Enhancement of intrinsic fluorescence of human carbonic anhydrase II upon topiramate binding: Some evidence for drug-induced molecular contraction of the protein

In this report, the effect of topiramate (TPM), an anticonvulsant sulfamate drug, on the structure of human carbonic anhydrase II (hCA II) was investigated by spectroscopic techniques. The intrinsic fluorescence experiments indicated that TPM binding causes enhancement of enzyme fluorescence via decreasing the internal quenching and energy transfer efficiency, the result supported by molecular dynamics simulation. Thermodynamic analysis of the binding process suggested that hydrogen bonding and van der Waals interactions are the major forces in the interaction of TPM with hCA II. The far-UV circular dichroism (CD) results showed that TPM caused increment in α-helical and β-sheet content of hCA II whereas, near-UV CD experiments in the presence of the drug showed induction of some compactness in the enzyme tertiary structure. The number of accessible tryptophans and protein surface hydrophobicity index of the enzyme were reduced in the presence of TPM which confirms the enzyme structural compactness upon drug binding. In addition, the enzyme thermal stability was increased in the presence of the drug. It seems that the induction of compactness in the enzyme structure upon drug binding may be responsible for increment of its conformational stability.