Pathways of disulfide formation

The normal pathway

We have described the pathway for the enzymatic catalysis of disulfide bond formation. We have shown that the oxidative power for protein folding originates with quinone reduction and revealed that disulfide bonds originate from oxygen in vivo.

Bader (1999) Oxidative protein folding is driven by the electron transport system. Cell 98: 217-227. (Pubmed) pdf_icon This paper was the subject of a News and Views in Nature 401:30-31 (1999) pdf_icon and was a focus of a minireview in Cell 96: 751-753 (1999) pdf_icon

An Engineered Pathway

Generally, evolution is thought to proceed by making slight alterations. In this paper we observed evolution making a big step. E. coli was put under a strong genetic selection, and the bacteria came up with a completely new answer to the problem of how to form disulfide bonds. We forced bacteria to use thioredoxin, normally a reductant, to make disulfide bonds instead. The thioredoxin variants we isolated had acquired an iron sulfur cluster and a new mechanism of catalyzing disulfide formation. Surprisingly the mutations were extremely simple, a single amino acid substitution generating an additional cysteine residue near thioredoxin’s active site. This shows that enzymes can acquire cofactors and transform their mechanism of action, via simple point mutations that could easily occur in nature. This dramatically illustrates the plasticity and potentially rapid nature of evolutionary change.

Masip et al (2004) An engineered pathway for the formation of disulfide bonds. Science 303: 1185-1189. (Pubmed) pdf_icon News story in Science Daily.