Structural elucidation of the PDI-related chaperone Wind with the help of mutants

The structures of the PDI-related protein Wind (with a C-terminal His(6) tag) and the mutants Y53S, Y53F and Y55K have been determined and compared with the wild-type structure with the His(6) tag at the N-terminus. All five structures show the same mode of dimerization, showing that this was not an artefact introduced by the nearby N-terminal His(6) tag and suggesting that this dimer may also be the biologically active form. Although the mutants Y53S and Y55K completely abrogate transport of the protein Pipe (which appears to be the primary function of Wind in the cell), only subtle differences can be seen in the putative Pipe-binding region. The Pipe binding in the active forms appears to involve hydrophobic interactions between aromatic systems, whereas the inactive mutants may be able to bind more strongly with the help of hydrogen bonds, which could disturb the delicate equilibrium required for effective Pipe transport.