Structural studies of peptide hormone and signal sequence of escherichia coli ribose binding protein by NMR

Abstract

The structures of two peptide hormones, glucagon and luteinizing hormone releasing hormone, and functional and non-functional signal peptides of Escherichia coli ribose binding protein have been elucidated by detailed NMR and CD. The results are summarized below. (1) The structure of monomeric glucagon in dilute aqueous solution was studied by 500 MHz NMR. Hydrogen-deuterium exchange experiments monitored by NMR showed that the backbone amide NHs form intrastrand hydrogen bonds suggesting the existence of some degree of compact structure. The temperature dependent shift of several amide NH resonances supported the above conclusion. The small J coupling constants arising from the interactions between 6 amide NHs and C$\alpha$Hs(less than 6 Hz) implied a helical structure. (2) The NMR and CD studies on the structure of LHRH in water/TFE solution were performed at pH 3 and pH 7. At pH 3, no discernible structure was seen by CD measurement in the temperatures of 10$^\circ$C and 25$^\circ$C. But the evidences of the existence of a turn was obtained by NMR measurement at 10$\circ$C. At pH 5, and in more higher pH, the preference of $\beta$-structure was found. The effect of pH on the LHRH structure was discussed. In addition of $\beta$-structure, we could find out the characteristic NOEs of $\beta$-turn at pH 7. It seems that the antiparallel $\beta$-structure accompanying $\beta$-turn on the middle of sequence is unstable at low pH due to the ionization of His-2 residue. We suggest that the main structures of LHRH are $\beta$-turn and $\beta$-structure in water/TFE solution and there is an unusual turn rather than the random structure at low pH, water/TFE(1:1 by volume) solution. (3) The structures of chemically synthesized functional and non-functional signal peptides of Escherichia coli ribose binding protein were compared in the solvents which mimic the amphiphilic environments by CD and 2D 1H NMR. The functional peptide have a helix consisted of 19 residues star...