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pH-induced structural transitions of caseins

Paper ID Volume ID Publish Year Pages File Format Full-Text
31177 44561 2007 9 PDF Available
Title
pH-induced structural transitions of caseins
Abstract

Caseins are relatively small (molecular mass ∼20 kDa), unstructured milk proteins of which the main components are referred to as αs-, β- and κ-casein. All three components lack a compact folded conformation, which can be ascribed to a combination of their low overall hydrophobicity and high net charge. Structural transitions of the three caseins in response to variation of pH were investigated using fluorescence and circular dichroism (CD) spectroscopy. Tryptophan emission parameters (intensity and wavelength of emission maximum) and CD spectra showed that at neutral and alkaline pH the caseins exist predominantly in random coil conformation. As the solvent is made acidic the added protons compensate the negative charges on the caseins and reduce the repulsion between like charged residues, allowing the casein chains to fold. At the pI (pH 4–5), the net charge on the protein tends to zero and the protein should approach its maximally structured state. Below pI, the uncompensated charges and their interactions reappear, resulting in slackening of the compact structure and formation of a partially unfolded intermediate. These conclusions were borne out by the biphasic pH-dependence of the fluorescence emission parameters of Trp as well as of ANS incubated with the caseins. Measurement of the efficiency of energy transfer between Trp (donor) and ANS (acceptor) and of the CD spectra of caseins as functions of pH were also consistent with this scenario.

Keywords
Casein; Natively unfolded; Isoelectric point; Fluorescence; Circular dichroism; Molten globule
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pH-induced structural transitions of caseins
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Publisher
Database: Elsevier - ScienceDirect
Journal: Journal of Photochemistry and Photobiology B: Biology - Volume 87, Issue 3, 26 June 2007, Pages 191–199
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Bioengineering
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us