Conformational studies on synthetic peptides reproducing the dibasic processing site of pro‐ocytocin–neurophysin

Abstract

Synthetic peptides reproducing the proteolytic processing site of pro-ocytocin were studied by different spectroscopic techniques, including circular dichroism, Fourier transform infrared absorption, and mono and bidimensional nuclear magnetic resonance, in order to ascertain the possible role of three-dimensional structure in the recognition process by maturation enzymes. Experimental results were compared with energy minimization calculations and suggest that: (i) the region situated on the N-terminus of the Lys-Arg doublet may form a beta-turn; (ii) the sequential organization of the residues participating in the beta-turn determines the privileged relative orientation of the basic amino acid sidechains and the subtype of turn; and (iii) the peptide segment situated on the C-terminal side of the dibasic doublet may assume a helix arrangement. These findings, in spite of the limitations connected to the flexibility of linear peptides, seem to substantiate the hypothesis that structural motifs around the cleavage site could be important for recognition and processing. however, a straightforward correlation between details of the secondary structure and the in vitro reactivity toward a putative convertase is not yet possible.

A conformational study in solution of pro-somatostatin fragments by NMR and computational methods

“…The i-turn motif seems, then, a quite general motif for those prohormone molecules where cleavage occurs in the proximity of a dibasic Arg-Lys pair. This has already been suggested in the case of pro-ocytocin fragments [4,5] and is confirmed again in the present study.…”

“…In recent years numerous studies have been made on the characterization of the structural parameters that are thought to play a key role in the enzymeprohormone recognition process [1][2][3][4][5].…”

Expression, Folding, and Thermodynamic Properties of the Bovine Oxytocin−Neurophysin Precursor: Relationships to the Intermolecular Oxytocin−Neurophysin Complex

“…The assumption that this new unbound state has the same stability to denaturation as unliganded mature NP leads to the results presented here. Relevant in this context is the fact that modeling studies have suggested conformational differences between the internally bound state of the bovine oxytocin precursor and the corresponding processed complex (38), and that structural studies of synthetic peptides representing the first 20 residues of the bovine oxytocin precursor suggest an influence of the GlyLys-Arg linker sequence on local structure in this region (39,40). The low effective intramolecular concentration of oxytocin within the precursor indicates that the internal free energy cost associated with bringing oxytocin and NP together approaches in magnitude the translational and rotational entropy loss associated with the bimolecular reaction and/ or that some of the secondary interactions (those not involving the hormone amino group or tyrosine) between oxytocin and NP in the intermolecular complex (6) are absent in the precursor.…”

New Fourier transform infrared based computational method for peptide secondary structure determination. I. Description of method

“…Preliminary FTIR experiments performed in our laboratories with synthetic fragments, representing the processing site of proocytocin–neurophysin (pro‐OT/Np), in the presence of solvents unable to donate protons, such as dimethylsulfoxide (DMSO),22 indicated that H → D substitution on the amide function of peptide groups induces modifications of both the position and the intensity of the amide I band. The effects of the isotopic substitution were observed in the 1710–1670 and 1670–1650 cm −1 regions, which are attributable to α‐turns and β‐helices, respectively.…”