Structural basis of pharmacological chaperoning for human {beta}-galactosidase [Enzymology]

April 15th, 2014 by Suzuki, H., Ohto, U., Higaki, K., Mena-Barragan, T., Aguilar-Moncayo, M., Mellet, C. O., Nanba, E., M. Garcia Fernandez, J., Suzuki, Y., Shimizu, T.

GM1 gangliosidosis and Morquio B disease are autosomal recessive diseases caused by the defect in the lysosomal β-galactosidase (β-Gal), frequently related to misfolding and subsequent endoplasmic reticulum-associated degradation (ERAD). Pharmacological chaperone (PC) therapy is a newly developed molecular therapeutic approach by using small molecule ligands of the mutant enzyme that are able to promote the correct folding, prevent ERAD and promote trafficking to the lysosome. In this report, we describe the enzymological properties of purified recombinant human β-GalWT and two representative mutants in GM1 gangliosidosis Japanese patients, β-GalR201C and β-GalI51T. We have also evaluated the PC effect of two competitive inhibitors of β-Gal. Moreover, we provide detailed atomic view of the recognition mechanism of these compounds in comparison with two structurally related analogues. All compounds bind to the active site of β-Gal with the sugar moiety making hydrogen bonds to active site residues. Moreover, the binding affinity, the enzyme selectivity and the PC potential are strongly affected by the mono or bicyclic structure of the core as well as the orientation, the nature and the length of the exocyclic substituent. These results provide understanding on the mechanism of action of β-Gal selective chaperoning by newly developed PC compounds.