Towards Engineering Hormone-binding Globulins as Drug Delivery Agents

Chan W, Zhou A and Read R., 9(11):e113402, PLoS One, 2014

This is a proof-of-concept study to exploit the mechanism of targeted release of cortisol by corticosteroid binding globulin (CBG) in order to carry therapeutic agents toward predetermined locations. They altered the reactive centre loop of CBG by site-directed mutagenesis to facilitate the cleavage by other proteases such as the prostate specific antigen (PSA, a prostate specific serine protease) and thrombin (a major protease in the blood coagulation cascade). They used fluorescence spectroscopy and biolayer interferometry (BLI) to investigate CBG-ligand interactions. The BLI approach was particularly useful when the fluorescence quenching experiments did not work due to mutation of Trp 371. The Trp 371 is the main source of intrinsic fluorescence in the CBG binding pocket. An Octet RED system (equipped with SA biosensors) was used to immobilize biotinylated cortisol. A serial dilution of CBG variants used for the KD determination revealed that the protein carrier binds to its ligand with a high affinity in the S-state. It is subjected to a larger decrease in binding affinity upon reactive centre-loop-cleavage in order to release much of the compound bound to the target site in the R-state.

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