Minithioredoxin: A folded and functional peptide fragment of thioredoxin

A peptide fragment comprising the first 83 residues from the N-terminus off . coli thioredoxin is purified by hydroxylamine cleavage of the intact prot ein. At physiological pH, the secondary and tertiary structure contents of the peptide are 70 and 35%, respectively, compared to the intact protein. P eptide 83 is able to display dual biological functions of thioredoxin, name ly, a substrate for the enzyme E. coli thioredoxin-reductase and a processi vity factor of T7 DNA polymerase. At present, peptide 83 represents the min imum functional and folding unit of thioredoxin. The highly conserved resid ue Phe 81 appears to play an important role in the folding of peptide 83, a s judged from the packing analysis. Peptide 83 also mimics a particular kin etic folding intermediate of thioredoxin in terms of spectral properties an d may serve as an equilibrium peptide model for the former. (C) 1999 Academ ic Press.