Hydrogen Bonding and Noncovalent Electric Field Effects in the Photoconversion of a Phytochrome.

A profound understanding of protein structure and mechanism requires dedicated experimental and theoretical tools to elucidate electrostatic and hydrogen bonding interactions in proteins. In this work, we employed an approach to disentangle noncovalent and hydrogen-bonding electric field changes during the reaction cascade of a multidomain protein, i.e.

On the Role of a Conserved Tryptophan in the Chromophore Pocket of Cyanobacteriochrome.

The cyanobacteriochrome Slr1393 can be photoconverted between a red (Pr) and green absorbing form (Pg). The recently determined crystal structures of both states suggest a major movement of Trp496 from a stacking interaction with ring D of the phycocyanobilin (PCB) chromophore in Pr to a position outside the chromophore pocket in Pg. Here, we investigated the role of this amino acid during photoconversion in solution using engineered protein variants in which Trp496 was substituted by natural and non-natural amino acids.