Effect of Intrinsic Disorder and Self-Association on the Translational Diffusion of Proteins: The Case of α-Casein

Abstract

Translational diffusion is the major mode of macromolecular transport in leaving organisms, and therefore it is vital to many biological and biotechnological processes. Although translational diffusion of proteins has received considerable theoretical and experimental scrutiny, much of that attention has been directed toward the description of globular proteins. The translational diffusion of intrinsically disordered proteins (IDPs), however, is much less studied. Here, we use a pulsed-gradient nuclear magnetic resonance technique (PFG NMR) to investigate the translational diffusion of a disordered protein in a wide range of concentrations using α-casein that belongs to the class of natively disordered proteins as an example.

Effect of Reducing Agent TCEP on Translational Diffusion and Supramolecular Assembly in Aqueous Solutions of α-Casein

“…Both diffusion attenuations are monoexponential and coincide in the whole measurement range. The diffusion coefficient of α-casein, determined from the slope of diffusion attenuations, equals to 2.97 ± 0.14 × 10 −11 m 2 /s (Table 1), which is in agreement with our previous data 20 . Similarly, α-casein diffusion coefficients were identical in the 1 % α-casein solution in the presence or absence of 10 molar TCEP excess (data not shown).…”

“…The analysis of NMR diffusion data was performed as described previously 20 . Monoexponential diffusion attenuation of the spin echo amplitude, A ( g 2 ), was described by the following equation with a single diffusion coefficient: A(g2)A(0)=exp(−γ2δ2g2tdD), where A (0) is the spin echo amplitude at g = 0, γ is the gyromagnetic ratio for protons, and t d = Δ - δ /3 is the diffusion time.…”

“…NMR diffusion measurements provide a sensitive and direct method for studying the association in protein solutions because the translational diffusion coefficient is inversely proportional to the size of diffusing species and is highly sensitive to obstacles present in solution 19 . In our recent study, we used pulsed-field gradient NMR spectroscopy to investigate the translational diffusion in aqueous solutions of α-casein in a broad range of protein concentrations 20 . We have found that if the concentration of protein increases above ~5% (wt.…”

Sodium caseinate as a particulate emulsifier for making indefinitely recycled pH-responsive emulsions

“…as 1 -casein is a triblock copolymer, and monomeric b-casein and k-casein have both hydrophobic and hydrophilic extremities. [23][24][25][26][27][28][29] NaCas, which is derived from casein and has a highly disordered structure, is a robust amphipathic protein that typically associates into spherical micelles (sub-micelles) with diameters in the range of 20-40 nm under neutral and weakly basic conditions (for example, pH 8.0) ( Fig. 1a 1 ).…”

On the Need to Develop Guidelines for Characterizing and Reporting Intrinsic Disorder in Proteins

“…Figure displays a simple example of using population‐statistics to interpret intrinsic disorder predictions of total disorder content and long disordered regions in two disordered proteins and two ordered proteins. α‐Casein and Spinophilin are characterized as intrinsically disordered proteins, whereas serum albumin and myoglobin are considered as ordered proteins. Figure demonstrates these disorder/order classifications are captured by the relative standing with respect to the H. sapiens proteome.…”