The present disclosure relates to a recombinant transglutaminase (TG) substrate having an amino acid sequence of the FKBP domain of an FKBP polypeptide, wherein the “insert-in-flap” (IF) domain thereof is, at least in part, replaced by an amino acid sequence (“Q-tag”) of 5 to 20 amino acids with a sequence having at least 80% sequence identity to the YRYRQ portion of the peptide sequence X1-YRYRQ-X2 (SEQ ID NO. 1), and wherein said TG substrate is a substrate for the TG function of the Kutzneria albida TG. The present disclosure furthermore relates to uses of said substrate.
