Stereochemical aspects of amine substrate attachment to acyl intermediates of transglutaminases. Human blood plasma enzyme (activated coagulation factor XIII) and guinea pig liver enzyme.

Some preliminary proposals as to the mode of amine substrate attachment to acyl intermediates of guinea pig liver transglutaminase and human blood coagulation factor XIIIa were formulated from substrate and inhibitor studies (Gross, M., Whetzel, N. K., and Folk, J. E. (1977) J. Biol. Chem. 252, 3752-3759). The present data supply more concrete explanations for the stereopreference toward peptide-bound L.-lysine residues and for the increase in specificity resulting from the nonpolar side chain of an L-amino acid residue on the amino side of, and directly adjacent to, the substrate lysine residue. The amines tested here are: (a) peptide derivatives of the basic structure NO-acetyl-Glyz-XX-X-Glyz where X-X-X is Gly-Lys-Gly, Leu-Lys-Gly, and Gly-Lys-Leu, and where all combinations of optical forms of Lys and Leu are used; (b) the D and L forms of lysine, their a-aminoand carboxyl-blocked derivatives, and several analogs of lysine; and, (c) amides of the general structures, R1CH&ONHCH2R2, R2CH2S02NHCHzRz, and R1CH2NHCOCH2R2, where R1 is any hydrophobic group identical in structure with the side chain of an amino acid and Rz is the side chain of lysine, ie. -(CHz)dNHz. Specificities for these compounds fall in general into three classes: 1) low specificity toward peptide-bound D-lysine residues; 2) intermediate specificity for peptide derivatives of L-lysine with the exception of the heptapeptide derivative with the I,-LeuI,-Lys sequence, for analogs of lysine that contain no free a-amino or free carboxyl groups, and for amides of the structure R~CHZNHCOCHZRZ; and 3) high specificity for iV”-acetyl-Glyz-L-Leu-L-Lys-Gly3 and for amides of the structures RICH&ONHCHzRz and R1CH2S02NHCHzR2. These findings, together with those obtained earlier, form a basis for the following concepts. Peptide chains containing lysine residues are aligned along the surface of the enzymes in a single specific direction. This unidirectional alignment is dictated by some feature of enzyme topography that requires a specific fit of the peptide bond composed through the a-amino group of the lysine residue. Stereopreference resides in proper orientation of the a-hydrogen atom and the side chain of the L-lysine residue with respect to the enzyme surface. There is a binding site on the enzymes for the hydrophobic side chain of an L-amino acid residue that is located on the amino side of, and directly adjacent to, a substrate lysine residue. An amine attachment site