A new strategy for sequential assignment of intrinsically unstructured proteins based on 15N single isotope labelling

We describe a new efficient strategy for the sequential assignment of amide resonances of a conventional N-15-H-1 HSQC spectrum of intrinsically unfolded proteins, based on composite NOESY-TOCSY and TOCSY-NOESY mixing times. These composite mixing times lead to a Hoc-proton mediated unidirectional transfer of amide to amide proton. We have implemented the composite mixing times in an HSQC-NOESY-HSQC manner to obtain directional connectivity between amides of neighbouring residues. We experimentally determine the optimal mixing times for both transfer schemes, and demonstrate its use in the assignment for both a fragment of the neuronal tau protein and for alpha-synuclein. (C) 2013 Elsevier Inc. All rights reserved.