Conformation and EPR characterization of rigid, 310 -helical peptides with TOAC spin labels: Models for short distances.
For 3D-structure determination in biophysical systems EPR is rapidly gaining ground. Proteins labeled specifically with two nitroxide spin labels can be prepared, and several EPR methods are available for distance determination, which makes it possible to determine distance constraints. However, such methods require frozen solutions, potentially causing non-physiological states of the sample. Here, we target spin- spin interaction in liquid solution at room temperature using rigid model compounds. A series of 310 -helical peptides, based on α-aminoisobutyric acid (Aib), is synthesized with pairs of spin labels separated by three, four, and five amino acids. To avoid flexibility, the noncoded nitroxyl-containing α-amino acid TOAC that is rigidly connected with the peptide backbone, is used. The EPR spectra of the peptides show a decreasing amount of coupling between the two spin labels within this series. We suggest through-bond interaction as the dominating mechanism for exchange interaction (J) and find a stronger J-coupling than in the corresponding Ala-based TOAC-peptides investigated previously (Hanson, et al., J Am Chem Soc 1996, 118, 7618-7625). We speculate that stronger coupling in Aib- vs Ala- peptides is due to intrinsically stronger through-bond interaction in the Aib-based peptides.
Department of Molecular Physics, Huygens Laboratory, Leiden University, 2300, RA Leiden, The Netherlands.
Maryam Hashemi
MH
Shabestari
Martin
M
van Son
Alessandro
A
Moretto
Marco
M
Crisma
Claudio
C
Toniolo
Martina
M
Huber
D003198:Computer Simulation; D003497:Cyclic N-Oxides / Q000737:chemistry*; D004578:Electron Spin Resonance Spectroscopy; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry*; D017433:Protein Structure, Secondary; D013113:Spin Labels
D003497:Cyclic N-Oxides; D010455:Peptides; D013113:Spin Labels; C037109:2,2,6,6-tetramethylpiperidine-N-oxide-4-amino-4-carboxylic acid
Cα-tetrasubstituted α-amino acids; IR absorption; TOAC; electron paramagnetic resonance; peptide conformation