MUSIC, selective pulses, and tuned delays: amino acid type-selective (1)H-(15)N correlations, II

Amino acid type-selective experiments help to remove ambiguities in either manual or automated assignment procedures. Here we present modified triple-resonance experiments that yield amino acid type-selective (1)H-(15)N correlations. They are based on the MUSIC coherence transfer scheme which replaces the initial INEPT transfer and is selective for XH(2) or XH(3) (where X is either (15)N or (13)C). Signals of the desired amino acid types are thus selected based on the topology of the side chain. MUSIC is combined with selective pulses and carefully tuned delays to create experiments for Ser (S-HSQC); Val, Ile, and Ala (VIA-HSQC); Leu and Ala (LA-HSQC); Asp, Asn, and Gly (DNG-HSQC), as well as Glu, Gln, and Gly (EQG-HSQC). The new experiments are recorded as two-dimensional spectra and their performance is demonstrated by their application to two protein domains of 83 and 115 residues.