¹H NMR study of robustoxin, the lethal neurotoxin from the funnel web spider Atrax robustus

Robustoxin, the lethal neurotoxin from the Sydney funnel web spider Atrax robustus, is a polypeptide of 42 residues cross-linked by four disulfide bonds. This paper describes the sequence-specific assignment of resonances in the ¹H nuclear magnetic resonance spectrum of robustoxin in aqueous solution. Several broad backbone amide resonances were encountered in spectra recorded at 27°C, making the assignments at that temperature incomplete. In spectra recorded at lower temperatures these amide resonances became sharper, but others that were sharp at 27°C became broad, indicative of conformational averaging on the millisecond timescale for certain regions of the structure. Nevertheless, it was possible to establish that robustoxin contains a small, triple-stranded, antiparallel β-sheet and several reverse turns, but no α-helix. These observations indicate that this toxin may adopt the inhibitor cystine knot structure found in polypeptides from a diverse range of species, including a number of spiders. Analysis of the pH dependence of the spectrum yielded pK(a) values for Tyr22 and Tyr25, one of the three carboxyl groups, and the Lys residues. Copyright (C) 1999 Elsevier Science Ltd.