Interconversion of the Specificities of Human Lysosomal Enzymes Associated with Fabry and Schindler Diseases

Scott C. Garman,Nathaniel E. Clark,Ivan B. Tomasic,Matthew C. Metcalf,Abigail I. Guce

doi:10.1074/jbc.m110.118588

Scott C. Garman, Nathaniel E. Clark + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m110.118588

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Abstract

The human lysosomal enzymes alpha-galactosidase (alpha-GAL, EC 3.2.1.22) and alpha-N-acetylgalactosaminidase (alpha-NAGAL, EC 3.2.1.49) share 46% amino acid sequence identity and have similar folds. The active sites of the two enzymes share 11 of 13 amino acids, differing only where they interact with the 2-position of the substrates. Using a rational protein engineering approach, we interconverted the enzymatic specificity of alpha- GAL and alpha-NAGAL. The engineered alpha-GAL (which we call alpha-GAL(SA)) retains the antigenicity of alpha-GAL but has acquired the enzymatic specificity of alpha-NAGAL. Conversely, the engineered alpha-NAGAL (which we call alpha-NAGAL(EL)) retains the antigenicity of alpha-NAGAL but has acquired the enzymatic specificity of the alpha-GAL enzyme. Comparison of the crystal structures of the designed enzyme alpha-GAL(SA) to the wild-type enzymes shows that active sites of alpha-GAL(SA) and alpha-NAGAL superimpose well, indicating success of the rational design. The designed enzymes might be useful as non-immunogenic alternatives in enzyme replacement therapy for treatment of lysosomal storage disorders such as Fabry disease.

Highlights

␣-GAL enzyme cleaves substrates containing terminal ␣-galactosides, including glycoproteins, glycolipids, and polysaccharides
SDS-PAGE analysis shows that the purified variant proteins migrate at the same size as their wild-type equivalents, ϳ50 kDa for ␣-GAL and ␣-GALSA and 52 kDa for ␣NAGAL and ␣-NAGALEL (Fig. 1D)
Insets show the active sites of ␣-GAL and ␣-NAGAL with their catalytic products ␣-galactose and ␣-GalNAc, respectively. 11 of the 13 active site residues are conserved between the enzymes, the overall sequence identity is 46%

Summary

EXPERIMENTAL PROCEDURES

Molecular Biology—Human ␣-GAL and human ␣-NAGAL were expressed in stably transfected Trichoplusia ni (Tn5) insect cells as described previously [10, 15]. The supernatant was clarified and concentrated by tangential flow filtration (Millipore Prep/ Scale) and exchanged into Ni2ϩ binding buffer (50 mM Na3PO4, pH 7.0, 250 mM NaCl, 20 mM imidazole, and 0.01% NaN3). 0.25–1.2 ␮g of enzyme in 10 ␮l of 100 mM citrate/phosphate buffer (pH 4.5) was added to 12 substrate concentrations (pNP-␣-Gal from 0.1 to 50 mM, and pNP-␣-GalNAc from 0.01 to 10 mM). Crystallization and X-ray Data Collection—Crystals of ␣-GALSA were grown as described for the D170A ␣-GAL variant [15]. Crystals were transferred stepwise into reservoir solution containing 200 mM ligand (GalNAc or galactose) and into cryoprotectant solution (15% polyethylene glycol 8,000, 0.1 M sodium cacodylate, pH 6.5, 22 mM Mg(CH3COO)2, 20% glycerol, and 200 mM ligand). Coordinates and structure factors are deposited in the Protein Data Bank under accession codes 3LX9, 3LXA, 3LXB, and 3LXC

RESULTS

Km mM

Data collection

DISCUSSION