Figure 3.

Native mass spectrum for GroEL. (A) Mass spectrum of GroEL obtained using low source potential nESI contains abundance signals for intact 14-mer complex centered at 74⁺. The inset in (A) contains a narrow m/z range that illustrates the high resolution obtained for the intact 14-mer complex shown and the crystal structure of GroEL (PDB 1SS8). (B) In-source dissociation (ISD) mass spectrum of GroEL contains strong signals for unfolded and native-like monomer ions (charge states 20⁺ and 32⁺, respectively) as well as di- and tri-mer ions centered at 25⁺, and 29⁺, respectively. The measured MWs for each of the GroEL species are reported in the boxes. Note that the measured mass for the CSD labeled with an * (assigned as 51⁺ ions with MW of 465.9 kDa) does not agree with any known ions derived from GroEL (see text). It is possible that this species could be an 8-mer of GroEL, as an intact 7-mer with a monomer trapped inside the cavity along with water, salts, and other small molecules.