These protein fragments are separated according to type by liquid chromatography, and a mass spectrometer then "weighs" each fragment type to see whether it has picked up oxygen atoms.
"Detecting an extra oxygen is child's play for a modern mass spectrometer," says Gross. "Most instruments can even detect an extra proton, with is one-sixteenth the mass of an oxygen atom."
"In the same instrument, on the fly, we break apart the protein fragments and again 'weigh' the bits to see which one still carries the oxygen atom. This lets us deduce the oxygen's location on the original fragment."
By following barstar to its first intermediate state, or way station enroute to its native state, the scientists demonstrated that the new technique can follow folding and unfolding on a submillisecond time scale.
'Massive amounts of detail'
Gross is the first to say that this proof-of-principle experiment stands at the end of a long line of elegant experiments of a similar type, called pump-probe experiments.
Other techniques probe the change in protein structure by monitoring the absorption or emission of light--or a similar physical effect. They can provide only global information, such as the rate constant of a folding reaction.
"Because we use a chemical rather than a physical probe, we can see what's going on in much greater detail," says Gross. "We can say which part of the structure closes first, which second, and so on."
The new technique caught the attention of protein scientist Martin Gruebele of the University of Illinois, who spotlighted it in the Dec. 2, 2010, issue of the journal Nature.
It "could provide truly massive amounts of detail about fast protein
|Contact: Diana Lutz|
Washington University in St. Louis