Antigen: synthetic peptide corresponding to the residues of human FKBP52 · Clone designation: clone Hi52c · Host: mouse · Isotype: IgG1 · Application(s): IHC (paraffin embeded sections), IP, and WB · Hsp90 is crucial to cellular signaling by its regulation of the folding, activity, and stability of a wide range of client proteins. These client protein complexes may also contain one or more co-chaperones.¹ One class of Hsp90-binding co-chaperone is composed of proteins with a characteristic tetratricopeptide repeat (TPR) domain that forms an Hsp90 binding site. Among the TRP co-chaperones of Hsp90 are Hop/Sti1, protein phosphatase PP₅, and members of both the FK506- and cyclosporin A-binding families of immunophilins.² FK506-binding protein 51 (FKBP51) and FKBP52 are large molecular weight immunophilins that are part of the mature glucocorticoid receptor (GR) heterocomplex.³ The N-terminal domain of each protein binds FK506 and has peptidyl-prolyl isomerase (PPlase) activity that converts prolyl peptide bonds within target proteins from cis- to trans- proline. The C-terminal domains contain the TRP repeats involved in protein-protein interactions with Hsp40.⁴ Although FKBP52 and FKBP51 share ~75% sequence similarity, they affect hormone binding by the glucocorticoid receptor in opposing manners and have different Hsp90-binding characteristics.^3,5 Also, whereas FKBP51 typically has a role with the progesterone receptor, FKBP52 has been found to be linked to the progesterone, androgen, and glucocorticoid receptors.⁵

1 Cheung-Flynn, J., Roberts, P.J., Riggs, D.L., et al. C-terminal sequences outside the tetratricopeptide repeat domain of FKBP51 and FKBP52 cause differential binding to Hsp90. J Biol Chem 278(19) 17388-17394 (2003).

2 Davies, T.H., Ning, Y., Sánchez, E.R. A new first step in activation of steroid receptors. Hormone-induced switching of FKBP51 and FKBP52 immunophilins. J Biol Chem 277(7) 4597-4600 (2002).

3 Wu, B., Li, P., Liu, Y., et al. 3D structure of human FK506-binding protein 52: Implications for the assembly of the glucocorticoid receptor/Hsp90/immunophilin hetrocomplex. J Biol Chem 101(22) 8348-8353 (2004).

4 Denny, W.B., Prapapanich, V., Smith, D.F., et al. Structure-function analysis of squirrel monkey FK506-binding protein 51, a potent inhibitor of glucocorticoid receptor activity. Endocrinology 146(7) 3194-3201 (2005).

5 Cox, M.B., Riggs, D.L., Hessling, M., et al. FK506-binding protein 52 phosphorylation: A potential mechanism for regulating steroid hormone receptor activity. Mol Endocrinol 21(12) 2956-2967 (2007).

Davies, T.H., Ning, Y., Sánchez, E.R. A new first step in activation of steroid receptors. Hormone-induced switching of FKBP51 and FKBP52 immunophilins. J Biol Chem 277(7) 4597-4600 (2002).

Cheung-Flynn, J., Roberts, P.J., Riggs, D.L., et al. C-terminal sequences outside the tetratricopeptide repeat domain of FKBP51 and FKBP52 cause differential binding to Hsp90. J Biol Chem 278(19) 17388-17394 (2003).

Denny, W.B., Prapapanich, V., Smith, D.F., et al. Structure-function analysis of squirrel monkey FK506-binding protein 51, a potent inhibitor of glucocorticoid receptor activity. Endocrinology 146(7) 3194-3201 (2005).

Cox, M.B., Riggs, D.L., Hessling, M., et al. FK506-binding protein 52 phosphorylation: A potential mechanism for regulating steroid hormone receptor activity. Mol Endocrinol 21(12) 2956-2967 (2007).

Wu, B., Li, P., Liu, Y., et al. 3D structure of human FK506-binding protein 52: Implications for the assembly of the glucocorticoid receptor/Hsp90/immunophilin hetrocomplex. J Biol Chem 101(22) 8348-8353 (2004).

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