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The Solution Structure of TRH—A 1H NMR Reinvestigation

✍ Scribed by T. Kanthimathi; L. Hughes; S. Subramanian

Publisher
John Wiley and Sons
Year
1996
Tongue
English
Weight
458 KB
Volume
34
Category
Article
ISSN
0749-1581

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✦ Synopsis

High-resolution 'H NMR and molecular mechanics calculations were used to evaluate the solution structure of TRH (pyroglutamic acid-histidine-prolinamide). The results indicate that there are only two rotamers present at room temperature with a sufficient energy barrier on the 400 MHz NMR time-scale to be well resolved. These are in the ratio of cu. 9: 1. A time-averaged single conformer was obtained when the NMR experiment was carried out at 90 "C. A two-dimensional COSY experiment further confirmed the presence of only two rotamers. Molecular mechanics calculations predict the presence of three rotamers, although statistically only two of them will be populated in the ratio of 9 5 : s at room temperature. Very little secondary structure was indicated from a 2D NOESY experiment and it is concluded that TRH adapts an extended and not a 'hairpin' structure. The 1 : 1 Li-TRH adduct also exhibits the presence of the same rotamers, although lithium binding is evidenced by a downfield shift of histidine NH resonances in both rotamers to the same extent of 80 Hz.

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