Conformational study of a somatostatin analogue in DMSO/water by 2D NMR

✍ Scribed by Patricia Verheyden; Wim Francq; Henri Pepermans; Georges Van Binst

• Publisher: Wiley (John Wiley & Sons)
• Year: 1990
• Tongue: English
• Weight: 470 KB
• Volume: 30
• Category: Article
• ISSN: 0006-3525
• DOI: 10.1002/bip.360300720

✦ Synopsis

NMH studies of numerous somatostatin analogues have shown that all those showing biological activity adopt a o,, I turn-6 sheet conformation in dimethylsulfoxide (DMSO ) solution, but that this is not a sufficient condition for biological

In this communication, we demonstrate that this backbone conformation is conserved in different solvents, and, consequently, we postulate that this conformation might be adopted at the receptor also.

We performed this study on the analogue DC13-116 ( ~~Nal~-Cys~-Tyr~-DTrp~-Lys~-Val'~-Cys "-Thr "-NHz, numbering as in native somatostatin), a highly active somatostat in analogue in the GH release inhibitory This analogue is expected t o have a constrained conformation due to its reduced sizeg ( 8 amino acids out of 14 in native somatostatin), the cyclization between the two cysteins,"' and the replacement of LTrp in position 8 by 1)Trp."

Measurements done previously by our group on DC13-11 6 in water solution' indicated a different conformation. This conformation proposal was based mainly on measurements of the temperature dependence of the chemical shifts of the amide protons ( A 6 N H / A T measurements), which contained a systematic error, due to the temperature shift of' the reference signal. T h e lack of reliable NOE data in water did not allow us at that time t o check our interpretation thoroughly. Subsequent ROESY experiments in water yielded sequential doN NOE's,'' which suggested the conservation of the backbone conformation from DMSO to H20. In order to further substantiate the independence of the conformation on the hydrophobicity of the solvents, we decided to study this somatostatin analogue in a mixture DMSOIH20 that is claimed t o have dipolar properties very similar to water.l3.l4 This mixture has a viscosity at least as high as pure DMSO. Thus we expected to observe more NOE's and obtain enough parameters to define unambiguously the backbone conformation. In addition, because of its low melting point (235