Ion pairs significantly stabilize coiled-coils in the absence of electrolyte.
We have used a synthetic coiled-coil peptide model system to address the long perplexing issue as to why coiled-coils are in general more stable at acidic pH than at neutral pH. Contrary to the above expectation, our results show that at low ionic strength (10 mM) the coiled-coil was much more stable at neutral pH than at acidic pH against both thermal and urea unfolding, indicating that the Lys(+)-Glu- ions pairs present around the coiled-coil interface at neutral pH contribute significantly to the stability of the coiled-coil. However, while the addition of NaCl had no significant effect on the coiled-coil stability at neutral pH, its stability at acidic pH increased dramatically. The cross-over point between the stability at acidic pH and neutral pH occurred at around 100 mM salt, above which the coiled-coil became more stable at acidic pH, in agreement with published results. Therefore, salt effect, rather than intrinsic property, such as carboxyl-carboxyl hydrogen bonding, causes this coiled-coil to become more stable at acidic pH. The preferential stabilizing effect of salt on the coiled-coil at acidic pH can be best explained in terms of the condensation of anions to the positively charged groups on the coiled-coil, the net density of which increases as glutamic acid residues become protonated in acidic pH.
Yu
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Department of Biophysics, Johns Hopkins University, Baltimore, MD 21218, USA.
Monera
O D
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Hodges
R S
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Privalov
P L
PL
D000595:Amino Acid Sequence; D002712:Chlorides / Q000737:chemistry; D002942:Circular Dichroism; D004573:Electrolytes; D018698:Glutamic Acid / Q000737:chemistry*; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007477:Ions; D008239:Lysine / Q000737:chemistry*; D008969:Molecular Sequence Data; D009994:Osmolar Concentration; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry*; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D012964:Sodium / Q000737:chemistry
D002712:Chlorides; D004573:Electrolytes; D007477:Ions; D010455:Peptides; D018698:Glutamic Acid; D012964:Sodium; D008239:Lysine