Interrogating the Osmotic Pressure of Self-Crowded Bovine Serum Albumin Solutions: Implications of Specific Monovalent Anion Effects Relative to the Hofmeister Series

Abstract

The free-solvent-based (FSB) model and osmotic pressure were used to probe the ion binding and protein hydration for self-crowded bovine serum albumin in 0.15 M NaF, NaCl, NaI, and NaSCN solutions. All experiments were conducted with solutions at pH 7.4. The regressed results of the FSB model behavior to the measured osmotic pressure were excellent, albeit, the osmotic pressure data for NaSCN were noisy. The resulting ion binding and hydration were realistic values and the covariance of the two parameters was exceptionally low, providing substantial credibility to the FSB model. The results showed that the kosmotropic F and neutral Cl solutions generated significantly higher ion binding and protein hydration than the chaotropic solutions of I and SCN. Further, the ionic strength ratio and resulting hydration implied that the chaotropic solutions had substantially higher aggregation than the other salts investigated. Overall, the FSB model provides an additional, complementary tool to contribute to the analysis of crowded protein solutions relative to anions in the Hofmeister series as it can interrogate crowded solutions directly; something that is not possible with many measurement techniques.

Development and applications of a concentrating membrane osmometer for colloid solutions

“…17 Yousef used a pressure transducer for the osmotic pressure measurements but the overall time for measurement equilibrium remained approximately 5-6 h. 17 Similar time requirements are reported in other studies where the osmotic pressure profile is generated. [18][19][20][21] Hale et al ( 2018) modified the osmometer further by increasing the volume of the solvent-side chamber of the device. This ultimately acted as an infinite sink and eliminated solution-side concentration corrections.…”

“…Nevertheless, excessive sample preparation time and material use were not eliminated. 21 Overall, a time commitment on the order of days is required to generate a single osmotic pressure profile.…”

“…17,22 Recent observations show that the osmotic pressure profile of highly concentrated self-crowded protein solutions provides insight into protein hydration and ion binding. 17,18,20,21,[23][24][25][26][27] These are critical parameters in characterizing novel proteins. For many proteins of interest, the costs to providing gram quantities of protein to generate the osmotic pressure profile may be prohibitive.…”

“…Consequently, any error analysis is representative of the regression of the data to a proposed model. [15][16][17]21,23 An exception to this is the osmotic pressure profile for bovine serum albumin (BSA) in 0.7 M NaCl at pH 6.3 reported by Kappos and Pauly (1966). 28 These investigators showed error of as much as 15% in the osmotic pressure measurement for their highest concentration measurement.…”

“…The concentration of the solutions was determined by dividing the amount of protein or salt by the volume of solvent used to make the solution. The volume of solvent includes volume of protein or salt in the solution using the specific volume of the protein or the density of the salt.The general osmotic pressure experimental setup is equivalent to the design used for the standard membrane osmometer reported byHale et al (2018) 21. However, a single sample is used here to determine the concentration profile region of interest.…”