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Effective Interactions and Colloidal Stability of Bovine γ-Globulin in Solution
Interactions and phase behavior of γ-globulins are of fundamental interest in biophysical and pharmaceutical research, as these are among the most abundant proteins in blood plasma. In this work, we report the characterization of the oligomeric state of bovine γ-globulin, the effective protein–protein interactions, and the colloidal stability in aqueous solution as a function of protein concentrat
Strong Isotope Effects on Effective Interactions and Phase Behavior in Protein Solutions in the Presence of Multivalent Ions
In this article, we have studied the influence of the isotopic composition of the solvent (H2O or D2O) on the effective interactions and the phase behavior of the globular protein bovine serum albumin in solution with two trivalent salts (LaCl3 and YCl3). Protein solutions with both salts exhibit a reentrant condensation phase behavior. The condensed regime (regime II) in between two salt concentr
Cation-Induced Hydration Effects Cause Lower Critical Solution Temperature Behavior in Protein Solutions
The phase behavior of protein solutions is important for numerous phenomena in biology and soft matter. We report a lower critical solution temperature (LCST) phase behavior of aqueous solutions of a globular protein induced by multivalent metal ions around physiological temperatures. The LCST behavior manifests itself via a liquid-liquid phase separation of the protein-salt solution upon heating.
Analytical correlation functions for motion through diffusivity landscapes
Diffusion of a particle through an energy and diffusivity landscape is a very general phenomenon in numerous systems of soft and condensed matter. On the one hand, theoretical frameworks such as Langevin and Fokker-Planck equations present valuable accounts to understand these motions in great detail, and numerous studies have exploited these approaches. On the other hand, analytical solutions for
On the question of two-step nucleation in protein crystallization
We report a real-time study on protein crystallization in the presence of multivalent salts using small angle X-ray scattering (SAXS) and optical microscopy, focusing particularly on the nucleation mechanism as well as on the role of the metastable intermediate phase (MIP). Using bovine beta-lactoglobulin as a model system in the presence of the divalent salt CdCl2, we have monitored the early sta
Hierarchical molecular dynamics of bovine serum albumin in concentrated aqueous solution below and above thermal denaturation
The dynamics of proteins in solution is a complex and hierarchical process, affected by the aqueous environment as well as temperature. We present a comprehensive study on nanosecond time and nanometer length scales below, at, and above the denaturation temperature Td. Our experimental data evidence dynamical processes in protein solutions on three distinct time scales. We suggest a consistent phy
Salt-Induced Universal Slowing Down of the Short-Time Self-Diffusion of a Globular Protein in Aqueous Solution
The short-time self-diffusion D of the globular model protein bovine serum albumin in aqueous (D2O) solutions has been measured comprehensively as a function of the protein and trivalent salt (YCl3) concentration, noted cp and cs, respectively. We observe that D follows a universal master curve D(cs,cp) = D(cs = 0,cp) g(cs/cp), where D(cs = 0,cp) is the diffusion coefficient in the absence of salt
Real-time observation of nonclassical protein crystallization kinetics
We present a real-time study of protein crystallization of bovine-lactoglobulin in the presence of CdCl2 using small-angle X-ray scattering and optical microscopy. From observing the crystallization kinetics, we propose the following multistep crystallization mechanism that is consistent with our data. In the first step, an intermediate phase is formed, followed by the nucleation of crystals withi
Anomalous and anisotropic nanoscale diffusion of hydration water molecules in fluid lipid membranes
We have studied nanoscale diffusion of membrane hydration water in fluid-phase lipid bilayers made of 1,2-dimyristoyl-3-phosphocholine (DMPC) using incoherent quasi-elastic neutron scattering. Dynamics were fit directly in the energy domain using the Fourier transform of a stretched exponential. By using large, 2-dimensional detectors, lateral motions of water molecules and motions perpendicular t
Gold nanoparticles decorated with oligo(ethylene glycol) thiols : Surface charges and interactions with proteins in solution
We have studied oligo(ethylene glycol) (OEG) thiol self-assembled monolayer (SAM) coated gold nanoparticles (AuOEG) and their interactions with proteins in solutions using electrophoretic and dynamic light scattering (ELS and DLS). The results are compared with poly(ethylene glycol) (PEG) thiol coated AuNPs (AuPEG). We show that both AuOEG and AuPEG particles carry a low net negative charge and ar
Effective interactions in protein-salt solutions approaching liquid-liquid phase separation
We present an experimental study combined with a theoretical discussion of the effective interactions in protein solutions approaching a liquid-liquid phase separation (LLPS) induced by addition of multivalent metal ions. The reduced second virial coefficient, B2/B2HS, is used to describe the interaction and discussed with theoretical predictions for colloidal systems. We have determined the salt
Protein cluster formation in aqueous solution in the presence of multivalent metal ions-a light scattering study
The formation of protein clusters as precursors for crystallization and phase separation is of fundamental and practical interest in protein science. Using multivalent ions, the strengths of both long-range Coulomb repulsion and short-range attraction can be tuned in protein solutions, representing a well-controlled model system to study static and dynamic properties of clustering during the trans
Ion-activated attractive patches as a mechanism for controlled protein interactions
The understanding of protein interactions to control phase and nucleation behavior of protein solutions is an important challenge for soft matter, biological and medical research. Here, we present ion bridges of multivalent cations between proteins as an ion-activated mechanism for patchy interaction that is directly supported by experimental findings in protein crystals. A deep understanding of e
Competing salt effects on phase behavior of protein solutions : Tailoring of protein interaction by the binding of multivalent ions and charge screening
The phase behavior of protein solutions is affected by additives such as crowder molecules or salts. In particular, upon addition of multivalent counterions, a reentrant condensation can occur; i.e., protein solutions are stable for low and high multivalent ion concentrations but aggregating at intermediate salt concentrations. The addition of monovalent ions shifts the phase boundaries to higher
Reentrant condensation, liquid"liquid phase separation and crystallization in protein solutions induced by multivalent metal ions
We briefly summarize the recent progress in tuning protein interactions as well as phase behavior in protein solutions using multivalent metal ions. We focus on the influence of control parameters and the mechanism of reentrant condensation, the metastable liquid"liquid phase separation and classical vs. nonclassical pathways of protein crystallization.
Diffusion and dynamics of γ-globulin in crowded aqueous solutions
Dynamics in protein solutions is essential for both protein function and cellular processes. The hierarchical complexity of global protein diffusion, side-chain diffusion, and microscopic motions of chemical groups renders a complete understanding challenging. We present results from quasi-elastic neutron scattering on protein solutions of γ-globulin over a wide range of volume fractions. Translat
The role of cluster formation and metastable liquid - Liquid phase separation in protein crystallization
We discuss the phase behavior and in particular crystallization of a model globular protein (beta-lactoglobulin) in solution in the presence of multivalent electrolytes. It has been shown previously that negatively charged globular proteins at neutral pH in the presence of multivalent counterions undergo a "re-entrant condensation (RC)" phase behavior (Zhang et al., Phys. Rev. Lett., 2008, 101, 14
Hydration and interactions in protein solutions containing concentrated electrolytes studied by small-angle scattering
During protein crystallization and purification, proteins are commonly found in concentrated salt solutions. The exact interplay of the hydration shell, the salt ions, and protein-protein interactions under these conditions is far from being understood on a fundamental level, despite the obvious practical relevance. We have studied a model globular protein (bovine serum albumin, BSA) in concentrat
Interplay of pH and binding of multivalent metal ions : Charge inversion and reentrant condensation in protein solutions
Tuning of protein surface charge is a fundamental mechanism in biological systems. Protein charge is regulated in a physiological context by pH and interaction with counterions. We report on charge inversion and the related reentrant condensation in solutions of globular proteins with different multivalent metal cations. In particular, we focus on the changes in phase behavior and charge regulatio