Side chain electrostatic interactions and pH‐dependent expansion of the intrinsically disordered, highly acidic carboxyl‐terminus of γ‐tubulin

Abstract

Intramolecular electrostatic attraction and repulsion strongly influence the conformational sampling of intrinsically disordered proteins and domains (IDPs). In order to better understand this complex relationship, we have used nuclear magnetic resonance to measure side chain pKa values and pH‐dependent translational diffusion coefficients for the unstructured and highly acidic carboxyl‐terminus of γ‐tubulin (γ‐CT), providing insight into how the net charge of an IDP relates to overall expansion or collapse of the conformational ensemble. Many of the pKa values in the γ‐CT are shifted upward by 0.3–0.4 units and exhibit negatively cooperative ionization pH profiles, likely due to the large net negative charge that accumulates on the molecule as the pH is raised. pKa shifts of this magnitude correspond to electrostatic interaction energies between the affected residues and the rest of the charged molecule that are each on the order of 1 kcal mol−1. Diffusion of the γ‐CT slowed with increasing net charge, indicative of an expanding hydrodynamic radius (rH). The degree of expansion agreed quantitatively with what has been seen from comparisons of IDPs with different charge content, yielding the general trend that every 0.1 increase in relative charge (|Q|/res) produces a roughly 5% increase in rH. While γ‐CT pH titration data followed this trend nearly perfectly, there were substantially larger deviations for the database of different IDP sequences. This suggests that other aspects of an IDP's primary amino acid sequence beyond net charge influence the sensitivity of rH to electrostatic interactions.

DispHred: A Server to Predict pH-Dependent Order–Disorder Transitions in Intrinsically Disordered Proteins

“…At the same time, IDPs are extremely sensitive to environmental conditions; an effect often disregarded in predictive approaches. Among the different parameters that may affect IDPs' properties, the solution pH has a significant impact, mainly due to the high prevalence of ionizable residues in these polypeptides [14,15,17,29]. In this work, we demonstrated that the effect of pH on the disordered nature of a protein sequence could be easily predicted by evaluating the changes in protein charge and hydrophobicity as a function of this parameter.…”

Driving forces of the complex formation between highly charged disordered proteins

“…Charge regulation is likely to be negligible in the salt concentration range where we studied ProTα-H1 complex formation experimentally (see SI Appendix for details and SI Appendix , Fig. S4 ) ( 74 , 75 ) and is therefore inconsequential for the interpretation of theoretical thermodynamic estimates; however, the estimates of the single-chain dimensions are slightly affected at low salt concentrations (see SI Appendix for details and SI Appendix , Fig. S4 ).…”

Fabrication of Fully Negatively Charged Layer-by-Layer Nanofilms with pH-Induced Remarkable Swelling–Shrinking Properties

“…It involves the alternate adsorption of two different polymers onto substrates, resulting in the gradual formation of a nanofilm. − LbL assembly can be driven by numerous interactions, including electrostatic interaction, , hydrogen bond, − covalent bond, − hydrophobic interaction, and biological interaction . Of these, electrostatic interaction stands out as the primary and most widely used driving force because of its easily adjustable parameters. − So, polyelectrolytes (PEs) have become the first choice for LbL nanofilm fabrication. However, it was not until the 1990s that Decher and Hong fabricated multilayer films by consecutive adsorption of polyanions and polycations, a more versatile technique that relies on solutions of macromolecules and could thus be successfully extended to other materials. ,, The wide range of materials makes it possible for the fabricated PE nanofilms to be applied in many fields, like regulating the cell environment and surface modification for different functions.…”