An approach for improving the resolution and accessibility of a mass spectrometry technique to obtain important structural information about intact multiprotein complexes is published online this week in Nature Methods.

Structural details about large multiprotein complexes, including what molecules can bind to them and how the complexes assemble, can be measured using mass spectrometry methods that allow for the detection of high-molecular-weight ions. To date, this technique has required the use of specially modified mass spectrometers and has been limited to a few expert labs.

Albert Heck and colleagues describe modifications to an Orbitrap mass spectrometer-a popular type of instrument that is widely used in high-throughput protein profiling-that now allow it to measure intact multiprotein complexes with molecular weights of up to 1,000 kDa. The resolution of their approach was adequately high to distinguish the binding of individual ATP or ADP molecules to the bacterial chaperonin complex GroEL, which to date has not been possible with intact mass spectrometry methods. The method should also allow applications such as the sensitive detection of post-translational modifications on multiprotein complexes.