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Abstract
Chaperonins are nanomachines that harness ATP hydrolysis to power and catalyze protein folding, chemical action that is directly linked to the maintenance of cell function through protein folding/refolding and assembly. GroEL and the GroEL-GroES complex are archetypal examples of such protein folding machines. Here, variable-temperature-electrospray ionization (vT-ESI) native mass spectrometry is used to delineate the effects of solution temperature and ATP concentrations on the stabilities of GroEL and GroEL/GroES complexes. The results show clear evidences for de-stabilization of both GroEL14 and GroES7 at temperatures of 50 oC and 45 oC, respectively, substantially below the pre-viously reported melting temperature (Tm ~ 70 oC). This destabilization is accompanied by temperature-dependent reaction products that have previously unreported stoichiometries, viz. GroEL14-GroESx-ATPy, where x = 1, 2, 8 and y = 0, 1, 2, that are also dependent on Mg2+ and ATP concentrations. Variable-temperature native mass spectrometry re-veals new insights about the stability of GroEL in response to several environmental effects: (i) temperature-dependent ATP binding to GroEL (ii) effects of temperature as well as Mg2+ and ATP concentrations on the stoichiome-try of the GroEL-GroES complex, with Mg2+ showing greater effects compared to ATP; and, (iii) a change in the temper-ature-dependent stoichiometries of the GroEL-GroES complex (GroEL14-GroES7 vs GroEL14-GroES8) between 24 to 56 oC. The similarities between results obtained using native MS and cryo-EM (Clare et al., An expanded protein folding cage in the GroEL-gp31 complex. J. Mol. Biol. 2006, 358, 905-11; Ranson et al., Allosteric signaling of ATP hydrolysis in GroEL–GroES complexes. Nat. Struct. Mol. Biol. 2006, 13, 147-152.) underscores the utility of native MS for investiga-tions of molecular machines as well as identification of key intermediates involved in the chaperone-assisted protein folding cycle.
