Thermally-induced protein unfolding is commonly described with the two-state model. This model assumes only two types of protein molecules in solution, the native (N) and the denatured, unfolded (U) protein. In reality, protein unfolding is a multistep process, even if intermediate states are only sparsely populated. As an alternative approach we explore the Zimm–Bragg theory, originally developed for the α-helix-to-random coil transition of synthetic polypeptides. The theory includes intermediate structures with concentrations determined by the cooperativity of the unfolding reaction. We illustrate the differences between the two-state model and the Zimm–Bragg theory with measurements of apolipoprotein A-1 and lysozyme by differential scanning calorimetry (DSC) and CD spectroscopy. Nine further protein examples are taken from the literature. The Zimm–Bragg theory provides a perfect fit of the calorimetric unfolding transitions for all proteins investigated. In contrast, the transition curves and enthalpies predicted by the two-state model differ considerably from the experimental results. Apolipoprotein A-1 is ~50% α-helical at ambient temperature and its unfolding follows the classical α-helix-to-random coil equilibrium. The unfolding of proteins with little α-helix content, such as lysozyme, can also be analyzed with the Zimm–Bragg theory by introducing the concept of ‘folded’ and ‘unfolded’ peptide units assuming an average unfolding enthalpy per peptide unit. DSC is the method of choice to measure the unfolding enthalpy, , but CD spectroscopy in combination with the two-state model is often used to deduce the unfolding enthalpy. This can lead to erroneous result. Not only are different enthalpies required to describe the CD and DSC transition curves but these values deviate distinctly from the experimental result. In contrast, the Zimm–Bragg theory predicts the DSC and CD unfolding transitions with the same set of parameters.
from #AlexandrosSfakianakis via Alexandros G.Sfakianakis on Inoreader http://ift.tt/2zif7Px
via IFTTT
Εγγραφή σε:
Σχόλια ανάρτησης (Atom)
Δημοφιλείς αναρτήσεις
-
Résumé L'extrait hydrométhanolique des parties aériennes d' Origanum glandulosum Batt. et Trab. a été étudié pour sa composition ...
-
Abstract Ethylene-octene copolymer (EOC)/organoclay nanocomposite was cured by peroxide in an internal mixer for different time periods. L...
-
http://ift.tt/2qKmhUL
-
Abstract Understanding the spatial distribution of PM 2.5 concentration and its contributing environmental variables is critical to devel...
-
Kinematic, Kinetic and Surface Electromyography Analysis Following Zygomatic Fracture ReconstructionAbstract The surgical indications of zygomatic fracture include aesthetic and functional impairment. No standard method exists for assessi...
-
Abstract The molecular genetic modifications in multiple genes involved in folate and homocysteine metabolism play the pivotal role in the...
-
Respiratory Polysomnographic Findings in Patients Treated Primarily for Unilateral Cleft Lip and Palate. Cleft Palate Craniofac J. 201...
-
Abstract AFLP analysis of 144 samples of tetraploid wheat species, including cultivars and landraces of Triticum durum from Azerbaijan, w...
-
Abstract The purpose of this study was to determine the different kinds and concentrations of intermediates, and investigate on the effect...
Δεν υπάρχουν σχόλια:
Δημοσίευση σχολίου