Neutral hydrolases of rat brain. Preliminary characterization and developmental changes of neutral beta-N-acetylhexosamindases

Bioinformatic, Enzymatic, and Structural Characterization of Trichuris suis Hexosaminidase HEX-2

Hexosaminidases are key enzymes in glycoconjugate metabolism and occur in all kingdoms of life. Here, we have investigated the phylogeny of the GH20 glycosyl hydrolase family in nematodes and identified a β-hexosaminidase subclade present only in the Dorylaimia. We have expressed one of these, HEX-2 from Trichuris suis, a porcine parasite, and shown that it prefers an aryl β-N-acetylgalactosaminide in vitro. HEX-2 has an almost neutral pH optimum and is best inhibited by GalNAc-isofagomine. Toward N-glycan substrates, it displays a preference for the removal of GalNAc residues from LacdiNAc motifs as well as the GlcNAc attached to the α1,3-linked core mannose. Therefore, it has a broader specificity than insect fused lobe (FDL) hexosaminidases but one narrower than distant homologues from plants. Its X-ray crystal structure, the first of any subfamily 1 GH20 hexosaminidase to be determined, is closest to Streptococcus pneumoniae GH20C and the active site is predicted to be compatible with accommodating both GalNAc and GlcNAc. The new structure extends our knowledge about this large enzyme family, particularly as T. suis HEX-2 also possesses the key glutamate residue found in human hexosaminidases of either GH20 subfamily, including HEXD whose biological function remains elusive.

Progress and mechanism of breaking glycoconjugates by glycosidases in skin for promoting unhairing and fiber opening-up in leather manufacture. A review

Abstract

The glycoconjugates, herein glyco-proteins, existing in animal skins are closely related to the effectiveness of unhairing and fiber opening-up. Glycosidases have been used in leather making processes to reduce pollutants and improve leather quality. But the selection of glycosidases is still blind because the related mechanisms are not well understood yet. Hence, the animal skin structures and glycoconjugates components, the advances in the methods and mechanisms of removing glycoconjugates related to unhairing and fiber opening-up in leather manufacture, the kinds, compositions, structures and functions of typical glycoconjugates in skin are summarized. Then the approaches to destroy them, possible glycosidases suitable for leather making and their acting sites are analyzed based on the recognition of glycoconjugates in skin and the specificities of glycosidases toward substrates. It is expected to provide useful information for the optimization of glycosidases and the development of new enzymes and the cleaner technologies of unhairing and opening up fiber bundles assisted by glycosidases.

Graphical abstract

Mammalian cells contain a second nucleocytoplasmic hexosaminidase

Some thirty years ago, work on mammalian tissues suggested the presence of two cytosolic hexosaminidases in mammalian cells; one of these has been more recently characterized in a recombinant form and has an important role in cellular function due to its ability to cleave beta-N-acetylglucosamine residues from a variety of nuclear and cytoplasmic proteins. However, the molecular nature of the second cytosolic hexosaminidase, named hexosaminidase D, has remained obscure. In the present study, we molecularly characterize for the first time the human and murine recombinant forms of enzymes, encoded by HEXDC genes, which appear to correspond to hexosaminidase D in terms of substrate specificity, pH dependency and temperature stability. Furthermore, a Myc-tagged form of this novel hexosaminidase displays a nucleocytoplasmic localization. Transcripts of the corresponding gene are expressed in a number of murine tissues. On the basis of its sequence, this enzyme represents, along with the lysosomal hexosaminidase subunits encoded by the HEXA and HEXB genes, the third class 20 glycosidase to be identified from mammalian sources.

Isoenzyme pattern and partial characterization of hexosaminidases in the membrane and cytosol of human erythrocytes

OBJECTIVES

Hexosaminidase activity is present in lysosomes, plasma membrane and cytosol of many human cells. Plasma membrane and cytosolic hexosaminidase is not well characterized, particularly as regards their isoenzyme forms and their relationship with the lysosomal ones.

DESIGN AND METHODS

Erythrocyte hexosaminidase isoforms were chromatographically separated, characterized and compared to those in the plasma of healthy individuals and in the erythrocytes of a Tay-Sachs patient.

RESULTS

Hexosaminidase isoenzymes were found in plasma membrane and cytosol and were composed of the same alpha- and beta-subunits as the lysosomal and plasma hexosaminidase A and B isoenzymes, though with some structural and kinetic differences. In addition, the cytosol contained a hexosaminidase that is a specific N-acetyl-beta-D-glucosaminidase, the one involved in the removal of N-acetylglucosamine residues O-linked to proteins, named O-GlcNAcase.

CONCLUSIONS

This work provides an additional step in the characterization of hexosaminidases helping better understand their role in non-lysosomal compartments and their involvement in physiological or pathological situations.

Dynamic O-glycosylation of nuclear and cytosolic proteins: cloning and characterization of a neutral, cytosolic beta-N-acetylglucosaminidase from human brain

Dynamic modification of cytoplasmic and nuclear proteins by O-linked N-acetylglucosamine (O-GlcNAc) on Ser/Thr residues is ubiquitous in higher eukaryotes and is analogous to protein phosphorylation. The enzyme for the addition of this modification, O-GlcNAc transferase, has been cloned from several species. Here, we have cloned a human brain O-GlcNAcase that cleaves O-GlcNAc off proteins. The cloned cDNA encodes a polypeptide of 916 amino acids with a predicted molecular mass of 103 kDa and a pI value of 4.63, but the protein migrates as a 130-kDa band on SDS-polyacrylamide gel electrophoresis. The cloned O-GlcNAcase has a pH optimum of 5.5-7.0 and is inhibited by GlcNAc but not by GalNAc. p-Nitrophenyl (pNP)-beta-GlcNAc, but not pNP-beta-GalNAc or pNP-alpha-GlcNAc, is a substrate. The cloned enzyme cleaves GlcNAc, but not GalNAc, from glycopeptides. Cell fractionation suggests that the overexpressed protein is mostly localized in the cytoplasm. It therefore has all the expected characteristics of O-GlcNAcase and is distinct from lysosomal hexosaminidases. Northern blots show that the transcript is expressed in every human tissue examined but is the highest in the brain, placenta, and pancreas. An understanding of O-GlcNAc dynamics and O-GlcNAcase may be key to elucidating the relationships between O-phosphate and O-GlcNAc and to the understanding of the molecular mechanisms of diseases such as diabetes, cancer, and neurodegeneration.

Purification and properties of neutral beta-N-acetylglucosaminidase from carp blood

A neutral beta-N-acetylglucosaminidase has been purified to homogeneity from carp blood by a seven-step procedure. It was localized in the cytosol of red blood cells. The purified enzyme was specific to beta-N-acetylglucosaminide and inactive to beta-N-acetylgalactosaminide. It was competitively inhibited by free N-acetylglucosamine, but not by free N-acetylgalactosamine. The optimum pH of the enzyme was 6.5, with a stable pH range of 7.0 to 11.0. The enzyme showed greater heat-lability and anodal electrophoretic mobility than acidic beta-N-acetylglucosaminidases. The Mr value, estimated by sucrose density gradient centrifugation, was 122,000, and the enzyme dissociated into two nonidentical subunits with Mr values of 66,000 and 53,000, based on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. With respect to the major characteristics, the neutral enzyme in carp blood was supposed to be a counterpart of hexosaminidase C in human and other mammalian tissues.

Purification and properties of beta-N-acetylhexosaminidase A from pig brain

1. Adult pig brain beta-N-acetylhexosaminidase was separated into four different forms by ion exchange chromatography on diethylaminoethyl-cellulose. 2. Form A was purified 1300-1500 fold by an unusual procedure, the technique of ampholyte displacement, followed by chromatography on concanavalin A Sepharose. 3. The enzyme catalyses the hydrolysis of both beta-N-acetylglucosaminides and beta-N-acetylgalactosaminides. 4. The kinetic studies support the evidence of the association of both activities to a single protein, and at the same active site. 5. A natural substrate, N,N'-diacetylchitobiose, is also hydrolyzed, but not ovalbumin. 6. This enzyme may be considered as an exoglycosidase.

Separation and characterization of four forms of beta-N-acetylhexosaminidase from chicken brain

Chicken brain beta-N-acetylhexosaminidases from embryos (16 and 21 days old), newborns (1 and 4 days old), and adults (3 1/2 months and 2 years old) were separated into four different forms by ion exchange chromatography on diethylaminoethyl-cellulose. Three of these forms were "acid" hexosaminidases (I, IIA, and IIB), and the fourth was a "neutral" form. Throughout development of the chicken, forms IIA and III maintained the same activity ratio, whereas that for form I decreased and that for form IIB showed an increase.

Kinetic studies of four enzyme forms of beta-N-acetylhexosaminidase from embryonic chicken brain

The separation of four different hexosaminidase forms from embryonic chicken brain (16-day-old) has been performed by ion-exchange chromatography. Two different DEAE-cellulose columns have been used: a first one at pH 7.2 and a second one at pH 6.0. Km and Vmax values were estimated from the Lineweaver-Burk or Dixon plots and ki from the Dixon plots, using N-acetyl-D-glucosamine or N-acetyl-D-galactosamine as inhibitors. In both cases we found a kind of competitive inhibition in which Lineweaver-Burk and Dixon plots curve downwards.

Influence of chemical modification on enzyme inactivation kinetics and stability

Enzymes are placed in different categories depending on the effect of chemical modification on their inactivation kinetics and residual activity. This is done using a series-type mechanism involving degraded but stable enzyme states. The major distinction in the three basic categories is the effect of modification on residual activity. Each category is further sub-divided depending on the effect of modification on the values of the deactivation rate constants. The classification provides for a framework for comparison of a wide variety of enzyme deactivation data. Structure-function relations are provided wherever possible.

beta-N-acetyl-D-glucosaminidase activity levels in atrophic gastrocnemius muscle of Rana esculenta

1. The atrophic status induced by long-term sciatectomy or tenotomy is different, since only in the first case have we found an irreversible muscular degeneration. 2. Up to 20 days after denervation or tenotomy the beta-N-acetylglucosaminidase showed increased specific activity. 3. The time-course of the beta-NAG increase is closely correlated with the loss of contractile capacity. 4. beta-NAG increases to 170% and does not fall in 20 days after cutting the nerve; but increases to 150% on day 4 and falls to 130% on day 20 after tenotomy.