Premium
Analysis of disulphide linkages in bovine κ‐casein oligomers using two‐dimensional electrophoresis
Author(s) -
Holland John W.,
Deeth Hilton C.,
Alewood Paul F.
Publication year - 2008
Publication title -
electrophoresis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.666
H-Index - 158
eISSN - 1522-2683
pISSN - 0173-0835
DOI - 10.1002/elps.200700840
Subject(s) - chemistry , oligomer , monomer , casein , protein subunit , bovine milk , biochemistry , chromatography , organic chemistry , polymer , gene
Disulphide bonds play an important role in protein structure and function. Bovine κ‐casein (κ‐csn), an important glycoprotein in milk, contains two cysteines that can form disulphide bonds. On 2‐D gels run under nonreducing conditions the κ‐csn in milk presented a complex pattern of monomers and disulphide‐linked oligomers. Trains of spots corresponding to monomers to hexamers were observed as a result of the participation of different glycoforms and phosphoforms in oligomer formation. The dimers and trimers ran as doublets on the gel and analysis of the disulphide‐linked peptides released from them after in‐gel tryptic digestion showed they were the result of different disulphide linkages. The linkages were confirmed by MSMS. When milks with electrophoretically distinct genetic variants of κ‐csn were mixed and run on 2‐D gels, they retained their distinct patterns indicating that disulphide exchange reactions or disulphide ‘scrambling’ was not occurring during 2‐D analysis. The patterns observed represent the native distribution of κ‐csn in milk at harvest. The role and significance of the disulphide bonding of κ‐csn are discussed.