3D 14 N/1 H Double Quantum/1 H Single Quantum Correlation Solid-State NMR for Probing the Parallel and Anti-Parallel Beta-Sheet Arrangement of Oligo-Peptides at Natural Abundance.

Abstract

The beta (β)-sheet structures of oligopeptides and polypeptides can be formed in anti-parallel (AP) and parallel (P) forms, which is an important feature to understand such structures. In principle, P- and AP-β-sheet structures can be identified by the presence (AP) or absence (P) of inter-strand 1 HNH /1 HNH correlations on a diagonal in the corresponding 2D 1 H double quantum (DQ)/1 H single quantum (SQ) spectrum due to the different inter-strand 1 HNH /1 HNH distances between the two arrangements. However, the 1 HNH /1 HNH peaks overlap with the 1 HNH3+ /1 HNH3+ peaks, which always give cross-peaks regardless of the β-sheet arrangement. The 1 HNH3+ /1 HNH3+ peaks disturb the observation of the presence/absence of 1 HNH /1 HNH correlations and the assignment of 1 HNH and 1 HNH3+ is not always available. Here, 3D 14 N/1 H DQ/1 H SQ correlation solid-state NMR experiments at fast magic angle spinning (70 kHz) are introduced to distinguish AP- and P-β-sheet structures. The 14 N dimension allows the distinction of 1 HNH /1 HNH peaks from 1 HNH3+ /1 HNH3+ peaks with clear assignments of 1 HNH and 1 HNH3+ . In addition, the high natural abundance of 1 H and 14 N enables 3D 14 N/1 H DQ/1 H SQ experiments of oligo-alanines (Ala3-6 ) in four hours without isotope labelling.