UCLA

Electrospray ionization (ESI) coupled to gas-phase electrophoretic mobility molecular analysis (GEMMA) is a soft ionization technique capable of characterizing large protein complexes. Particles are separated by their mobility in air and their size is determined as electrophoretic mobility diameter (EMD). This data can be converted to molecular weight information by modeling the particles as spheres and taking into account their average density. Here we adapt ESI-GEMMA towards the study of 1.5 MDa E2 protein cages and 9 MDa vault nanoparticles. Recombinant vaults with N- and C- terminal tags of varying mass were used as standards to calibrate the GEMMA data specifically for the study of vault complexes. We used this improved calibration to evaluate the composition and integrity of different vault preparations. Additionally, we quantified the capacity of vaults to be loaded with protein drugs and monitored the stability of these formulations over time.