Ability of αs-Casein to Suppress the Heat Aggregation of Ovotransferrin

Abstract

The effects of alphas-casein on heat aggregation of ovotransferrin (OT) were studied by heating at 80 degrees C for 20 min in 10 mM phosphate buffer, pH 7.0. The heat interactions between alphas-casein and OT were followed by turbidity development and polyacrylamide gel electrophoresis. We found that alphas-casein can effectively suppress the heat-induced aggregation of heat-labile OT. The suppressive ability of alphas-casein was reduced by the presence of NaCl on heating. Dephosphorylated alphas-casein had less ability to suppress the aggregation of OT than native alphas-casein. Our results indicate that alphas-casein interacts with the heat-denatured OT through its exposed hydrophobic surface and phosphoserine residue. Such interactions seem to be important in helping to suppress the aggregation of heated OT. The suppressive effects of alphas-casein on heat aggregation of OT would be partially ascribed to the formation of transparent gel from egg white by the addition of alphas-casein.

Alpha-Casein as a Molecular Chaperone

“…In stabilising insulin, apo-and holo--lactalbumin as target proteins, -and -casein did not provide as much protection against precipitation as S-casein on a w:w and molar basis, but were similar to each other in their efficacy [18]. This was in contrast to previous reports which described greater chaperone action in -casein compared to S-casein in stabilising heat stressed catalase and reduction stressed lysozyme [110], whereas others found that S-casein was better than -casein at preventing the aggregation of heat-stressed ovotransferrin [113]. This apparent disparity in the relative chaperone performances of the casein proteins is likely to be related to their broad target protein specificities.…”

“…Since then, -and -casein have both been shown to also act as molecular chaperones [18,33,[110][111][112]. The presence of high numbers of phosphate groups in the casein proteins appears to be important for chaperone action against amorphously aggregating target proteins under both reduction and heat stress, with studies showing that removal of these in S-and -casein reduced their ability to prevent the aggregation of target proteins [113,114].…”

Invited review: Caseins and the casein micelle: Their biological functions, structures, and behavior in foods

“…For example, α S -CN is significantly better than β-CN at preventing the heat-induced aggregation of ovotransferrin (Matsudomi et al, 2004) or the reduction-induced aggregation of the insulin B-chain (Morgan et al, 2005). However, β-CN is more effective than α S -CN at inhibiting the heat-induced aggregation of catalase and the reduction-induced aggregation of lysozyme (Zhang et al, 2005).…”

“…Like sHsp, caseins are promiscuous chaperones: they stabilize a range of unrelated target proteins from amorphous aggregation induced by heat, reduction, and UV-induced stress (Bhattacharyya and Das, 1999;Matsudomi et al, 2004;Morgan et al, 2005;Zhang et al, 2005;Hassanisadi et al, 2008;Koudelka et al, 6133 2009;Treweek et al, 2011). Moreover, α S1 -and β-CN can also prevent the formation of fibrillar structures by target proteins, including α S2 -and κ-CN (Thorn et al, 2005, ovalbumin (Khodarahmi et al, 2008), and amyloid-β peptide (Carrotta et al, 2012).…”

Thermostabilization of Ovotransferrin by Anions for Pasteurization of Liquid Egg White

“…In addition to Al 3þ , many additives which inhibit the aggregation of oTf, such as sucrose, s-casein and dry-heated ovalbumin, have been reported. [12][13][14][15] In this current study, the effect of anions on the thermostability of the apo-form of oTf is investigated.…”