Involvement of tyrosine-76 of the kringle 2 domain of tissue-type plasminogen activator in its thermal stability and its omega-amino acid ligand binding site.

A series of conservative and radical mutations have been made at an aromatic residue, Y 76 , of the isolated kringle 2 domain of tissue-type plasminogen activator ([K2 tPA ) in order to assess the importance of this residue in the ligand binding properties and structural stability of this protein domain. We have successfully expressed in Escherichia coli r-[K2 tPA ] variants with the following amino acid mutations at Y 76 : Y 76 →A, Y 76 →E, Y 76 →F, Y 76 →K, Y 76 →L, Y 76 →Q, and Y 76 →W