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The sarcosine effect on protein stability: A case of nonadditivity?
Author(s) -
IbarraMolero Beatriz,
Del Pino Isabel M. Plaza,
Souhail Badredine,
Hammou Hassan O.,
SanchezRuiz Jose M.
Publication year - 2000
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.9.4.820
Subject(s) - sarcosine , chemistry , lysozyme , accessible surface area , native state , crystallography , osmolyte , equilibrium unfolding , protein folding , additive function , gibbs free energy , enthalpy , thermodynamics , circular dichroism , amino acid , computational chemistry , glycine , physics , biochemistry , mathematical analysis , mathematics
We have used differential scanning calorimetry to determine the effect of low concentrations ( C = 0–2 M) of the osmolyte sarcosine on the Gibbs energy changes (δ G ) for the unfolding of hen‐egg‐white lysozyme, ribonuclease A, and ubiq‐uitin, under the same buffer and pH conditions. We have also computed this effect on the basis of the additivity assumption and using published values of the transfer Gibbs energies for the amino acid side chains and the peptide backbone unit. The values thus predicted for the slope ∂ΔL G /∂ C agree with the experimental ones, but only if the unfolded state is assumed to be compact (that is, if the accessibility to solvent of the unfolded state is modeled using segments excised from native structures). The additivity‐based calculations predict similar ∂ΔL G /∂ C values for the three proteins studied. We point out that, to the extent that this approximate constancy of ∂ΔL G /∂ C holds, osmolyte‐induced increases in denaturation temperature will be larger for proteins with low unfolding enthalpy (small proteins that bury a large proportion of apolar surface). The experimental results reported here are consistent with this hypothesis.