NH resonances of Ribonuclease S‐peptide in aqueous solution. Low temperature n.m.r. study

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Abstract
A detailed study of the NH resonances of Ribonuclease-S-peptide (1-19 N-terminal fragment of Ribonuclease A) was carried out in H2O, pH 3.0, in the temperature range 1-31.degree. and ionic strength 0-1 M. Individual assignments of all NH amide signals were achieved by means of extensive double resonance experiments. The folding of S-peptide at low temperature was monitored by examination of several NH resonance parameters: 1st, the nonlinearity of chemical shift vs. temperature plots; 2nd, the selective broadening observed for signals assigned to residues 3-13; and 3rd, the decrease of 3JHNCH coupling constants belonging to this region of the polypeptide chain. All these results are in agreement with the formation of a folded structure at low temperature, which is similar to the one found for the S-peptide in the RNase S crystal.