The binding interaction of anticancer drug (using 5-fluorouracil (FU) as an example) with the model protein human serum albumin (HSA), and the FU-binding-induced microenvironment alterations in subdomain IIA of HSA molecule were studied by a combination of spectroscopic techniques and molecular docking method. The results indicated that the nature of forces involved in binding interaction between HSA and FU molecule were mainly van der Waal's forces and hydrogen bonding interactions. These interactions resulted in the formation of FU-HSA complex, making the local microenvironment in subdomain IIA of the protein more hydrophobic than its native state. Moreover, the interaction caused the large conformation changes of HSA, leading to the increase of the compact a-helix structures at low concentration of FU (less than 150 mu M). However, the high concentration of FU (higher than 150 mu M) made the compact a-helix structure decreasing, probably due to the protein undergoing some sort of distortion. Molecular docking study revealed that FU could enter the inside a hydrophobic cavity of subdomain IIA (Sudlow's site I) in proximity of Trp214 residue with the formation of specific hydrogen bonding with Trp214 and Lys199 residues, causing the fluorescence quenching of Trp214 through a static quenching mechanism. The study essentially provides an effective way for investigating the microenvironment alterations of protein induced by the drug molecules, and this approach can further be used in development of biomedicines and assessment of the safety-engineered drug delivery. (C) 2014 Elsevier Inc. All rights reserved.