We are currently working on two MAS solid-state NMR methods aimed at determining of three-dimensional molecular structure and demonstrating them in the context of secondary structure determination in peptides. The experiments can be used in complementary fashion to determine the backbone torsion angles ~ and y. The first experiment measures the dipole coupling between two """"""""C carbonyl spin labels, which is a function of the ~ angle, affords the highest sensitivity at 1 20' 1 !~ 0 !~ 1 140' 1. The resolution of the experiment is enhanced by (i) using a y encoded pulse sequence of the C7-type to restore the 13C_13 C homonuclear dipole coupling and (ii) allowing the spin system to evolve under the dipolar interaction for relatively long times (ca. 40ms). In the second experiment, a double quantum state between two carbonyl """"""""C nuclei is simultaneously evolved for a variable time t, under both chemical shielding (CSA) interactions. The evolution profile depends on the relative orientation of the two """"""""C CSA tensors, which is primarily a function of the 0 and V torsion angles. The experiment can be performed at relatively high spinning rates (co/27c - 10 kHz), using with double quantum filtration to suppress the natural abundance """"""""C signals. Numerical simulations indicate good sensitivity and resolution for 0 and xV in many of the biologically interesting regions (experiment has a particularly large dynamic range for torsion angles commonly observed in helical peptides and proteins). Both experiments can be carried out on a peptide specifically 13C labeled at the carbonyl positions of two adjacent'amino acid residues. In our studies, we employed tripeptide L-Ala-L-Gly-L-Gly with labels at Ala- 1 and Gly-2.

Agency
National Institute of Health (NIH)
Institute
National Center for Research Resources (NCRR)
Type
Biotechnology Resource Grants (P41)
Project #
5P41RR000995-26
Application #
6449581
Study Section
Project Start
2001-05-01
Project End
2002-04-30
Budget Start
Budget End
Support Year
26
Fiscal Year
2001
Total Cost
Indirect Cost
Name
Massachusetts Institute of Technology
Department
Type
DUNS #
City
Cambridge
State
MA
Country
United States
Zip Code
02139
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