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

Prevention of Blood Incompatibility Related Hemagglutination: Blocking of Antigen A on Red Blood Cells Using In Silico Designed Recombinant Anti-A scFv

Critical blood shortages plague healthcare systems, particularly in lower-income and middle-income countries. This affects patients requiring regular transfusions and creates challenges during emergencies where universal blood is vital. To address these shortages and support blood banks during emergencies, this study reports a method for increasing the compatibility of blood group A red blood cells (RBCs) by blocking surface antigen-A using anti-A single chain fragment variable (scFv). To enhance stability, the scFv was first modified with the addition of interdomain disulfide bonds. The most effective location for this modification was found to be H44-L232 of mutant-1a scFv. ScFv was then produced from E.coli BL21(DE3) and purified using a three-step process. Purified scFvs were then used to block maximum number of antigens-A on RBCs, and it was found that only monomers were functional, while dimers formed through incorrect domain-swapping were non-functional. These antigen-blocked RBCs displayed no clumping in hemagglutination testing with incompatible blood plasma. The dissociation constant KD was found to be 0.724 μM. Antigen-blocked RBCs have the potential to be given to other blood groups during emergencies. This innovative approach could significantly increase the pool of usable blood, potentially saving countless lives.

Statistical optimization and sequential scale-up of α-galactosidase production by Actinoplanes utahensis B1 from shake flask to pilot scale

α-Galactosidase (α-GAL) is a class of hydrolase that releases galactose from galacto-oligosaccharides and synthetic substrates such as pNPG. In this study, the production of α-GAL by Actinoplanes utahensis B1 in submerged fermentation was enhanced by using statistical methods. The effects of temperature, pH, and inoculum percentage on enzyme secretion were optimized using BBD of RSM. The optimized process was scaled up from the shake flask to the laboratory scale (5 L) and to pilot scale (30 L) using KLa based scale-up strategy. By using BBD, a maximum yield of 62.5 U/mL was obtained at a temperature of 28 °C, a pH of 6.9, and an inoculum of 6.4%. Scale-up was performed successfully and achieved a yield of 74.4 U/mL and 76.8 U/mL in laboratory scale and pilot scale fermenters. The TOST was performed to validate the scale-up strategy and the results showed a confidence level of 95% for both scales indicating the perfect execution of scale-up procedure. Through the implementation of BBD and scale-up strategy, the overall enzyme yield has been significantly increased to 76%. This is the first article to explore the scale-up of α-GAL from the A. utahensis B1 strain and provide valuable insights for industrial applications.

Novel GH109 enzymes for bioconversion of group A red blood cells to the universal donor group O

Glycoside hydrolases (GHs) have been employed for industrial and biotechnological purposes and often play an important role in new applications. The red blood cell (RBC) antigen system depends on the composition of oligosaccharides on the surface of erythrocytes, thus defining the ABO blood type classification. Incorrect blood transfusions may lead to fatal consequences, making the availability of the correct blood group critical. In this regard, it has been demonstrated that some GHs may be helpful in the conversion of groups A and B blood types to produce group O universal donor blood. GHs belonging to the GH109 family are of particular interest for this application due to their ability to convert blood from group A to group O. This work describes the biochemical characterisation of three novel GH109 enzymes (NAg68, NAg69 and NAg71) and the exploration of their ability to produce enzymatically converted RBCs (ECO-RBC). The three enzymes showed superior specificity on pNP-α-N-acetylgalactosamine compared to previously reported GH109 enzymes. These novel enzymes were able to act on purified antigen-A trisaccharides and produce ECO-RBC from human donor blood. NAg71 converted type A RBC to group O with increased efficiency in the presence of dextran compared to a commercially available GH109, previously used for this application.

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.

Recent advances on the development of a universal blood type

Blood transfusion is the most common form of tissue transplant, and correct blood type matching is decisive for the success of this procedure. However, the availability of different blood types depends on each population, leading to a shortage of blood units from uncommon types. Then, it represents a problem for patients who need a blood transfusion because the supply for their blood type is scarce. Fortunately, researchers have been developing different techniques to engineer universal red blood cells (RBC) that could be transplanted to any human being independent of its blood type. This paper details the main features of blood transfusion and red blood cells maintenance and the two more recent procedures used to produce universal RBCs, the Enzymatically Converted Group O (ECO) and the antigen masking methods.

Schistosoma mansoni α-N-acetylgalactosaminidase (SmNAGAL) regulates coordinated parasite movement and egg production

α-galactosidase (α-GAL) and α-N-acetylgalactosaminidase (α-NAGAL) are two glycosyl hydrolases responsible for maintaining cellular homeostasis by regulating glycan substrates on proteins and lipids. Mutations in the human genes encoding either enzyme lead to neurological and neuromuscular impairments seen in both Fabry- and Schindler/Kanzaki- diseases. Here, we investigate whether the parasitic blood fluke Schistosoma mansoni, responsible for the neglected tropical disease schistosomiasis, also contains functionally important α-GAL and α-NAGAL proteins. As infection, parasite maturation and host interactions are all governed by carefully-regulated glycosylation processes, inhibiting S. mansoni's α-GAL and α-NAGAL activities could lead to the development of novel chemotherapeutics. Sequence and phylogenetic analyses of putative α-GAL/α-NAGAL protein types showed Smp_089290 to be the only S. mansoni protein to contain the functional amino acid residues necessary for α-GAL/α-NAGAL substrate cleavage. Both α-GAL and α-NAGAL enzymatic activities were higher in females compared to males (p<0.05; α-NAGAL > α-GAL), which was consistent with smp_089290's female biased expression. Spatial localisation of smp_089290 revealed accumulation in parenchymal cells, neuronal cells, and the vitellaria and mature vitellocytes of the adult schistosome. siRNA-mediated knockdown (>90%) of smp_089290 in adult worms significantly inhibited α-NAGAL activity when compared to control worms (siLuc treated males, p<0.01; siLuc treated females, p<0.05). No significant reductions in α-GAL activities were observed in the same extracts. Despite this, decreases in α-NAGAL activities correlated with a significant inhibition in adult worm motility as well as in egg production. Programmed CRISPR/Cas9 editing of smp_089290 in adult worms confirmed the egg reduction phenotype. Based on these results, Smp_089290 was determined to act predominantly as an α-NAGAL (hereafter termed SmNAGAL) in schistosome parasites where it participates in coordinating movement and oviposition processes. Further characterisation of SmNAGAL and other functionally important glycosyl hydrolases may lead to the development of a novel anthelmintic class of compounds.

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.

Toward universal donor blood: Enzymatic conversion of A and B to O type

Transfusion of blood, or more commonly red blood cells (RBCs), is integral to health care systems worldwide but requires careful matching of blood types to avoid serious adverse consequences. Of the four main blood types, A, B, AB, and O, only O can be given to any patient. This universal donor O-type blood is crucial for emergency situations where time or resources for typing are limited, so it is often in short supply. A and B blood differ from the O type in the presence of an additional sugar antigen (GalNAc and Gal, respectively) on the core H-antigen found on O-type RBCs. Thus, conversion of A, B, and AB RBCs to O-type RBCs should be achievable by removal of that sugar with an appropriate glycosidase. The first demonstration of a B-to-O conversion by Goldstein in 1982 required massive amounts of enzyme but enabled proof-of-principle transfusions without adverse effects in humans. New α-galactosidases and α-N-acetylgalactosaminidases were identified by screening bacterial libraries in 2007, allowing improved conversion of B and the first useful conversions of A-type RBCs, although under constrained conditions. In 2019, screening of a metagenomic library derived from the feces of an AB donor enabled discovery of a significantly more efficient two-enzyme system, involving a GalNAc deacetylase and a galactosaminidase, for A conversion. This promising system works well both in standard conditions and in whole blood. We discuss remaining challenges and opportunities for the use of such enzymes in blood conversion and organ transplantation.

Microbial production and biotechnological applications of α-galactosidase

α-Galactosidase, (E.C. 3.2.1.22) is an exoglycosidase that target galactooligosaccharides such as raffinose, melibiose, stachyose and branched polysaccharides like galactomannans and galacto-glucomannans by catalysing the hydrolysis of α-1,6 linked terminal galactose residues. The enzyme has been isolated and characterized from microbial, plant and animal sources. This ubiquitous enzyme possesses physiological significance and immense industrial potential. Optimization of the growth conditions and efficient purification strategies can lead to a significant increase in the enzyme production. To boost commercial productivity, cloning of novel α-galactosidase genes and their heterologous expression in suitable host has gained popularity. Enzyme immobilization leads to its greater reutilization, superior thermostability, pH tolerance and increased activity. The enzyme is well explored in food industry in the removal of raffinose family oligosaccharides (RFOs) in soymilk and sugar crystallization process. It also improves animal feed quality and biomass processing. Applications of the enzyme is in the area of biomedicine includes therapeutic advances in treatment of Fabry disease, blood group conversion and removal of α-gal type immunogenic epitopes in xenotransplantation. With considerable biotechnological applications, this enzyme has been vastly commercialized and holds greater future prospects.

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.

Thermus thermophilus as source of thermozymes for biotechnological applications: homologous expression and biochemical characterization of an α-galactosidase

Background

The genus Thermus, which has been considered for a long time as a fruitful source of biotechnological relevant enzymes, has emerged more recently as suitable host to overproduce thermozymes. Among these, α-galactosidases are widely used in several industrial bioprocesses that require high working temperatures and for which thermostable variants offer considerable advantages over their thermolabile counterparts.

Results

Thermus thermophilus HB27 strain was used for the homologous expression of the TTP0072 gene encoding for an α-galactosidase (TtGalA). Interestingly, a soluble and active histidine-tagged enzyme was produced in larger amounts (5 mg/L) in this thermophilic host than in Escherichia coli (0.5 mg/L). The purified recombinant enzyme showed an optimal activity at 90 °C and retained more than 40% of activity over a broad range of pH (from 5 to 8).

Conclusions

TtGalA is among the most thermoactive and thermostable α-galactosidases discovered so far, thus pointing to T. thermophilus as cell factory for the recombinant production of biocatalysts active at temperature values over 90 °C.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0638-4) contains supplementary material, which is available to authorized users.

Optimization of cold-adapted alpha-galactosidase expression in Escherichia coli

α-Galactosidase (α-PsGal) of the cold-adapted marine bacterium Pseudoalteromonas sp. KMM 701 was cloned into the pET-40b(+) vector to study its properties and to develop an effective method for modifying human B-erythrocytes into O-blood group. The use of heat-shock as a pre-induction treatment, IPTG concentration of 0.2 mM and post-induction cultivation at 18 °C for 20 h in the developed MX-medium allowed increasing the recombinant Escherichia coli Rosetta (DE3)/40Gal strain productivity up to 30 times and the total soluble α-PsGal yield up to 40 times.

Effect of Induced Pluripotent Stem Cell Technology in Blood Banking

Population aging has imposed cost-effective alternatives to blood donations. Artificial blood is still at the preliminary stages of development, and the need for viable cells seems unsurmountable. Because large numbers of viable cells must be promptly available for clinical use, stem cell technologies, expansion, and banking represent ideal tools to ensure a regular supply. Provided key donors can be identified, induced pluripotent stem cell (iPSC) technology could pave the way to a new era in transfusion medicine, just as it is already doing in many other fields of medicine. The present review summarizes the current state of research on iPSC technology in the field of blood banking, highlighting hurdles, and promises.

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.

Toward Efficient Enzymes for the Generation of Universal Blood through Structure-Guided Directed Evolution

Blood transfusions are critically important in many medical procedures, but the presence of antigens on red blood cells (RBCs, erythrocytes) means that careful blood-typing must be carried out prior to transfusion to avoid adverse and sometimes fatal reactions following transfusion. Enzymatic removal of the terminal N-acetylgalactosamine or galactose of A- or B-antigens, respectively, yields universal O-type blood, but is inefficient. Starting with the family 98 glycoside hydrolase from Streptococcus pneumoniae SP3-BS71 (Sp3GH98), which cleaves the entire terminal trisaccharide antigenic determinants of both A- and B-antigens from some of the linkages on RBC surface glycans, through several rounds of evolution, we developed variants with vastly improved activity toward some of the linkages that are resistant to cleavage by the wild-type enzyme. The resulting enzyme effects more complete removal of blood group antigens from cell surfaces, demonstrating the potential for engineering enzymes to generate antigen-null blood from donors of various types.

Stereochemical course of hydrolytic reaction catalyzed by alpha-galactosidase from cold adaptable marine bacterium of genus Pseudoalteromonas

The recombinant α-galactosidase of the marine bacterium (α-PsGal) was synthesized with the use of the plasmid 40Gal, consisting of plasmid pET-40b (+) (Novagen) and the gene corresponding to the open reading frame of the mature α-galactosidase of marine bacterium Pseudoalteromonas sp. KMM 701, transformed into the Escherichia coli Rosetta(DE3) cells. In order to understand the mechanism of action, the stereochemistry of hydrolysis of 4-nitrophenyl α-D-galactopyranoside (4-NPGP) by α-PsGal was measured by ¹H NMR spectroscopy. The kinetics of formation of α- and β-anomer of galactose showed that α-anomer initially formed and accumulated, and then an appreciable amount of β-anomer appeared as a result of mutarotation. The data clearly show that the enzymatic hydrolysis of 4-NPGP proceeds with the retention of anomeric configuration, probably, due to a double displacement mechanism of reaction.

Enhancement of biological reactions on cell surfaces via macromolecular crowding

The reaction of macromolecules such as enzymes and antibodies with cell surfaces is often an inefficient process, requiring large amounts of expensive reagent. Here we report a general method based on macromolecular crowding with a range of neutral polymers to enhance such reactions, using red blood cells (RBCs) as a model system. Rates of conversion of type A and B red blood cells to universal O type by removal of antigenic carbohydrates with selective glycosidases are increased up to 400-fold in the presence of crowders. Similar enhancements are seen for antibody binding. We further explore the factors underlying these enhancements using confocal microscopy and fluorescent recovery after bleaching (FRAP) techniques with various fluorescent protein fusion partners. Increased cell-surface concentration due to volume exclusion, along with two-dimensionally confined diffusion of enzymes close to the cell surface, appear to be the major contributing factors.

A mechanistic study on the α-N-acetylgalactosaminidase from E. meningosepticum: a family 109 glycoside hydrolase

Studies on the mechanism of action used by a GH109 enzyme.

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.

Bifidobacterial α-galactosidase with unique carbohydrate-binding module specifically acts on blood group B antigen

Bifidobacterium bifidum is one of the most frequently found bifidobacteria in the intestines of newborn infants. We previously reported that B. bifidum possesses unique metabolic pathways for O-linked glycans on gastrointestinal mucin (Yoshida E, Sakurama H, Kiyohara M, Nakajima M, Kitaoka M, Ashida H, Hirose J, Katayama T, Yamamoto K, Kumagai H. 2012. Bifidobacterium longum subsp. infantis uses two different β-galactosidases for selectively degrading type-1 and type-2 human milk oligosaccharides. Glycobiology. 22:361-368). The nonreducing termini of O-linked glycans on mucin are frequently covered with histo-blood group antigens. Here, we identified a gene agabb from B. bifidum JCM 1254, which encodes glycoside hydrolase (GH) family 110 α-galactosidase. AgaBb is a 1289-amino acid polypeptide containing an N-terminal signal sequence, a GH110 domain, a carbohydrate-binding module (CBM) 51 domain, a bacterial Ig-like (Big) 2 domain and a C-terminal transmembrane region, in this order. The recombinant enzyme expressed in Escherichia coli hydrolyzed α1,3-linked Gal in branched blood group B antigen [Galα1-3(Fucα1-2)Galβ1-R], but not in a linear xenotransplantation antigen (Galα1-3Galβ1-R). The enzyme also acted on group B human salivary mucin and erythrocytes. We also revealed that CBM51 specifically bound blood group B antigen using both isothermal titration calorimetry and a solid-phase binding assay, and it enhanced the affinity of the enzyme toward substrates with multivalent B antigens. We suggest that this enzyme plays an important role in degrading B antigens to acquire nutrients from mucin oligosaccharides in the gastrointestinal tracts.

Interaction of Naja naja atra cardiotoxin 3 with H-trisaccharide modulates its hemolytic activity and membrane-damaging activity

To address whether saccharide moieties of blood groups A, B and O antigens modulate hemolytic activity of Naja naja atra cardiotoxins (CTXs), the present study was carried out. Unlike other CTX isotoxins, hemolytic activity of CTX3 toward blood group O cholesterol-depleted red blood cells (RBCs) was notably lower than that of blood groups A and B cholesterol-depleted RBCs. Conversion of blood group B RBCs into blood group O RBCs by alpha-galactosidase treatment attenuated the susceptibility for hemolytic activity of CTX3, suggesting that H-antigen affected hemolytic potency of CTX3. Pre-incubation with H-trisaccharide reduced hemolytic activity and membrane-damaging activity of CTX3. Moreover, CTX3 showed a higher binding capability with H-trisaccharide than other CTXs did. CD spectra showed that the binding with H-trisaccharide induced changes in gross conformation of CTX3. Self-quenching studies revealed that oligomerization of CTX3 was affected in the presence of H-trisaccharide. Taken together, our data suggest that the binding of CTX3 with H-antigen alters its membrane-bound mode, thus reducing its hemolytic activity toward blood group O cholesterol-depleted RBCs.

Molecular characterization and therapeutic potential of a marine bacterium Pseudoalteromonas sp. KMM 701 alpha-galactosidase

An alpha-galactosidase capable of converting B red blood cells into the universal blood type cells at the neutral pH was produced by a novel obligate marine bacterium strain KMM 701 (VKM B-2135 D). The organism is heterotrophic, aerobic, and halophilic and requires Na+ ions and temperature up to 34 degrees C for its growth. The strain has a unique combination of polysaccharide-degrading enzymes. Its single intracellular alpha-galactosidase exceeded other glycoside hydrolases in the level of expression up to 20-fold. The alpha-galactosidase was purified to determine the N-terminal amino acid sequences and new activities. It was found to inhibit Corynebacterium diphtheria adhesion to host buccal epithelium cell surfaces with high effectiveness. The nucleotide sequence of the homodimeric alpha-galactosidase indicates that its subunit is composed of 710 amino acid residues with a calculated Mr of 80,055. This alpha-galactosidase shares structural property with 36 family glycoside hydrolases. The properties of the enzyme are likely to be highly beneficial for medicinal purposes.

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.

Red blood cell transfusion in clinical practice

Every year, about 75 million units of blood are collected worldwide. Red blood cell (RBC) transfusion is one of the few treatments that adequately restore tissue oxygenation when oxygen demand exceeds supply. Although the respiratory function of blood has been studied intensively, the trigger for RBC transfusion remains controversial, and doctors rely primarily on clinical experience. Laboratory assays that indicate failing tissue oxygenation would be ideal to guide the need for transfusion, but none has proved easy, reproducible, and sensitive to regional tissue hypoxia. The clinical importance of the RBCs storage lesion (ie, the time-dependent metabolic, biochemical, and molecular changes that stored blood cells undergo) is poorly understood. RBCs can be filtered, washed, frozen, or irradiated for specific indications. Donor screening and testing have dramatically reduced infectious risks in the developed world, but infection remains a major hazard in developing countries, where 13 million units of blood are not tested for HIV or hepatitis viruses. Pathogen inactivation techniques are in clinical trials for RBCs, but none is available for use. Despite serious immunological and non-immunological complications, RBC transfusion holds a therapeutic index that exceeds that of many common medications.

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.

Marine glycosyl hydrolases in the hydrolysis and synthesis of oligosaccharides

The marine ecosystem can be considered a rather unexplored source of biological material (e.g. natural substances with therapeutic activity) and can also be a surprising source of enzymes carrying new and interesting catalytic activities to be applied in biocatalysis. The use of glycosyl hydrolases from marine environments dates back to the end of the 1960s and was mainly focused on the development of sensitive and reliable hydrolytic methods for the analysis of sugar chains. As a result not all the benefits of a particular enzymatic activity have been investigated, especially regarding the transglycosylation potential of these enzymes for the synthesis of glycosidic bonds. In this review, the potential of marine sources will be demonstrated reporting on the few examples found in literature for the synthesis and hydrolysis of biologically relevant oligosaccharides catalyzed by glycosyl hydrolases of marine origin. Particular emphasis is given to the synthesis of glycosidic bonds, which is easy by the use of glycosyl hydrolases. Further aspects considered in this review are applications of these biocatalysts for vegetal waste treatment in recovering useful materials, for structural identification and for preparation of target materials from new purified polysaccharides, for the synthesis or modification of food-related compounds and for glycobiology related studies.

Induction and characterization of an unusual alpha-D-galactosidase from Talaromyces flavus

An extracellular alpha-d-galactosidase from Talaromyces flavus CCF 2686 with extremely broad and unusual acceptor specificity is produced exclusively in the presence of the specific inducer--6-deoxy-D-glucose (quinovose). The procedure for the preparation of this very expensive substance has been modified and optimized. Surprisingly, any of other common alpha-D-galactosidase inducers or substrates, e.g., D-galactose, melibiose and raffinose, did not stimulate its production. The crude alpha-D-galactosidase preparation was purified by anion-exchange chromatography and three isoenzymes with different substrate specificities were identified. The main isoenzyme (alphaGal1) was further purified by cation-exchange chromatography and fully characterized. When compared with other alpha-galactosidases and also with other isoenzymes produced by T. flavus, it showed a markedly different regioselectivity and also negligible hydrolytic activity towards melibiose. Moreover, it was active on polymeric substrates (locust bean gum, guar gum) and significantly inhibited by alpha-D-galactopyranosyl azide, D-galactose, D-xylose, melibiose, methyl alpha- and beta-D-galactopyranoside and lactose.

Surface decoration of red blood cells with maleimidophenyl-polyethylene glycol facilitated by thiolation with iminothiolane: an approach to mask A, B, and D antigens to generate universal red blood cells

BACKGROUND

The surface decoration of red blood cells (RBCs) by polyethylene glycol (PEG) chains has been an approach developed to camouflage the blood group antigens from their antibodies. A PEGylation protocol, however, that can mask the antigens appropriately to inhibit the agglutination of RBCs with the respective antibodies is not available so far.

STUDY DESIGN AND METHODS

A new approach for PEGylation of RBC membrane proteins has been designed with thiolation-mediated maleimide chemistry. The accessibility of the surface lysine residues of membrane proteins to bulky PEG reagents was increased by linking an extension arm carrying a thiol group.

RESULTS

RBCs have been PEGylated by thiolation-mediated chemistry with maleimidophenyl-PEG (Mal-Phe-PEG) reagents of different chain lengths. Mal-Phe-PEG-5000 chains alone masked the most important antigens of the Rh system (C, c, E, e, and D) from their antibodies. The masking of the A and B antigens needed a combination of Mal-Phe-PEG-5000 and Mal-Phe-PEG-20000 chains to inhibit the agglutination of RBCs completely with anti-A or anti-B.

CONCLUSIONS

Thiolation-mediated PEGylation of RBCs with Mal-Phe-PEG-5000 and Mal-Phe-PEG-20000 converts Group A Rh(D)+ and B Rh(D)+ RBCs into RBCs with serologic behavior comparable to Group O Rh(D)- RBCs that are considered as universal RBCs for transfusion.