Addressing substrate glutamine requirements for tissue transglutaminase using substance P analogues

We have investigated the effect on the substrate requirements for guinea pi g liver (tissue) transglutaminase of a set of 11 synthetic glutamine substi tution analogues making up the full sequence of the naturally occurring tis sue transglutaminase substrate substance P. While a number of peptide seque nces derived from proteins that are well-recognized as tissue transglutamin ase substrates have been studied, the enzyme activity using substitution an alogues of full-length natural substrates has not been investigated as thor oughly. Thus, our set of substance P analogues only differs from one to oth er by one amino acid mutation while the length (of the peptide) is maintain ed as in the natural parent peptide, Our results indicate that a glutamine residue is not recognized as substrate by the enzyme whether it is placed a t the N- or C-terminal or between two positively charged residues or betwee n two proline residues. To further address the effect on enzyme activity of charged amino acids in the vicinity of the reactive glutamine residue, a n ew set of synthetic charge replacement analogues of substance P has been al so studied. Together, the results have identified new minimal requirements for modification of a particular glutamine residue in a polypeptide chain. It would be of interest to set up a full set of such requirements in order to highlight potential glutamine residues as enzyme targets in the growing list of proteins that are being described as transglutaminase substrates. ( C) 1999 Federation of European Biochemical Societies.