Characterization of recombinant alpha-galactosidase for use in seroconversion from blood group B to O of human erythrocytes

Biopharmaceutical applications of α-galactosidases

α-Galactosidases are exoglycosidases that are active on galactose-containing side chains in oligosaccharides, polysaccharides, glycolipids, and glycoproteins. α-Galactosidases are gaining increased interest in human medicine, especially in the enzyme replacement therapy for Fabry's disease. α-Galactosidases with regioselectivity toward α-1,3-linked galactose find application in xenotransplantation and blood group transformation. The use of α-galactosidases as a therapeutic agent in alleviating the postprandial symptoms of irritable bowel syndrome is much acclaimed. The excellent therapeutic applications of α-galactosidases have led to an upwelling of worldwide research interventions to identify novel α-galactosidases with improved catalytic efficiency. In addition to these therapeutic applications, α-galactosidases also have interesting applications in the industrial sectors like food, feed, probiotics, sugar, and paper pulp. The current review focuses on the diverse therapeutic applications of α-galactosidases and their prospects.

Tolerability to non-endosomal, micron-scale cell penetration probed with magnetic particles

The capability of HeLa cells to internalize large spherical microparticles has been evaluated by using inorganic, magnetic microparticles of 1 and 2.8 µm of diameter. In both absence but especially under the action of a magnet, both types of particles were uptaken, in absence of cytotoxicity, by a significant percentage of cells, in a non-endosomal process clearly favored by the magnetic field. The engulfed particles efficiently drive inside the cells chemically associated proteins such as GFP and human alpha-galactosidase A, without any apparent loss of protein functionalities. While 1 µm particles are completely engulfed, at least a fraction of 2.8 µm particles remain embedded into the cell membrane, with only a fraction of their surface in cytoplasmic contact. The detected tolerance to endosomal-independent cell penetration of microscale objects is not then restricted to organic, soft materials (such as bacterial inclusion bodies) as previously described, but it is a more general phenomenon also applicable to inorganic materials. In this scenario, the use of magnetic particles in combination with external magnetic fields can represent a significant improvement in the internalization efficiency of such agents optimized as drug carriers. This fact offers a wide potential in the design and engineering of novel particulate vehicles for therapeutic, diagnostic and theragnostic applications.

Enzymatic Conversion of RBCs by α-N-Acetylgalactosaminidase from Spirosoma linguale

Spirosoma linguale is a free-living nonpathogenic organism. Like many other bacteria, S. linguale produces a cell-associated α-N-acetylgalactosaminidase. This work was undertaken to elucidate the nature of this activity. The recombinant enzyme was produced, purified, and examined for biochemical attributes. The purified enzyme was ~50 kDa active as a homodimer in solution. It catalyzed hydrolysis of α-N-acetylgalactosamine at pH 7. Calculated K_M was 1.1 mM with k_cat of 173 s⁻¹. The described enzyme belongs to the GH109 family.

Enhancement of red blood cell transfusion compatibility using CRISPR-mediated erythroblast gene editing

Regular blood transfusion is the cornerstone of care for patients with red blood cell (RBC) disorders such as thalassaemia or sickle‐cell disease. With repeated transfusion, alloimmunisation often occurs due to incompatibility at the level of minor blood group antigens. We use CRISPR‐mediated genome editing of an immortalised human erythroblast cell line (BEL‐A) to generate multiple enucleation competent cell lines deficient in individual blood groups. Edits are combined to generate a single cell line deficient in multiple antigens responsible for the most common transfusion incompatibilities: ABO (Bombay phenotype), Rh (Rh_null), Kell (K₀), Duffy (Fy_null), GPB (S−s−U−). These cells can be differentiated to generate deformable reticulocytes, illustrating the capacity for coexistence of multiple rare blood group antigen null phenotypes. This study provides the first proof‐of‐principle demonstration of combinatorial CRISPR‐mediated blood group gene editing to generate customisable or multi‐compatible RBCs for diagnostic reagents or recipients with complicated matching requirements.

Red Cell Immunohematology Research Conducted in China

ABO subtypes and RhD variants are the most studied blood groups in China. Some of the polymorphisms in these two blood groups have direct clinical relevance. Molecular diagnosis of blood group polymorphisms is underway in China. In addition, research groups have developed methods such as screening for blood group mimetic peptides using phage display technology. New reagents, akin to antibodies directed against RhD and ABO, are being investigated using aptamer-based techniques. Progress is also being made in the development of synthetic exoglycosidases for conversion of group A and/or B antigens to group O. Development of methoxy-polyethylene-glycol modified red cells has been successful in vitro but has not reached clinical application. In this paper, we summarize red cell immunohematology research that has been conducted in China.

Hooked on α-d-galactosidases: from biomedicine to enzymatic synthesis

α-d-Galactosidases (EC 3.2.1.22) are enzymes employed in a number of useful bio-based applications. We have depicted a comprehensive general survey of α-d-galactosidases from different origin with special emphasis on marine example(s). The structures of natural α-galactosyl containing compounds are described. In addition to 3D structures and mechanisms of action of α-d-galactosidases, different sources, natural function and genetic regulation are also covered. Finally, hydrolytic and synthetic exploitations as free or immobilized biocatalysts are reviewed. Interest in the synthetic aspects during the next years is anticipated for access to important small molecules by green technology with an emphasis on alternative selectivity of this class of enzymes from different sources.

Evaluation of group A1B erythrocytes converted to type as group O: studies of markers of function and compatibility

BACKGROUND

Enzymatic conversion of blood group A1B red blood cells (RBC) to group O RBC (ECO) was achieved by combined treatment with α-galactosidase and α-N-acetylgalactosaminidase. The aim of this study was to evaluate the function and safety of these A1B-ECO RBC in vitro.

MATERIALS AND METHODS

A 20% packed volume of A1B RBC was treated with enzymes in 250 mM glycine buffer, pH 6.8. The efficiency of the conversion of A and B antigen was evaluated by traditional typing in test tubes, gel column agglutination technology and fluorescence-activated cell sorting (FACS) analysis. The physiological and metabolic parameters of native and ECO RBC were compared, including osmotic fragility, erythrocyte deformation index, levels of 2,3-diphosphoglycerate, ATP, methaemoglobin, free Na(+), and free K(+). The morphology of native and ECO RBC was observed by scanning electron microscopy. Residual α-galactosidase or α-N-acetylgalactosaminidase in A1B-ECO RBC was detected by double-antibody sandwich ELISA method. Manual cross-matching was applied to ensure blood compatibility.

RESULTS

The RBC agglutination tests and FACS results showed that A1B RBC were efficiently converted to O RBC. Functional analysis suggested that the conversion process had little impact on the physiological and metabolic parameters of the RBC. The residual amounts of either α-galactosidase or α-N-acetylgalactosaminidase in the A1B-ECO RBC were less than 10 ng/mL of packed RBC. About 18% of group B and 55% of group O sera reacted with the A1B-ECO RBC in a sensitive gel column cross-matching test.

DISCUSSION

The conversion process does not appear to affect the morphological, physiological or metabolic parameters of A1B-ECO RBC. However, the A1B-ECO RBC still reacted with some antigens. More research on group O and B sera, which may partly reflect the complexity of group A1 the safety of A1B-ECO RBC is necessary before the application of these RBC in clinical transfusion.

The effect of treatment with α-glycosidases from Bacteroides fragilis on the survival of rat erythrocytes in the circulation

BACKGROUND

It has been demonstrated recently that α1,3-galactosidase from Bacteroides fragilis can efficiently convert human group B red blood cells (RBC) to group O cells. In addition, in vitro data indicated that the enzymatic conversion process did not affect the physiological or metabolic parameters of the RBC. The aim of this study was to investigate the lifespan of enzyme- treated RBC in vivo in the circulation.

MATERIALS AND METHODS

This was an experimental, randomised study. The rat was selected as the experimental subject because it expresses α-1,3galactosyl on its RBC. The efficiency of Galα1,3Gal epitope removal from RBC treated with α1,3-galactosidase was tested before the transfusion experiment to track the survival of RBC in the circulation. The animals were divided into three groups and injected via the tail vein with native, mock-treated or enzyme-treated RBC labelled with fluorescein isothiocyanate. The survival rates of the fluorescently labelled RBC were monitored by flow cytometry.

RESULTS

Flow cytometry showed that α-galactosidase (0.02 mg/mL for RBC with a haematocrit of 30%) efficiently removed Galα1,3Gal epitopes from rat erythrocytes, although small amounts of remaining Galα1,3Gal epitopes were still detected. The in vivo data demonstrated that the half-life of enzyme-treated RBC was a little shorter than that of native RBC. However, the 24-hour survival fractions of native, mock-treated and enzyme-treated RBC were virtually identical. Most importantly, the enzyme-treated RBC, like the native RBC, were still detectable 35 days after transfusion.

DISCUSSION

Our results indicate that α-glycosidase treatment had little effect on the in vivo survival kinetics of RBC. These data add further support to the feasibility of translating enzymatic conversion technology into clinical practice.

Silencing red blood cell recognition toward Anti-A antibody by means of polyelectrolyte layer-by-layer assembly in a two-dimensional model system

Silencing the antigenic response of red blood cells (RBCs) is a prerequisite toward the development of universal blood transfusion. Using a two-dimensional (2D) model whereby nonfixed RBCs are adsorbed on a human fibronectin (HFN)-coated surface, we demonstrate that the layer-by-layer (LbL) assembly technique of biocompatible polyelectrolytes can be employed to achieve the immunocamouflage of RBCs against the Anti-A antibody while maintaining the integrity and viability of the cells. The multilayered film consisted of a protecting shell (P-shell), containing five bilayers of chitosan-graft-phosphorylcholine (CH-PC) and sodium hyaluronate (HA), covered by a camouflage shell (C-shell) made up of five bilayers of poly-(L-lysine)-graft-poly(ethylene glycol) (PLL-PEG) and alginate (AL). Control experiments in which RBCs were coated by (CH-PC/HA)(10) bilayers indicated that the two polyelectrolytes alone did not prevent immunorecognition. The LbL film formation on RBCs and model substrates was monitored by quartz crystal microbalance with dissipation factor (QCM-D) and analyzed through zeta-potential measurements, atomic force microscopy (AFM), and optical microscopy. Antibody interaction with the coated RBCs was investigated by QCM-D, fluorescence microscopy, and hemolysis assays. Results from these measurements demonstrated that the hybrid LbL system built-up with different sets of polyelectrolytes was able to protect the RBCs from hemolysis and recognition by the Anti-A antibody.

The Galalpha1,3Galbeta1,4GlcNAc-R (alpha-Gal) epitope: a carbohydrate of unique evolution and clinical relevance

In 1985, we reported that a naturally occurring human antibody (anti-Gal), produced as the most abundant antibody (1% of immunoglobulins) throughout the life of all individuals, recognizes a carbohydrate epitope Galalpha1-3Galbeta1-4GlcNAc-R (the alpha-gal epitope). Since that time, an extensive literature has developed on discoveries related to the alpha-gal epitope and the anti-Gal antibody, including the barrier they form in xenotransplantation and their reciprocity in mammalian evolution. This review covers these topics and new avenues of clinical importance related to this unique antigen/antibody system (alpha-gal epitope/anti-Gal) in improving the efficacy of viral vaccines and in immunotherapy against cancer.

Modulating the red cell membrane to produce universal/stealth donor red cells suitable for transfusion

Two approaches have been used to produce universal group O donor red blood cells (RBCs) from groups A, B, and AB RBCs. The first involves cleavage of the terminal immunodominant sugars from carbohydrate chains on the RBC membrane, using specific enzymes, to produce so-called enzyme-converted group O (ECO) RBCs. ECO RBCs have been produced from whole units of B RBCs and transfused successfully to humans. Group A RBCs (especially A(1) RBCs) have been more difficult. New sources of enzymes have produced ECO RBCs from A(1) and A(2) RBCs that do not react with powerful monoclonal anti-A. Unfortunately, there are still problems encountered with polyclonal human antibodies (i.e. cross-matching). The second approach interferes with an antibody reaching its specific antigen on the RBC membrane by bonding polyethylene glycol (PEG) to the RBC. PEG will attract water molecules, yielding a combination that may block most RBC antigens, including A and B antigens. Initial excitement generated by preliminary reports of the possibility of producing 'stealth' PEG-RBCs were tempered by the findings of in vitro serological problems and possible reduced in vivo RBC survival. Many of these problems were solved, but recent findings that PEG is immunogenic in animals and humans, and that PEG antibodies can shorten the survival of PEG-RBCs (in rabbits) and pegylated proteins (e.g. PEG-asparaginase) in humans, are disturbing, suggesting that 'stealth' RBCs may never become a reality.

Modifying the red cell surface: towards an ABO-universal blood supply

Eliminating the risk for ABO-incompatible transfusion errors and simplifying logistics by creating a universal blood inventory is a challenging idea. Goldstein and co-workers pioneered the field of enzymatic conversion of blood group A and B red blood cells (RBCs) to O (ECO). Using alpha-galactosidase from coffee beans to produce B-ECO RBCs, proof of principle for this revolutionary concept was achieved in clinical trials. However, because this enzyme has poor kinetic properties and low pH optimum the process was not economically viable. Conversion of group A RBCs was only achieved with the weak A2 subgroup with related enzymes having acidic pH optima. More recently, the identification of entirely new families of bacterial exoglycosidases with remarkably improved kinetic properties for cleaving A and B antigens has reinvigorated the field. Enzymatic conversion of groups A, B and AB RBCs with these novel enzymes resulting in ECO RBCs typing as O can now be achieved with low enzyme protein consumption, short incubation times and at neutral pH. Presently, clinical trials evaluating safety and efficacy of ECO RBCs are ongoing. Here, we review the status of the ECO technology, its impact and potential for introduction into clinical component preparation laboratories.

Bacterial glycosidases for the production of universal red blood cells

Enzymatic removal of blood group ABO antigens to develop universal red blood cells (RBCs) was a pioneering vision originally proposed more than 25 years ago. Although the feasibility of this approach was demonstrated in clinical trials for group B RBCs, a major obstacle in translating this technology to clinical practice has been the lack of efficient glycosidase enzymes. Here we report two bacterial glycosidase gene families that provide enzymes capable of efficient removal of A and B antigens at neutral pH with low consumption of recombinant enzymes. The crystal structure of a member of the alpha-N-acetylgalactosaminidase family reveals an unusual catalytic mechanism involving NAD+. The enzymatic conversion processes we describe hold promise for achieving the goal of producing universal RBCs, which would improve the blood supply while enhancing the safety of clinical transfusions.

The molecular defect leading to Fabry disease: structure of human alpha-galactosidase

Fabry disease is an X-linked lysosomal storage disease afflicting 1 in 40,000 males with chronic pain, vascular degeneration, cardiac impairment, and other symptoms. Deficiency in the lysosomal enzyme alpha-galactosidase (alpha-GAL) causes an accumulation of its substrate, which ultimately leads to Fabry disease symptoms. Here, we present the structure of the human alpha-GAL glycoprotein determined by X-ray crystallography. The structure is a homodimer with each monomer containing a (beta/alpha)8 domain with the active site and an antiparallel beta domain. N-linked carbohydrate appears at six sites in the glycoprotein dimer, revealing the basis for lysosomal transport via the mannose-6-phosphate receptor. To understand how the enzyme cleaves galactose from glycoproteins and glycolipids, we also determined the structure of the complex of alpha-GAL with its catalytic product. The catalytic mechanism of the enzyme is revealed by the location of two aspartic acid residues (D170 and D231), which act as a nucleophile and an acid/base, respectively. As a point mutation in alpha-GAL can lead to Fabry disease, we have catalogued and plotted the locations of 245 missense and nonsense mutations in the three-dimensional structure. The structure of human alpha-GAL brings Fabry disease into the realm of molecular diseases, where insights into the structural basis of the disease phenotypes might help guide the clinical treatment of patients.

Universal red blood cells—enzymatic conversion of blood group A and B antigens

Accidental transfusion of ABO-incompatible red blood cells (RBCs) is a leading cause of fatal transfusion reactions. To prevent this and to create a universal blood supply, the idea of converting blood group A and B antigens to H using specific exo-glycosidases capable of removing the immunodominant sugar residues was pioneered by Goldstein and colleagues at the New York Blood Center in the early 1980s. Conversion of group B RBCs to O was initially carried out with alpha-galactosidase extracted from coffee beans. These enzyme-converted O (ECO) RBCs appeared to survive normally in all recipients independent of blood group. The clinical trials moved from small infusions to single RBC units and finally multiple and repeated transfusions. A successful phase II trial utilizing recombinant enzyme was reported by Kruskall and colleagues in 2000. Enzymatic conversion of group A RBCs has lagged behind due to lack of appropriate glycosidases and the more complex nature of A antigens. Identification of novel bacterial glycosidases with improved kinetic properties and specificities for the A and B antigens has greatly advanced the field. Conversion of group A RBCs can be achieved with improved glycosidases and the conversion conditions for both A and B antigens optimized to use more cost-efficient quantities of enzymes and gentler conditions including neutral pH and short incubation times at room temperature. Of the different strategies envisioned to create a universal blood supply, the ECO concept is the only one, for which human clinical trials have been performed. This paper discusses some biochemical and clinical aspects of this developing technology.

Cloning and functional expression of alkaline alpha-galactosidase from melon fruit: similarity to plant SIP proteins uncovers a novel family of plant glycosyl hydrolases

Raffinose and stachyose are ubiquitous galactosyl-sucrose oligosaccharides in the plant kingdom which play major roles, second only to sucrose, in photoassimilate translocation and seed carbohydrate storage. These sugars are initially metabolised by alpha-galactosidases (alpha-gal). We report the cloning and functional expression of the first genes, CmAGA1 and CmAGA2, encoding for plant alpha-gals with alkaline pH optima from melon fruit (Cucumis melo L.), a raffinose and stachyose translocating species. The alkaline alpha-gal genes show very high sequence homology with a family of undefined 'seed imbibition proteins' (SIPs) which are present in a wide range of plant families. In order to confirm the function of SIP proteins, a representative SIP gene, from tomato, was expressed and shown to have alkaline alpha-gal activity. Phylogenetic analysis based on amino acid sequences shows that the family of alkaline alpha-gals shares little homology with the known prokaryotic and eukaryotic alpha-gals of glycosyl hydrolase families 27 and 36, with the exception of two cross-family conserved sequences containing aspartates which probably function in the catalytic step. This previously uncharacterised, plant-specific alpha-gal family of glycosyl hydrolases, with optimal activity at neutral-alkaline pH likely functions in key processes of galactosyl-oligosaccharide metabolism, such as during seed germination and translocation of RFO photosynthate.

The 1.9 A structure of alpha-N-acetylgalactosaminidase: molecular basis of glycosidase deficiency diseases

In the lysosome, glycosidases degrade glycolipids, glycoproteins, and oligosaccharides. Mutations in glycosidases cause disorders characterized by the deposition of undegraded carbohydrates. Schindler and Fabry diseases are caused by the incomplete degradation of carbohydrates with terminal alpha-N-acetylgalactosamine and alpha-galactose, respectively. Here we present the X-ray structure of alpha-N-acetylgalactosaminidase (alpha-NAGAL), the glycosidase that removes alpha-N-acetylgalactosamine, and the structure with bound ligand. The active site residues of alpha-NAGAL are conserved in the closely related enzyme a-galactosidase A (alpha-GAL). The structure demonstrates the catalytic mechanisms of both enzymes and reveals the structural basis of mutations causing Schindler and Fabry diseases. As alpha-NAGAL and alpha-GAL produce type O "universal donor" blood from type A and type B blood, the alpha-NAGAL structure will aid in the engineering of improved enzymes for blood conversion.

The α-Gal epitope (Galα1-3Galβ1-4GlcNAc-R) in xenotransplantation

Many patients with failing organs (e.g., heart, liver or kidneys), do not receive the needed organ because of an insufficient number of organ donors. Pig xenografts have been considered as an alternative source of organs for transplantation. The major obstacle currently known to prevent pig to human xenotransplantation is the interaction between the human natural anti-Gal antibody and the α-gal epitope (Galα1-3Galβ1-4GlcNAc-R), abundantly expressed on pig cells. This short review describes the characteristics of anti-Gal and of the alpha-gal epitope, their role in inducing xenograft rejection and some experimental approaches for preventing this rejection.

A novel alkaline alpha-galactosidase from melon fruit with a substrate preference for raffinose

The cucurbits translocate the galactosyl-sucrose oligosaccharides raffinose and stachyose, therefore, alpha-galactosidase (alpha-D-galactoside galactohydrolase, EC 3.2.1.22) is expected to function as the initial enzyme of photoassimilate catabolism. However, the previously described alkaline alpha-galactosidase is specific for the tetrasaccharide stachyose, leaving raffinose catabolism in these tissues as an enigma. In this paper we report the partial purification and characterization of three alpha-galactosidases, including a novel alkaline alpha-galactosidase (form I) from melon (Cucumis melo) fruit tissue. The form I enzyme showed preferred activity with raffinose and significant activity with stachyose. Other unique characteristics of this enzyme, such as weak product inhibition by galactose (in contrast to the other alpha-galactosidases, which show stronger product inhibition), also impart physiological significance. Using raffinose and stachyose as substrates in the assays, the activities of the three alpha-galactosidases (alkaline form I, alkaline form II, and the acid form) were measured at different stages of fruit development. The form I enzyme activity increased during the early stages of ovary development and fruit set, in contrast to the other alpha-galactosidase enzymes, both of which declined in activity during this period. In the mature, sucrose-accumulating mesocarp, the alkaline form I enzyme was the major alpha-galactosidase present. We also observed hydrolysis of raffinose at alkaline conditions in enzyme extracts from other cucurbit sink tissues, as well as from young Coleus blumei leaves. Our results suggest different physiological roles for the alpha-galactosidase forms in the developing cucurbit fruit, and show that the newly discovered enzyme plays a physiologically significant role in photoassimilate partitioning in cucurbit sink tissue.

Porcine cartilage transplants in the cynomolgus monkey. III. Transplantation of alpha-galactosidase-treated porcine cartilage

BACKGROUND

Studies on transplantation of porcine meniscus and articular cartilage into monkeys are important for evaluating the possible use of such tissues in humans. In addition, such studies shed light on the chronic xenograft rejection process in primates. Transplantation of porcine cartilage into cynomolgus monkeys for 2 months results in a many-fold increase in anti-Gal activity and in a strong cellular inflammatory response of T lymphocytes and macrophages within the implants. The objective of this study was to determine whether elimination of Galalpha1-3Galbeta1-4GlcNAc-R (alpha-gal epitopes) from the xenograft may alter the immune response and the inflammatory reaction.

METHODS

Porcine meniscus and articular cartilage specimens were treated with recombinant alpha-galactosidase (100 U/ml), and the absence of alpha-gal epitopes was assessed by the binding of the monoclonal anti-Gal antibody M86. The treated cartilage specimens were transplanted into the suprapatellar pouch of cynomolgus monkeys. The immune response to cartilage was monitored in the serum and the inflammatory reaction was assessed in the xenografts, which were explanted after 2 months.

RESULTS

Incubation with alpha-galactosidase resulted in complete removal of alpha-gal epitopes from the cartilage. The increase in anti-Gal activity in the transplanted monkeys was marginal. However, most monkeys produced antibodies to antigens specific to porcine cartilage. The inflammatory response within the alpha-galactosidase-treated xenografts was much lower than in nontreated cartilage and the proportion of T lymphocytes within the cellular infiltrates was greatly reduced.

CONCLUSIONS

Treatment of cartilage xenografts with alpha-galactosidase successfully removes alpha-gal epitopes from porcine cartilage. Transplantation of the treated cartilage results in the production of only anti-porcine cartilage-specific antibodies and a reduced inflammatory response consisting primarily of macrophages infiltrating into the cartilage.

Production of recombinant proteins by methylotrophic yeasts

The methylotrophic yeasts Hansenula polymorpha, Pichia pastoris and Candida boidinii have been developed as production systems for recombinant proteins. The favourable and most advantageous characteristics of these species have resulted in an increasing number off biotechnological applications. As a consequence, these species--especially H. polymorpha and P. pastoris--are rapidly becoming the systems of choice for heterologous gene expression in yeast. Recent advances in the development of these yeasts as hosts for the production of heterologous proteins have provided a catalogue of new applications, methods and system components.

Trp-16 is essential for the activity of alpha-galactosidase and alpha-N-acetylgalactosaminidase

By expressing site-directed mutants in the methylotrophic yeast strain Pichia pastoris, the role of a tryptophan residue at position 16 in the activity of alpha-galactosidase and alpha-N-acetylgalactosaminidase, two closely related exoglycosidases, was studied. A substitution of Trp-16 with an arginine residue in alpha-N-acetylgalactosaminidase abolished the enzyme activity, which was confirmed by replacing a 600 bp fragment containing the mutation with the corresponding wild-type sequence. The same tryptophan residue was then substituted with an alanine in both enzymes by site-directed mutagenesis to reveal a possible relationship between their active sites. The purified alpha-N-acetylgalactosaminidase mutant demonstrated a specific activity of 2.8 x 10(-2) U/mg and a Vmax/K(m) of 4.3 x 10(-2), which were both more than a thousandfold lower than corresponding values for the wild-type enzyme. Furthermore, the mutant failed to bind to an affinity resin, suggesting the involvement of Trp-16 in substrate-binding. In addition, the purified alpha-galactosidase mutant resulted in more than a 10(4)-fold decrease in specific activity. Thus our data suggest that Trp-16 in both alpha-galactosidase and alpha-N-acetylgalactosaminidase is critical for enzymatic activity, which in turn supports the hypothesis that these two enzymes may share a catalytic mechanism involving similar residues in their active sites.