The osmotic second virial coefficient for protein self-interaction: Use and misuse to describe thermodynamic nonideality

Abstract

, The osmotic second virial coefficient for protein self-interaction: use and misuse to describe thermodynamic nonideality, Analytical Biochemistry (2015),

Rigorous analysis of static light scattering measurements on buffered protein solutions

“…As re-emphasized recently [1], the inclusion of a single nonassociating protein in solvent at constant temperature gives rise to one of two situations: that in which the protein chemical potential is being monitored under the additional constraint of constant solvent chemical potential, and that in which constant pressure is the second constraint -a distinction that is overlooked in standard textbooks and most experimental studies. Studies performed under the former constraint, which applies in osmometry and size-exclusion chromatography, are the simplest to consider because small partitioning solutes (buffer components and electrolytes)…”

“…However, irrespective of the relevance of that seeming disparity, the important point to emerge from Fig. 2 is that sucrose must be regarded as a nonscattering cosolute [15]; and that other small species such as buffer components must also be regarded in similar vein [1,9,10].…”

“…The first doubts about the thermodynamic status of A 2 arose from light scattering studies reporting negative values for the osmotic second virial coefficient for protein selfinteraction [1][2][3]34]. Those reports prompted sedimentation equilibrium studies on lysozyme [35] and equine serum albumin [9] to show the ionic strength dependent decrease in B 22 to a positive, asymptotic value defined by the hard particle contribution.…”

“…However, the parameter derived therefrom (A 2 ) is not identical to the second virial coefficient for protein selfinteraction (B 22 ) that emanates from osmotic pressure, sedimentation equilibrium and sizeexclusion chromatography measurements on buffered protein solutions [1]. We were first alerted to this problem by reports of negative B 22 values from light scattering studies of protein solutions supplemented with high salt concentrations [2][3][4] -values incompatible with the statistical-mechanical concept of the osmotic second virial coefficient for protein self-interaction as an excluded volume [5,6].…”

Foreword to ‘Quantitative and analytical relations in biochemistry’—a special issue in honour of Donald J. Winzor’s 80th birthday

“…Methods for the prediction of the thermodynamic osmotic 2nd virial coefficient from structure and charge information were developed with the routine COVOL (Harding et al 1998(Harding et al , 1999 and the scope expanded to cover the determination of second virial coefficients from static light scattering measurements. Results from those methods (Deszczynski et al 2006;Winzor et al 2007b) as well as spectral studies (Wills and Winzor 2011) have allowed the testing of theory associated with the correct definition of virial coefficients (Wills et al 2015). Attention has also turned to the analogous situation in small-angle X-ray scattering studies (Scott et al 2010(Scott et al , 2011(Scott et al , 2013, which have been used to deduce the structure of components of the basement membrane protein system (Patel et al , 2012(Patel et al , 2014.…”