Structure of catalytically competent intein caught in a redox trap with functional and evolutionary implications.

Here we describe self-splicing proteins, called inteins, that function as redox-responsive switches in bacteria. Redox regulation was achieved by engineering a disulfide bond between the intein's catalytic cysteine and a cysteine in the flanking 'extein' sequence. This interaction was validated by an X-ray structure, which includes a transient splice junction. A natural analog of the designed system was identified in Pyrococcus abyssi, suggesting an unprecedented form of adaptive, post-translational regulation.