STABILITY AND FOLDING OF PRECURSOR AND MATURE TRYPTOPHAN-SUBSTITUTED RIBOSE BINDING-PROTEIN OF ESCHERICHIA-COLI

A mutant ribose binding protein (REP) of Escherichia coli was obtained by site directed mutagenesis, replacing Phe-187 in the wild-type REP (WT-REP) with a Trp residue, in order to compare its stability and fol ding behavior with those of the WT-REP, The equilibrium unfolding prop erties and the folding kinetics of these proteins were monitored by fl uorescence and circular dichroism (CD), For both WT-REP and the Trp-su bstituted REP (Trp-REP), the conformational stabilities of the precurs or proteins and the mature proteins were the same, indicating that the signal peptide had no influence on the property of the mature domain, The Phe/Trp substitution in the mature domain, however, brought about a significant decrease in the conformational stability, The signal pe ptide had an appreciable retarding effect on the folding of the precur sor Trp-REP as was reported for the WT-REP, Refolding kinetics of the WT-REP and Trp-REP showed a two-step reaction when monitored by fluore scence and by CD. (C) 1996 Academic Press, Inc.