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 (10) 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.