Aggregation state of spin-labeled cecropin AD in solution. Biochemistry 1993 Nov 09;32(44):11895-902
Date
11/09/1993Pubmed ID
7692965DOI
10.1021/bi00095a019Scopus ID
2-s2.0-0027435124 (requires institutional sign-in at Scopus site) 35 CitationsAbstract
A spin-labeled derivative of the ion channel peptide cecropin AD (Fink et al., 1988) was synthesized and used to investigate its aggregation state in water and in the presence of a helix-promoting solvent. A cysteine was introduced at position 33 and spin-labeled using the methanethiosulfonate spin label. In low ionic strength aqueous solution, the peptide is monomeric, and the ESR spectrum indicates a high degree of segmental flexibility at the nitroxide attachment point, consistent with a predominantly random coil conformation. Upon addition of 5-10% (v/v) hexafluoro-2-propanol (HFP), the peptide is induced to aggregate as evidenced by significant motional restriction of the spin label and spin-spin broadening of the ESR lines. At higher concentrations of HFP, the peptide reverts to a monomeric state but retains its folded conformation. Our data suggest that between 5 and 10% HFP the peptide undergoes two structural transitions. The first transition starts at 5% and is very cooperative. Its dependence on ionic strength, temperature, and pH indicates that it involves the interconversion between a random coil and an ordered state stabilized by interpeptide electrostatic and hydrophobic interactions. The second transition, which occurs at 11% v/v HFP, is between the self-associated form and an ordered monomeric form. The analysis of our experimental results demonstrates aggregate formation at 5-10% HFP. This may be relevant to the mechanism of channel formation by cecropins in membranes.
Author List
Mchaourab HS, Hyde JS, Feix JBAuthor
Jimmy B. Feix PhD Emeritus Professor in the Biophysics department at Medical College of WisconsinMESH terms used to index this publication - Major topics in bold
Amino Acid SequenceChromatography, High Pressure Liquid
Cyclic N-Oxides
Cysteine
Electron Spin Resonance Spectroscopy
Hydrocarbons, Fluorinated
Indicators and Reagents
Insect Hormones
Insect Proteins
Ion Channels
Molecular Sequence Data
Propanols
Protein Binding
Protein Conformation
Protein Structure, Secondary
Solutions
Spin Labels
Thermodynamics
Urea
