Direct detection of lysine side chain NH3+ in protein-heparin complexes using NMR spectroscopy.

Two NMR observables, the NζH3+ peak in the HISQC spectrum and Nζ chemical shift difference between the free and heparin-bound forms, can identify binding-interface lysines in protein-heparin complexes. Unlike backbone chemical shifts, these direct probes are stringent and are less prone to either false positives or false negatives.