Protein Engineering, Vol. 13, No. 5, 323-327,
May 2000
© 2000 Oxford University Press
Improvement in the efficiency of formyl transfer of a GAR transformylase hybrid enzyme
152 Davey Laboratory, Department of Chemistry, The Pennsylvania State University, University Park, PA 16802-6300, USA
A hybrid glycinamide ribonucleotide transformylase was assembled from two protein domains that were treated as discrete modules. One module contained the ribonucleotide binding domain from the purN glycinamide ribonucleotide transformylase; the second module contained the catalytic machinery and the formyl tetrahydrofolate binding domain from the enzyme encoded by purU, formyl tetrahydrofolate hydrolase. The resultant enzyme showed 0.1% catalytic activity of the wild-type glycinamide ribonucleotide transformylase enzyme but had a formyl transfer efficiency of 10%. A combinatorial mutagenesis approach was used to improve the solubility and formyl transfer properties of the hybrid enzyme. The mutagenized hybrid glycinamide ribonucleotide transformylase was initially expressed as a fusion to the 
-peptide of ß-galactosidase. Clones were selected for improvement in solubility by determining which clones were capable of -complementation using a blue/white screen. One clone was further characterized and found to have an improved efficiency of transfer of the ribonucleotide increasing this property to >95%.