Cañadas, OSáenz, AOrellana Moraleda, GuillermoCasals Carro, María Cristina2024-01-152024-01-152005-05-01Cañadas O, Sáenz A, Orellana G, Casals C. Equilibrium studies of a fluorescent tacrolimus binding to surfactant protein A. Anal. Biochem. 2005 May 1; 340(1): 57-65. 20050003-269710.1016/j.ab.2005.01.056https://hdl.handle.net/20.500.14352/93041Tacrolimus (FK506) is a hydrophobic immunosuppressive agent used in kidney, liver, and lung transplantation. The objective of this study was to characterize the binding of FK506 to surfactant protein A (SP-A), an abundant lipoprotein found in the alveolar fluid that functions as part of the innate immune system in the lung. We have synthesized a novel derivative of FK506 in which a dansyl moiety was covalently bound via cadaverine to the C22 position of the FK506 molecule (DNS-FK). Using the fluorescence and anisotropy properties of DNS-FK, we demonstrated that tacrolimus avidly binds to SP-A with an apparent equilibrium association constant (K(app)) of 10(7)M(-1) and a Gibbs binding free energy of -40 kJ mol(-1)K(-1). Derivatization of FK506 at the C22 position did not block FK506 binding to the cytosolic immunophilin FK506-binding protein (FK-BP) or human serum albumin (HSA), both used as controls of tacrolimus-binding proteins. K(app) for FK-BP/DNS-FK and HSA/DNS-FK complexes were 1.5 x 10(7) and 10(7)M(-1), respectively. The high sensitivity of this analytical technique makes it suitable for binding analysis of FK506 to proteinsengAttribution-NoDerivatives 4.0 Internationaljournal articleopen access547577.1Fluorescent tacrolimusDansylcadaverine-FK506SP-AFK506 binding proteinHuman serum albuminFluorescence anisotropy assayCiencias23 Química24 Ciencias de la Vida