Guanidination, protein stability

A protein goes through heat denaturation when the temperature is raised. The melting temperature (i.e., the temperature at which half of the proteins in solution are unfolded) increases when protein stabilizers—such as polyols, sugars, and amino-acid derivatives—are present (Timasheff 2002b). Protein stabilizers are used in cells and in laboratories to protect proteins from heat denaturation. T, on the other hand, is reduced when denaturants—such as urea and guanidine hydrochloride—are present in the solution (Timasheff 2002b). Cosolvents can thus enhance or prevent thermal denaturation. 

Most physical properties of a protein change substantially when it unfolds. Consequently, many techniques can be used to follow unfolding those used most often are ultraviolet difference spectroscopy, circular dichroism, optical rotation, fluorescence, and NMR spectroscopies. One of the most popular methods of estimating protein stability is based on monitoring urea and guanidine hydrochloride denaturation curves of the protein. ... 

Guanidine forms salts with such relatively weak acids as nitromethane, phthalimide, phenol and carbonic acid [20], Interactions between carboxylate anions of proteins and added guanidinium ion are thought [19, 56] to be weaker than the interactions with ammonium ions the role of guanidinium-carboxylate interactions in stabilizing natural protein conformations has been discussed [36c]. A few reports of metal complex formation by guanidines [57-60], and aminoguanidines [61] have appeared. 

The guanidine group is a common structural feature in Nature, primarily due to its ability to stabilize the three-dimensional structure of proteins in enzymes through binding with anionic substrates. Roush and Walts (274) prepared the... 

On the basis of the equilibrium unfolding curves of authentic and recombinant a-lactalbumin, the recombinant protein is remarkably less stable than the authentic one (Fig. 2.2) [22]. The transition midpoints were 3.2 and 2.7 M guanidine hydrochloride (GdnHCl) for the authentic and recombinant proteins, respectively and the difference in the stabilization free energy AAGnu,... 

Conformationally rigid cavitands III have been used for the synthesis of four-helix bundle caviteins 29,60,61 which are de novo proteins composed of cavitands and proteins (Figure 4). The proximity of four a-helical peptides significantly stabilizes their native-like structure, which was proved by denaturation experiments with guanidine hydrochloride.62... 

Methods presently employed for obtaining correctly refolded proteins from inclusion body preparations are often all-or-none propositions. They typically consist of denaturant solubilization, in urea or guanidine, followed by dilution or dialysis (2). Recovery of native activity or structure may be aided by using additives (enzyme inhibitors, co-factors, oxidation-reduction couples, etc.), which act to stabilize the native-state protein conformation. However, because such efforts are time-consuming and tedious, systematic examinations of solution conditions for protein folding/unfolding are rarely performed. 

The conformational stabilities of HI and Pal-HI have been compared by studying the respective guanidine-HCl induced denaturation profiles. Experiments were conducted utilizing a concentration of 0.1 mg/mL protein in pH... 

Kim, K.-S. Woodward, C. (1993). Protein internal flexibility and global stability Effect of urea on hydrogen exchange rates of bovine pancreatic trypsin inhibitor. Biochemistry 32,9609-9613. Kuwajima, K., Nitta, K., Yoneyama, M. Sugai, S. (1976). Three-state denaturation of o-lactalbumin by guanidine hydrochloride. J. Mol. Biol. 106, 359-373. 

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