NMR studies of adrenocorticotropin hormone peptides in sodium dodecylsulfate and dodecylphosphocholine micelles: Proline isomerism and interactions of the peptides with micelles

Three adrenocorticotropin hormone (ACTH) fragments (1-10, 1-24, and 11-24) have been studied in water and in sodium dodecylsulfate (SDS) and dodecylph osphocholine (DPC) micelles by nuclear magnetic resonance spectroscopy. The trans-cis isomerism at all three proline sites (at positions 12, 19, and 2 4) was found in the 11-24 segment of the peptide. The population of the cis isomers changes with the environment of the peptide. Specifically, the pre sence of the DPC micelle does not affect the trans-cis equilibrium in the 1 1-24 segment from that in water. In contrast, the presence of the SDS micel les decreases the population of the cis isomer at Pro(24), but increases it s population at Pro(12) and Pro(19). The effect of SDS micelles on the tran s-cis equilibrium at these proline sites was discussed. Intermolecular nucl ear Overhauser effect (NOE) correlations between the ACTH peptides and the micelles were observed. These correlations occurred only in the 1-10 segmen t of the peptides, and the hydrophobic side chains contributed most to the intermolecular NOE. The intermolecular NOE pattern corroborates the suggest ion that the 1-10 segment of the ACTH peptides bind to these micelles via a surface-binding mode, with most of the interactions coming from the insert ion of the hydrophobic side chains. (C) 2000 John Wiley & Sons, Inc.