Comprehensive analysis of transglutaminase substrate preference by cDNA display coupled with next-generation sequencing and bioinformatics.

cDNA display is an in vitro display technology based on a covalent linkage between a protein and its corresponding mRNA/cDNA, widely used for the selection of proteins and peptides from large libraries (1012) in a high throughput manner, based on their binding affinity. Here, we developed a platform using cDNA display and next-generation sequencing (NGS) for rapid and comprehensive substrate profiling of transglutaminase 2 (TG2), an enzyme crosslinking glutamine and lysine residues in proteins. After screening and selection of the control peptide library randomized at the reactive glutamine, a combinatorial library of displayed peptides randomized at positions - 1, + 1, + 2, and + 3 from the reactive glutamine was screened followed by NGS and bioinformatic analysis, which indicated a strong preference of TG2 towards peptides with glutamine at position - 1 (Gln-Gln motif), and isoleucine or valine at position + 3. The highly enriched peptides indeed contained the indicated sequence and showed a higher reactivity as TG2 substrates than the peptide previously selected by phage display, thus representing the novel candidate peptide probes for TG2 research. Furthermore, the obtained information on substrate profiling can be used to identify potential TG2 protein targets. This platform will be further used for the substrate profiling of other TG isozymes, as well as for the selection and evolution of larger biomolecules.

In situ detection of active transglutaminases for keratinocyte type (TGase 1) and tissue type (TGase 2) using fluorescence-labeled highly reactive substrate peptides.

Transglutaminase is a calcium-dependent enzyme that posttranslationally modifies proteins by cross-linking between glutamine and lysine residues or attachment of a primary amine to specific polypeptide-bound glutamine residues. Eight isozymes play essential roles in various mammalian biological processes. The authors have recently identified 12­amino acid preferred substrate peptide sequences that are highly reactive and act in an isozyme-specific manner. In this study, a rapid, isozyme-specific, and sensitive detection of active keratinocyte type (TGase 1) and tissue type (TGase 2) was successful using fluorescence-labeled peptides. This procedure involved using whole-body sections of a mouse to extensively analyze the tissue distribution of both enzymes that revealed clearly distinct patterns. Strong active TGase 1 was observed in epithelial tissues such as tongue, developing teeth, forestomach, and skin epidermis. Significantly active TGase 2 was observed in various types of tissues as predicted and at particularly higher levels in the intestinal mucosa, muscle membrane, and whole veins in the liver. This manuscript contains online supplemental material at http://www.jhc.org. Please visit this article online to view these materials.