# Membrane Channel Forming Polypeptides. 270-MHz Hydrogen-1 Nuclear Magnetic Resonance Studies on the Conformation of the 11-21 Fragment of Suzukacillin

Iqbal, M and Balaram, P (1981) Membrane Channel Forming Polypeptides. 270-MHz Hydrogen-1 Nuclear Magnetic Resonance Studies on the Conformation of the 11-21 Fragment of Suzukacillin. In: Biochemistry, 20 (17). pp. 4866-4871.

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270-MHz 1H NMR studies on the synthetic suzukacillin fragments Boc-Leu-Aib-Gly-Leu-Aib-OMe (13-17), Boc-Gln-Aib-Leu-Aib-Gly-Leu-Aib-OBz (11-17), Boc-Leu-Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (13-21), and Boc-Gln-Aib-Leu- Aib-Gly-Leu-Aib-Pro-Val-Aib-Aib-OMe (11-21) have been carried out in $CD{Cl}_3$ and ${({CD}_3)}_2SO$. The intramolecularly hydrogen-bonded amide hydrogens in these peptides have been identified by using solvent titration experiments and temperature coefficients of NH chemical shifts in ${({CD}_3)}_2SO$. The peptides are shown to favor conformations stabilized by intramolecular 4 \rightarrow 1 hydrogen bonds. The 11-21 fragment adopts a highly folded, largely $3_{10}$ helical conformation stabilized by seven intramolecular hydrogen bonds. An eighth NH group [Gly(5)] appears to be involved in a weaker interaction. Evidence for the possible participation of the Gln side-chain carboxamide group in hydrogen bonding to the peptide backbone is also presented.