The conclusions of the 2012 MIRG study were announced at the ABRF 2013 annual meeting in Palm Springs earlier this month.
In the study, a pair of unknown proteins, prepared and characterized by the ABRF, was sent out to multiple labs to determine affinity and stoichiometry of binding. In a single afternoon consisting of 2 CG-MALS runs, the Wyatt Calypso system correctly determined that one molecule of Protein Y (26.3 kDa) binds 2 molecules of Protein X (11.9 kDa), one with KD of 10 nM and the other with 14 µM. This analysis agreed perfectly with the extensive AUC and ITC measurements performed by ABRF prior to distributing the samples.
The CG-MALS measurement was the only solution-based measurement among the participating labs. The others used surface plasmon resonance (SPR) instruments which require immobilization of one of the binding partners. Only 4 of 13 SPR labs correctly measured and interpreted the data, typically taking 1-2 days even though the chip immobilization recipe and regeneration were provided by the organizers.
Interestingly, the affinities determined by SPR were significantly weaker than those found by any of the solution-based measurements (AUC, ITC, CG-MALS), indicating that, in this instance, immobilization modifies the interaction.