MOLECULAR CHARACTERIZATION OF A CYCLOSPORINE-A INSENSITIVE CYCLOPHILIN FROM THE PARASITIC NEMATODE BRUGIA-MALAYI

The cyclophilins are a family of proteins that exhibit peptidyl-prolyl cis-trans isomerase (PPIase, EC 5.2.1.8) activity and bind the immuno suppressive agent cyclosporin A (CsA) to varying degrees. We have isol ated a cDNA clone encoding a novel cyclophilin from the human filarial parasite Brugia malayi. This gene possesses an N-terminal domain homo logous to cyclophilins from diverse phyla (49-60% amino acid sequence identity) and a hydrophilic C-terminal domain. The cyclophilin domain was overexpressed in Escherichia coli and found to possess peptidyl-pr olyl cis-trans isomerase (PPIase) activity, with a k(cat)/K-m value of 7.9 x 10(6) M(-1) s(-1). A histidine residue in lieu of tryptophan in the highly conserved CsA-binding site suggests that B. malayi cycloph ilin is more closely related to the cyclophilin-like proteins describe d recently from natural killer (NK) cells, plants, and the 40 kDa cycl ophilins from mammals. In accordance with the histidine-containing CsA -binding domain, the B. malayi enzyme was relatively insensitive to in hibition by CsA, since an IC50 value of 860 nM (compared to 19 nM for human cyclophilin A) was determined.