Stabilization of proteins by guanidination.

Area of Science:

• Biochemistry
• Protein Chemistry
• Structural Biology

Background:

• Pronase endopeptidases show resistance to denaturation in high urea or guanidine hydrochloride concentrations.
• Proteins with low or no lysine residues exhibit greater stability.
• Lysine side chains may be less stable than arginine in aqueous environments due to solvation dynamics.

Purpose of the Study:

• To investigate the hypothesis that arginine residues contribute to protein stability more than lysine residues.
• To determine if converting lysine to homoarginine affects protein stability.

Main Methods:

• Guanidination of seven globular proteins: bovine carbonic anhydrase, chymotrypsinogen, alpha-lactalbumin, serum albumin, ribonuclease, hen egg lysozyme, and horse heart cytochrome c.
• Conversion of lysine residues to homoarginine (90-99% efficiency).
• Tritium-hydrogen isotope exchange to assess protein stability.

Main Results:

• All tested proteins, except lysozyme, showed reduced hydrogen isotope out-exchange after guanidination, indicating increased stability.
• Lysozyme, which has a high arginine to lysine ratio naturally, did not show significant changes.
• The conversion of lysine to homoarginine generally enhanced protein stability.

Conclusions:

• A high ratio of arginine to lysine residues contributes to enhanced protein stability.
• Arginine residues may confer greater structural integrity to proteins compared to lysine residues.
• Modifying lysine residues to homoarginine can increase protein resistance to denaturation.