A blue fluorescent protein has an added extra that makes it a useful tool for biophysical studies, says a team of US researchers.

Andreas Bommarius, from the Georgia Institute of Technology in Atlanta, and colleagues, investigated the natural function of a fluorescent protein from the marine bacterium Vibrio vulnificus. 

The fluorescent protein belongs to a common and diverse family of molecules called the short-chain dehydrogenase/reductase family. When it was isolated in 2001, it was the first of this family to show fluorescence, albeit weak. But it was different from previously found fluorescent proteins. It folds into a different structure and magnifies its fluorescence by binding to NADPH, a molecule involved in oxidation/reduction reactions in cells, said Bommarius. 

The team found that the V. vulnificus protein could be used to reduce a series of aldehydes and ketones. Most of the fluorescent proteins that have been identified to date have no function beyond their fluorescence.

'A protein with both fluorescence and catalytic activity is a useful tool for our work on enzymes in organic-water mixtures,' said Bommarius. Fluorescent proteins can be used in protein biophysics to track the folding status of proteins. With this example, 'we can effectively see the difference between a properly folded protein that is no longer active because of the solvent (still fluorescent, but loses activity) and a misfolded protein (no longer fluorescent or active),' he said. 

Bommarius hopes to understand why the protein became fluorescent, by creating and analysing fluorescent variants of a non-fluorescent enzyme. Future challenges include investigating whether fluorescence and activity are linked, are independent, or even mutually exclusive. Bommarius also wants to find ways of enhancing both fluorescence and activity.

Elinor Richards