Anion binding to a protein–protein complex lacks dependence on net charge

Abstract

The binding of anions to proteins occurs in numerous physiological and metabolic processes. In an effort to understand the factors important in these interactions, we have studied the weak binding of phosphate and sulfate to a protein-protein complex using isothermal titration calorimetry. To our knowledge, this is the first system in which the thermodynamics of anion binding have been determined calorimetrically. By studying both phosphate and sulfate binding and using a range of pH values, the charge on the anion was varied from ∼ −1 to −2. Surprisingly, no dependence of the binding energetics on the charge of the anion was observed. This result indicates that charge-charge interactions are not the dominant factor in binding and suggests the importance of hydrogen bonding in specifically recognizing and coordinating anions.

The determinants of carboxyl pKa values in turkey ovomucoid third domain

“…It is interesting that an ionic strength dependence of 0.8 units has been observed40 for the pK a of Glu19, which is traditionally ascribed to screening of long‐range interactions. Given that hydrogen bonding appears to be the prime determinant of this pK a , it is possible that an ionic strength increase may alter the hydrogen‐bonding pattern around the residue, perhaps by ion binding at a specific site close to the ionizable residue 34, 82. The ionic strength dependence of the pK a values of Asp7 and Asp27, for which we also predict that hydrogen bonding is the main determinant, varied by 0.0–0.6 and 0.4–0.5 units, respectively, depending on which proton resonance was used to determine the titration curve 40…”

The connection between metal ion affinity and ligand affinity in integrin I domains

“…where R is the gas constant at 8.315 J•K −1 •mol −1 and T is the temperature set at 299 K (26°C) in all experiments. Non-linear least square fitting of Equation (1) to the experimental data was accomplished as described [19].…”

Use of additives to enhance the properties of cottonseed protein as wood adhesives

“…In contrast, the hot water resistance of soy protein isolate seemed to be negatively impacted by these additives, with arginine showing the biggest impact with all the adhesive joints failing during the heat soak treatment. Such interactions are believed to facilitate protein denaturation and destabilization, although the mechanisms responsible are debated [32,33]. In addition, arginine is known to decrease heatinduced protein aggregation [35][36], making the protein more easily denatured at temperatures above 80ºC [37].…”