K-Casein terminates casein micelle build-up by its 'soft' secondary structure

Krisztina Nagy, Gyorgy Varo, Balazs Szalontai

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Abstract

In our previous paper (Nagy et al. in J Biol Chem 285:38811-38817, 2010) by using a multilayered model system, we showed that, from α-casein, aggregates (similar to natural casein micelles) can be built up step by step if Ca-phosphate nanocluster incorporation is ensured between the protein adsorption steps. It remained, however, an open question whether the growth of the aggregates can be terminated, similarly to in nature with casein micelles. Here, we show that, in the presence of Ca-phosphate nanoclusters, upon adsorbing onto earlier α-casein surfaces, the secondary structure of α-casein remains practically unaffected, but k-casein exhibits considerable changes in its secondary structure as manifested by a shift toward having more β-structures. In the absence of Ca-phosphate, only k-casein can still adsorb onto the underlying casein surface; this k-casein also expresses considerable shift toward β-structures. In addition, this k-casein cover terminates casein aggregation; no further adsorption of either α-or k-casein can be achieved. These results, while obtained on a model system, may show that the Ca-insensitive k-casein can, indeed, be the outer layer of the casein micelles, not only because of its 'hairy' extrusion into the water phase, but because of its 'softer' secondary structure, which can 'occlude' the interacting motifs serving casein aggregation. We think that the revealed nature of the molecular interactions, and the growth mechanism found here, might be useful to understand the aggregation process of casein micelles also in vivo.

Original languageEnglish
Pages (from-to)959-968
Number of pages10
JournalEuropean Biophysics Journal
Volume41
Issue number11
DOIs
Publication statusPublished - Nov 1 2012

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Keywords

  • Atomic force microscopy (AFM)
  • Attenuated total reflection Fourier-transform infrared (ATR-FTIR)
  • Casein micelle
  • K-Casein
  • α-Casein

ASJC Scopus subject areas

  • Biophysics

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