[Show abstract][Hide abstract] ABSTRACT: The effective interactions and phase behavior of protein solutions under strong electrostatic coupling conditions are difficult to understand due to the complex charge pattern and irregular geometry of protein surfaces. This distinguishes them from related systems such as DNA or conventional colloids. In this work, we discuss the question of universality of the reentrant condensation (RC) of proteins in solution induced by multivalent counterions, i.e., redissolution on adding further salts after phase separation, as recently discovered (Zhang et al., Phys Rev Lett 2008; 101:148101). The discussion is based on a systematic investigation of five different proteins with different charge patterns and five different multivalent counterions. Zeta potential measurements confirm the effective charge inversion of proteins in the reentrant regime via binding of multivalent counterions, which is supported by Monte Carlo simulations. Charge inversion by trivalent cations requires an overall negative net charge of the protein. Statistical analysis of a representative set of protein sequences reveals that, in theory, this effect could be possible for about half of all proteins. Our results can be exploited for the control of the phase behavior of proteins, in particular facilitating protein crystallization.
Proteins Structure Function and Bioinformatics 12/2010; 78(16):3450-7. · 3.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The electrostatic behavior of biomolecules solved in water can be described by an elliptic system of partial differential equations for the potential. In previous studies, this system has been solved by the Boundary Element Method (BEM).In this paper, we apply the Explicit Jump Immersed Interface Method (EJIIM) as an alternative method to the BEM. Such a finite difference approach allows for a completely automatized software for analyzing biomolecules in their natural surrounding.The new method shows excellent agreement with the BEM results and has good convergence properties and runtimes. In addition, in contrast to the BEM, where the fundamental solutions of operators are necessary, the EJIIM approach can be easily extended to more complex, especially nonlinear models.
Journal of Computational Physics 06/2010; · 2.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present a few-mode Galerkin model for convection in binary fluid layers subject to an approximation to realistic horizontal boundary conditions at positive separation ratios. The model exhibits convection patterns in form of rolls and squares. The stable squares at onset develop into stable rolls at higher thermal driving. In between, a regime of a so-called cross roll structure is found. The results of our few-mode model are in good agreement with both experiments and numerical multimode simulations.
[Show abstract][Hide abstract] ABSTRACT: Negatively charged globular proteins in solution undergo a condensation upon adding trivalent counterions between two critical concentrations C and C, C <C. This reentrant condensation behavior above C is caused by short-ranged electrostatic interactions between multivalent cations and acidic residues, mechanistically different from the case of DNA. Small-angle x-ray scattering indicates a short-ranged attraction between counterion-bound proteins near C and C. Monte Carlo simulations (under these strong electrostatic coupling conditions) support an effective inversion of charge on surface side chains through binding of the multivalent counterions.