Binding study of novel anti-diabetic pyrimidine fused heterocycles to β-lactoglobulin as a carrier protein

Bovine milk β-lactoglobulin (β-LG) demonstrates significant resistance against both gastric- and simulated duodenal digestions. Therefore, it seems a realistic protein candidate for safe delivery and protection of particularly pH sensitive drugs in stomach. Recently, pyrimidine fused heterocycles (PFHs) revealed inhibitory properties against α-glucosidase (α-Gls) which is an important target enzyme for those drugs playing significant role in treatment of type-II diabetes and HIV/AIDS infection. The delivery of these compounds to small intestine where the enzyme plays its biological function is of great importance. Therefore, in this work the interaction of PFH compounds with β-LG, as a carrier protein has been investigated. Fluorescence, circular dichroism (CD) and UV–vis spectroscopic studies were used to examine the binding parameters and binding modes of the interaction. Moreover, the effects of PFH complexation on the secondary structures of β-LG were studied. All of these compounds significantly quenched the fluorescence intensity of β-LG due to a ground state complex formation. The binding and thermodynamic parameters were calculated. While hydrophobic interactions were proved to play significant role in the interaction of L1, L2 and L3, hydrogen bonding was shown to be important in the complexation of L4. The secondary structures of β-LG were preserved upon interaction of these synthetic compounds. Based on the achieved results, these potentially therapeutic agents can significantly bind to β-LG. Consequently, this protein might be useful for delivery of PFH compounds to small intestine where representing their potential ability to inhibit α-Gls and to reduce the postprandial hyperglycemia in diabetic patients.