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Multiple equilibria of the Escherichia coli chaperonin GroES revealed by mass spectrometry
Author(s) -
Donald Lynda J.,
Stokell David J.,
Holliday Neil J.,
Ens Werner,
Standing Kenneth G.,
Duckworth Harry W.
Publication year - 2005
Publication title -
protein science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.353
H-Index - 175
eISSN - 1469-896X
pISSN - 0961-8368
DOI - 10.1110/ps.041164305
Subject(s) - random hexamer , dimer , monomer , chemistry , trimer , equilibrium constant , groes , mass spectrometry , oligomer , chaperonin , escherichia coli , crystallography , protein folding , groel , organic chemistry , chromatography , biochemistry , polymer , gene
Nanospray time‐of‐flight mass spectrometry has been used to study the assembly of the heptamer of the Escherichia coli cochaperonin protein GroES, a system previously described as a monomer–heptamer equilibrium. In addition to the monomers and heptamers, we have found measurable amounts of dimers and hexamers, the presence of which suggests the following mechanism for heptamer assembly: 2 Monomers ↔ Dimer; 3 Dimers ↔ Hexamer; Hexamer + Monomer ↔ Heptamer. Equilibrium constants for each of these steps, and an overall constant for the Monomer ↔ Heptamer equilibrium, have been estimated from the data. These constants imply a standard free‐energy change, ΔG 0 , of about 9 kcal/mol for each contact surface formed between GroES subunits, except for the addition of the last subunit, where ΔG 0 = 6 kcal/mol. This lower value probably reflects the loss of entropy when the heptamer ring is formed. These experiments illustrate the advantages of electrospray mass spectrometry as a method of measuring all components of a multiple equilibrium system.