X-Message-Number: 31736
Date: Thu, 11 Jun 2009 00:02:03 -0700 (PDT)
From: 
Subject: TMAO and sulfate both look interesting

[Not many solutes can stabilize proteins at low temperatures.]

Biochemistry. 2008 Mar 18;47(11):3322-31. Epub 2008 Feb 23.

Singular efficacy of trimethylamine N-oxide to counter protein destabilization 
in ice.

  Strambini GB, Gonnelli M. Consiglio Nazionale delle Ricerche, Istituto di 
  Biofisica, 56124 Pisa, Italy.

  This study reports the first quantitative estimate of the thermodynamic 
  stability (Delta G degrees ) of a protein in low-temperature partly frozen 
  aqueous solutions in the presence of the protective osmolytes trimethylamine 
  N-oxide (TMAO), glycine betaine, and sarcosine. The method, based on 
  guanidinium chloride denaturation of the azurin mutant C112S from Pseudomonas 
  aeruginosa, distinguishes between the deleterious effects of subfreezing 
  temperatures from those due specifically to the formation of a solid ice 
  phase. The results point out that in the liquid state molar concentrations of 
  these osmolytes stabilize significantly the native fold and that their effect 
  is maintained on cooling to -15 degrees C. At this temperature, freezing of 
  the solution in the absence of any additive causes a progressive 
  destabilization of the protein, Delta G degrees decreasing up to 3-4 kcal/mol 
  as the fraction of liquid water in equilibrium with ice ( V L) is reduced to 
  less than 1%. The ability of the three osmolytes to prevent the decrease in 
  protein stability at small V L varies significantly among them, ranging from 
  the complete inertness of sarcosine to full protection by TMAO. The singular 
  effectiveness of TMAO among the osmolytes tested until now is maintained high 
  even at concentrations as low as 0.1 M when the additive stabilization of the 
  protein in the liquid state is negligible. In all cases the reduction in Delta
  G degrees caused by the solidification of water correlates with the decrease 
  in m-value entailing that protein-ice interactions generally conduct to 
  partial unfolding of the native state. It is proposed that the remarkable 
  effectiveness of TMAO to counter the ice perturbation is owed to binding of 
  the osmolyte to ice, thereby inhibiting protein adsorption to the solid phase.
  PMID: 18293933

J Phys Chem B. 2008 Aug 21;112(33):10255-63. Epub 2008 Jul 30.
Specific anions effects of on the stability of azurin in ice.

  Strambini GB, Gonnelli M. Istituto di Biofisica, Consiglio Nazionale delle 
  Ricerche, Pisa, Italy.

  This investigation represents a first attempt to gain a quantitative estimate 
  of the effects of the anions sulfate, citrate, acetate, chloride and 
  thiocyanate on the thermodynamic stability (DeltaG degrees) of a model 
  globular protein in ice at -15 degrees C. The method, based on guanidinium 
  chloride denaturation of the azurin mutant C112S from Pseudomonas aeruginosa, 
  distinguishes between the effects of cooling to subfreezing temperatures from 
  those induced specifically by the formation of a solid ice phase. The results 
  confirm that, both in liquid and frozen states, kosmotropes (sulfate, citrate 
  and acetate) increase significantly protein stability, relative to chloride, 
  whereas the chaotrope thiocyanate decreases it. Throughout, their stabilizing 
  efficacy was found to rank according to the Hofmeister series, 
  sulfate>citrate>acetate>chloride>thiocyanate, although the magnitude of 
  Delta(DeltaG degrees) exhibited a distinct sensitivity among the anions to low
  temperature and to ice formation. In the liquid state, lowering the 
  temperature from +20 to -15 degreesC weakens considerably the stabilizing 
  efficacy of the organic anions citrate and acetate. Among the anions sulfate 
  stands out as the only strong stabilizer at subfreezing temperatures while 
  SCN- becomes an even stronger denaturant. Freezing of the solution in the 
  presence the "neutral" salt NaCl destabilizes the protein, DeltaG degrees 
  progressively decreasing up to 3-4 kcal/mol as the fraction of liquid water in
  equilibrium with ice (VL) is reduced to less than 1%. Kosmotropes do 
  attenuate the decrease in protein stability in ice although in the case of 
  citrate and acetate, their efficacy diminishes sharply as the liquid fraction 
  shrinks to below 2.7%. On the contrary, sulfate is remarkable for it maintains
  constantly high the stability of azurin in liquid and frozen solutions, down 
  to the smallest VL (0.5%) examined. Throughout, the reduction in DeltaG 
  degrees caused by the solidification of water correlates with the decrease in 
  the denaturant m value, an indirect indication that protein-ice interactions 
  generally lead to partial unfolding of the native state. It is proposed that 
  binding of the kosmotropes to the ice interface may inhibit protein adsorption
  to the solid phase and thereby counter the ice perturbation.
PMID: 18665632

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