Conformational study of a new SGTx1 neurotoxin from the spider Scodra griseipes using mass spectrometry

SGTx1 is a new neurotoxin from the venom of Scodra griseipes. Because of th e small quantity of this natural peptide available, mass spectrometry was u sed to obtain information on its higher-order structure. The kinetics of re duction by 1,4-dithiothreitol (DTT) was monitored by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS), and s howed that one of the three disulfide bridges was appreciably more accessib le to the DTT. Studies based on the charge state distribution (CSD) and H/D exchange of the non-reduced peptide, under neutral and acidic conditions, were performed using electrospray mass spectrometry (ES-MS). In neutral sol ution, SGTx1 showed a maximum charge state of four compared with seven pote ntially protonated basic residues, and all labile hydrogens were exchanged. However, under acidic conditions, a maximum charge state of only five was observed, and four of the labile hydrogens could not be deuterated. These o bservations are interpreted in terms of a rigid structure maintained by the disulfide bridges, which can be temporarily relaxed by disulfide bridge sc rambling only at higher pH values. Copyright (C) 2001 John Wiley & Sons, Lt d.