Cyclophilins (CyPs) are a large class of highly conserved ubiquitous 
peptidyl-prolyl cis-trans isomerases. CyPs have also been identified as being a 
specific receptor for the immunosuppressive drug cyclosporin A and are involved 
in a variety of biological functions. CyPJ is a novel member of the CyP family 
and human CyPJ (hCyPJ) is the protein encoded by a cyclophilin-like gene from 
human foetal brain, which shows 50% sequence identity to human cyclophilin A 
(hCyPA). Recombinant hCyPJ was expressed in Escherichia coli and purified. The 
three-dimensional structure of hCyPJ has been determined by molecular 
replacement using the hCyPA structure as the search model and has been refined 
at 2.6 angstroms resolution. The hCyPJ molecule contains four helices and one 
beta-barrel composed of eight antiparallel beta-strands. The overall secondary 
and tertiary structures of hCyPJ are similar to those of hCyPA, but hCyPJ 
contains an additional disulfide bridge and four segments with conformations 
that are strikingly different from those of hCyPA. His43 and Gln52 of hCyPJ are 
expected to be the active sites based on sequence alignment with hCyPA. The 
hCyPJ structure shows a conserved water molecule close to His43 and Gln52 which 
appears to support the solvent-assisted mechanism.