Abstract
THE reports in this issue by Moore et a/. (on page 248) and in Science by Michnick et at.2 and Van Duyne et aP, of the structure of a small intracellular protein called FKBP, could help in the design of new immunosuppressive drugs, as well as in the unraveling of the mechanisms of cytoplasmic signalling in T lymphocytes.
The immunosuppressive drugs FK506, which binds to FKBP, and cyclosporin A, which binds to cyclophilin, are structurally unrelated but seem to have a similar mechanism of action involving this initial binding. Both cyclosporin A and FKBP are intracellular proteins with peptidyl-prolyl cis-trans isomerase activity which could either be fortuitous or be the essence of the immunosuppressive action. Rarely have such small proteins received so much attention the consequence is a plague of publications about them; more collaboration and less competition in this field would be a damn good thing.