/exit channel (opposite of the NAD-binding channel). b A conserved channel crosses the monofunctional lactaldehyde : 1,2-propanediol oxidoreductase from E. coli (left panels). This channel is conserved in the ADH domain in AdhE (right panel). Top, cut-out slice through the ADH domain of the bottom, surface representation of the ADH domain showing the substrate entrance/exit channel (opposite of the NAD-binding channel). c Surface representation of ADH_α (in light blue) and AlDH_β (in blue). The loops 2 and 3 from ADH_α are colored in red. d A channel connects directly the active sites of ADH_α (in light blue) and AlDH_β (in blue). The domains are represented as transparent surfaces and ribbons with the same color code than above. A surface representation of channel is colored in yellow. Surface representations of NAD⁺ molecules bound to ADH and AlDH domains are colored in green.