TRANSGLUTAMINASE FACTOR-XIII USES PROTEINASE-LIKE CATALYTIC TRIAD TO CROSS-LINK MACROMOLECULES

The X-ray crystal structure of human transglutaminase factor XIII has revealed a cysteine proteinase-like active site involved in a crosslin king reaction and not proteolysis. This is among the first observation s of similar active sites in 2 different enzyme families catalyzing a similar reaction in opposite directions. Although the size and overall protein fold of factor XIII and the cysteine proteinases are quite di fferent, the active site and the surrounding protein structure share s tructural features suggesting a common evolutionary lineage. Here we p resent a description of the residues in the active site and the struct ural evidence that the catalytic mechanism of the transglutaminases is similar to the reverse mechanism of the cysteine proteinases.