STRUCTURES OF REVERTANT SIGNAL SEQUENCES OF ESCHERICHIA-COLI RIBOSE BINDING-PROTEIN

Recently we reported (Yi et al., 1994) that the alpha a-helical conten t of the signal peptide of Escherichia coli ribose binding protein, wh en determined by circular dichroism (CD) and two-dimensional NMR in tr ifluoroethanol/water solvent, is higher than that of its nonfunctional mutant signal peptide. In the present investigation, the structures o f the signal peptides of two revertant ribose binding proteins in the same solvent were also determined with CD and two-dimensional H-1 NMR spectroscopy. According to the CD results, both of these revertant sig nal peptides showed an intermediate helicity between those of wild-typ e and mutant signal peptides, the helical content of the revertant pep tide with higher recovery of the translocation capability being higher . On the other hand, the alpha-helix regions of the wild-type and the revertant peptides as determined by NMR were shown to be the same. Thi s discrepancy may be due to the difference in stability between identi cal alpha-helical stretches in wild-type and revertant peptides, A goo d correlation was observed between the helical content of these four r ibose binding protein signal peptides in TFE/water as studied by CD an d their in vivo translocation activities. It appears, therefore, that both the proper length of the helix and the stability are of functiona l significance.