Hello Eleanor,
We found some intermolecular vicinal disulfides recently that we think are 'real'. This class of proteins forms tetramers and in one version we find these intermolecular disulfides across molecules. We did some tests and found that oxidation or reduction
has an effect on the stability of the protein. We also saw this was consistent across multiple space groups. If you would like to have a look, they were just released: 5HY0, 5HY2, 5HY4.
As a comparison to another protein in this fold class that doesn't have the disulfide is 5HWE.
cheers, tom