Nuclear magnetic resonance study of the solution structure of α1-purothionin. Sequential resonance assignment, secondary structure and low resolution tertiary structure

The solution structure of the 45-residue plant protein, α1-purothionin, is investigated by nuclear magnetic resonance (n.m.r.) spectroscopy. Using a combination of two-dimensional n.m.r. techniques to demonstrate through-bond and through-space (<5 Å) connectivities, the ¹H n.m.r. spectrum of α1-purothionin is assigned in a sequential manner. The secondary structure elements are then delineated on the basis of a qualitative interpretation of short-range nuclear Overhauser effects (NOE) involving the NH, CαH and CβH protons. There are two helices extending from residues 10 to 19 and 23 to 28, two short β-strands from residues 3 to 5 and 31 to 34 which form a mini anti-parallel β-sheet, and five turns. In addition, a number of long-range NOE connectivities are assigned and a low resolution tertiary structure is proposed.