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Gaucher disease, an autosomal recessive disorder, is caused by a deficiency of glucocerebrosidase (GCase) enzyme, a peripheral membrane-associated glycoprotein that hydrolyses glucosylceramide in lysosomes. Glycosylation is essential for the development of a catalytically active enzyme, specifically in the first site, located at Asn19. However, both the molecular basis of the relevance of N-glycosylation over GCase activity and the effects of glycosylation over its structure and dynamics are still not fully understood. Thus, the present work evaluated GCase enzyme in increasing glycosylation content using triplicate unbiased molecular dynamics simulations. Accordingly, the N-linked glycan chains caused local conformational stabilization effects over the protein, as well as in regions flanking the enzyme catalytic dyad. In the case of the Asn19-linked glycan, it also occurred around region 438-444, where one of the most prevalent GCase mutations is found. Markedly, an increasing catalytic dyad organization was related to increasing glycosylation contents, offering the first atomic-level explanation for the experimental observation that GCase activity is controlled by glycosylation, especially at Asn19.

Key Message: Human glucocerebrosidase with vacuolar anchoring domains was targeted to protein storage vacuoles (PSVs) of Arabidopsis seeds, but unexpectedly via the Golgi complex. PSV-targeting to effectively avoid problematic N-glycans is protein dependent. Plant-specific N-glycosylation patterns elaborated within the Golgi complex are a major limitation of using plants to produce biopharmaceuticals as the presence of β1,2 xylose and/or α1,3 fucose residues on the recombinant glycoprotein can render the product immunogenic if administrated parenterally. A reporter protein fused to a vacuolar membrane targeting motif comprised of the BP-80 transmembrane domain (TMD), and the cytoplasmic tail (CT) of α-tonoplast intrinsic protein (α-TIP) is delivered to protein storage vacuoles (PSVs) of tobacco seeds by ER-derived transport vesicles that bypass the Golgi complex. This prompted us to investigate whether a pharmaceutical glycoprotein is targeted to PSVs using the same targeting sequences, thus avoiding the unwanted plant-Golgi-specific complex N-glycan modifications. The human lysosomal acid β-glucosidase (glucocerebrosidase; GCase) (EC 3.2.1.45) fused to the BP-80 TMD and α-TIP CT was produced in Arabidopsis thaliana wild-type (Col-0) seeds. The chimeric GCase became localized in PSVs but transited through the Golgi complex, as indicated by biochemical analyses of the recombinant protein's N-glycans. Our findings suggest that use of this PSV-targeting strategy to avoid problematic N-glycan maturation on recombinant therapeutic proteins is not consistently effective, as it is likely protein- and/or species-specific.

The identification of hot spots, i.e., binding regions that contribute substantially to the free energy of ligand binding, is a critical step for structure-based drug design. Here we present the application of two fragment-based methods to the detection of hot spots for DJ-1 and glucocerebrosidase (GCase), targets for the development of therapeutics for Parkinson's and Gaucher's diseases, respectively. While the structures of these two proteins are known, binding information is lacking. In this study we employ the experimental multiple solvent crystal structures (MSCS) method and computational fragment mapping (FTMap) to identify regions suitable for the development of pharmacological chaperones for DJ-1 and GCase. Comparison of data derived via MSCS and FTMap also shows that FTMap, a computational method for the identification of fragment binding hot spots, is an accurate and robust alternative to the performance of expensive and difficult crystallographic experiments.

Gaucher disease is a lysosomal storage disorder caused by deficiency of human acid beta-glucosidase. Recent x-ray structural elucidation of the enzyme alone and in the presence of its inhibitor was done, which provided an excellent template for further studies on the binding of substrate, product and inhibitor. To draw correlations between the clinical manifestation of the disease driven by point mutations, L444P and L444R, and the placement and function of putative S-binding sites, the presented theoretical studies were undertaken, which comprised of molecular dynamics and molecular docking methods. The obtained results indicate the D443 and D445 residues as extremely important for physiological functionality of an enzyme. They also show, although indirectly, that binding of the substrate is influenced by an interplay of E235 and E334 residues, constituting putative substrate binding site, and the region flanked by D435 and D445 residues.