5-(Biotinamido)pentylamine

Transglutaminases (TGs) are a family of enzymes that catalyze Ca(2+)-dependent post-translational modification of proteins by introducing protein-protein crosslinks (between specific glutamine and lysine residues), amine incorporation, and site-specific deamidation. In this study, new amine acceptor protein substrates of TG were isolated from rat liver extract and identified using 5-(biotinamido) pentylamine, a biotinylated primary amine substrate, as a probe. TG protein substrate candidates labeled with biotin by endogenous TG activity were isolated and recovered by avidin column chromatography. Proteins with molecular masses of 40, 42, and 45 kDa were the main components of the labeled proteins. Determination of their partial amino acid sequences and immunoblotting analyses were done to identify them. The 45-kDa protein was identical with betaine-homocysteine S-methyltransferase (EC 2.2.2.5), which was identified in our previous study. The 40- and 42-kDa proteins were identified as arginase-I (EC 3.5.3.1) and fructose-1,6-bisphosphatase (EC 3.1.3.11) respectively. TG catalyzed incorporation of 5-(biotinamido) pentylamine into both arginase-I and fructose-1,6-bisphosphatase purified from rat liver was confirmed in vitro. These results suggest that these two enzymes are the new protein substrate candidates of TG and that they can be modified post-translationally by cellular TG.

A biotinamine probe, 5-(biotinamido)pentylamine, was used for biotin-labeling of proteins in HT29 colon cancer cell extracts by endogenous transglutaminase activity. The biotin-labeled protein substrates were isolated and recovered by avidin-affinity chromatography. The proteins were separated using SDS-polyacrylamide gel electrophoresis, electroblotted onto a polyvinylidene difluoride membrane, visualized using Coomassie blue, cut out, and sequenced. Amino acid sequence data identified human fructose-1,6-bisphosphate aldolase A, an intracellular protein, as a substrate for cellular transglutaminase.

Transglutaminases belong to an important family of enzymes involved in hemostasis, skin formation, and wound healing. We describe a technique for the measurement of transglutaminase activity using polystyrene microtiter plates coated with N,N'-dimethylcasein. The substrate 5-(biotinamido)pentylamine is covalently incorporated into N,N'-dimethylcasein by transglutaminase in a calcium-dependent reaction. The biotinylated product is detected by streptavidin-alkaline phosphatase and quantitated by measuring the absorbance at 405 nm following the addition of p-nitrophenyl phosphate. The assay is sensitive, specific, and linear at plasma factor XIIIa concentrations between 0.08 and 1.25 micrograms/ml and at purified guinea pig liver transglutaminase concentrations between 0.05 and 0.8 microgram/ml. The intra-assay coefficient of variation is less than 8%. The solid-phase assay was used to quantitate the transglutaminase activity in Escherichia coli extracts expressing recombinant factor XIII A-chains and to analyze factor XIIIa inhibitors. This method will facilitate the analysis of structure-function relationships of the transglutaminases using recombinant DNA methods. Furthermore, screening of natural and synthetic factor XIIIa inhibitors will be expedited by this solid-phase microtiter plate assay.