Abstract
Microbial transglutaminase is used in the food industry to improve texture by catalyzing protein cross-linking. Casein is a well-known transglutaminase substrate, but the complete role of glutamine (Q) and lysine (K) residues in its cross-linking is not fully understood. In this study, we describe the characterization of microbial Transglutaminase -modified casein using a combination of immunological and proteomic techniques. Using 5-(biotinamido)pentylamine as an acyl acceptor probe, three Q residues of β-casein and one of αs1-casein were found to participate as acyl donors. However, no Q-residues were involved in network formation with κ-casein or αs2-casein. Q and K residues in the e-(γ-glutamyl)lysine-isopeptide bonds β-casein were identified by nanoelectrospray tandem mass spectrometry of the proteolytic digests. This work reports our progress toward a better understanding of the function and mechanism of action of microbial transglutaminase-mediated proteins. The results suggest a possible role for transglutaminase in the formation of casein micelles.
Highlights
Transglutaminase (TG) is one of a family of enzymes that catalyzes an acyl transfer reaction in the presence of Ca2+
In the reaction catalyzed by TG, Q residues serve as the acyl donors and ε-amino groups of lysine (K) as the acyl acceptors
This study reports the identification of several amino acid sequences of ovine CN that act as glutamine-donor substrates of microbial TG (mTG)
Summary
Transglutaminase (TG) is one of a family of enzymes that catalyzes an acyl transfer reaction in the presence of Ca2+ This reaction forms amide bonds between the ε--carboxamide groups of peptide-bound glutamine (Q) residues and a variety of primary amines [1]. Foods treated with mTG have been approved for human consumption by the US Food and Drug Administration, and its application has expanded to all foods Many food proteins such as casein (CN) are excellent substrates for TG [22,23,24], primarily due to their highly accessible and flexible open chain structure. This study reports the identification of several amino acid sequences of ovine CN that act as glutamine-donor substrates of mTG
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