Fig. 2.

Architectural distortions and structural comparisons between precyclization and postcyclization states. (a) Superposition of R96A structures, emphasizing large conformational change for Y66 but otherwise small Cα differences between precyclization (A in yellow, B in blue) and postcyclization (green) states. (b) Central helix for three R96A structures displayed with the surface of the R96A mature structure, emphasizing helical bend. (c) Structural overlay of R96A precyclization intermediates A (yellow) and B (blue) with the mature R96A (green) structure, showing large main-chain movements in forming the chromophore. Modeled R96 (purple) indicates steric interactions with the Y66 side-chain position of the precyclization intermediate structure. (d) Superposition of the Gly-Gly-Gly structures before (blue, anaerobic) and after (green, aerobic) peptide cyclization shows functional group interactions between the R96, E222, and T62 carbonyl oxygen atoms and the chromophore residues. (e) Schematic of distortions in main-chain hydrogen-bonding interactions for the WT, Gly-Gly-Gly precyclization, and postcyclization structures (Left) displayed in comparison to a canonical α-helix (Right). Solid lines between main-chain atoms indicate presence of a hydrogen bond. a–d are illustrated with avs (45).