The mammalian heat shock protein binding immunophilin (p59/HBI) is an ATP and GTP binding protein.

A protein of M(r) 59,000 (p59) was recently cloned and identified as a Heat shock protein Binding Immunophilin (p59/HBI). It participates to the heterooligomeric, non-DNA binding form of steroid receptors, in association with the heat shock protein of M(r) 90,000 (hsp90). It binds the immunosuppressants FK506 and rapamycin and possesses three FKBP-12 (FK506 binding protein of M(r) 12,000)--like domains (I to III), plus a tail containing a putative calmodulin binding site (domain IV). Following expression in E. Coli and purification on Glutathione-Sepharose of either the full-length recombinant p59/HBI, or the recombinant FKBP-like domains, we demonstrate by autoradiography of [alpha 32P]-8-azido ATP and of [alpha 32P]-8-azido GTP photoaffinity labeled complexes, that an ATP (GTP) binding site is located in the domain II. This nucleotide binding property is also found with the highly purified rabbit uterus p59/HBI. The latter, but not the recombinant protein, can be phosphorylated in vitro in the presence of Mn++ and/or of Ca++/Calmodulin in an ATP but not GTP dependent manner, suggesting copurification of a CaM kinase II-like enzyme. Thus it appears that p59/HBI is a multifunctional immunophilin which may be at the crossroad of the endocrine and immunological systems.