Host–guest interactions in polycationic human serum albumin bioconjugates

Abstract

Polycationic human serum albumin, cHSA, as well as cHSA conjugates with multiple polyethylene(oxide) chains of two different lengths were synthesized, and the uptake and release of spin-labeled fatty acid (FA) ligands were quantitatively analyzed by continuous wave (CW) electron paramagnetic resonance (EPR) spectroscopy and nanoscale distance measurements with double electron–electron resonance (DEER) spectroscopy. It is found that the seven FA binding pockets of native HSA are less well accessible by FAs in cHSA and its PEO-conjugates. A large number (at least 25) of FAs can diffusely and electrostatically be bound to the surface of all highly cationic serum albumin variants. These bound FAs show a remarkable resilience against release from both cHSA and PEO conjugates. Conjugation of PEO chains to cHSA had only minute effects on all EPR data, indicating that PEO grafts can be used without reduction of effectiveness in the ligand binding.