Stable monomeric intermediate with exposed Cys-119 is formed during heat denaturation of beta-lactoglobulin.
The role of the free sulfhydryl group of beta-lactoglobulin in the formation of a stable non-native monomer during heat-treatment of beta-lactoglobulin solutions was investigated. Two concomitant events occurred at the earlier stage of heating: unfolding of native globular monomer and intramolecular sulfhydryl/disulfide exchange reaction. Thus, two denatured monomeric species were formed: a non-native monomer with exposed Cys-121 (Mcys121) which became reversible after cooling, and a stable non-native monomer with exposed Cys-119 (Mcys119) which exhibited both a larger hydrodynamic conformation than native monomer and low solubility at pH 4.7. The results also show that the formation of these monomeric species throughout heat-induced denaturation of native beta-lg monomers is faster than their subsequent aggregation. A mechanism describing the behavior of beta-lg denaturation/aggregation during heat-treatment under selected conditions (5.8 mg/ml, low ionic strength, pH 6.6, 85 degrees C) is presented.
Croguennec
Thomas
T
ENSA-INRA-CS 84215-65, rue de St Brieuc, Rennes cedex 35 042, France. Thomas.Croguennec@agrorennes.educagri.fr
Bouhallab
Saïd
S
Mollé
Daniel
D
O'Kennedy
Brendan T
BT
Mehra
Raj
R
D000818:Animals; D002845:Chromatography; D003545:Cysteine / Q000737:chemistry* / Q000378:metabolism; D004220:Disulfides / Q000737:chemistry; D005033:Ethylmaleimide / Q000737:chemistry; D006358:Hot Temperature; D007782:Lactoglobulins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D013056:Spectrophotometry, Ultraviolet; D013438:Sulfhydryl Compounds / Q000737:chemistry
D004220:Disulfides; D007782:Lactoglobulins; D013438:Sulfhydryl Compounds; D003545:Cysteine; D005033:Ethylmaleimide