Pressure-induced changes in the solution structure of the GB1 domain of protein G

The solution structure of the GB1 domain of protein G at a pressure of 2 kbar is presented. The structure was calculated as a change from an energy-minimised low-pressure structure using 1H chemical shifts. Two separate changes can be characterised: a compression/distortion, which is linear with pressure; and a stabilbation of an alternative folded state. On application of pressure, linear chemical shift changes reveal that the backbone structure changes by about 0.2 Å root mean square, and is compressed by about 1% overall. The α-helix compresses, particularly at the C-terminal end, and moves toward the β-sheet, while the β-sheet is twisted, with the corners closest to the α-helix curling up towards it. The largest changes in structure are along the second β-strand, which becomes more twisted. This strand is where the protein binds to IgG. Curved chemical shift changes with pressure indicate that high pressure also populates an alternative structure with a distortion towards the C-terminal end of the helix, which is likely to be caused by insertion of a water molecule. © 2007 Wiley-Liss, Inc.