Effects of N-glycosylation on the activity and localization of GlcNAc-6-sulfotransferase 1

Hydrophilic Interaction Liquid Chromatography (HILIC) Enrichment of Glycopeptides Using PolyHYDROXYETHYL A

Glycosylation of proteins is an important post-translational modification that plays a role in a wide range of biological processes, including immune response, intercellular signaling, inflammation, and host-pathogen interaction. Abnormal protein glycosylation has been correlated with various diseases. However, the study of protein glycosylation remains challenging due to its low abundance, microheterogeneity of glycosylation sites, and low ionization efficiency. During the past decade, several methods for enrichment and for isolation of glycopeptides from biological samples have been developed and successfully employed in glycoproteomics research. In this chapter, we discuss the sample preparation protocol and the strategies for effectively isolating and enriching glycopeptides from biological samples, using PolyHYDROXYETHYL A as a hydrophilic interaction liquid chromatography (HILIC) enrichment technique.

CHST2-mediated sulfation of MECA79 antigens is critical for breast cancer cell migration and metastasis

Snail is a denoted transcriptional repressor that plays key roles in epithelial-mesenchymal transition (EMT) and metastasis. Lately, a plethora of genes can be induced by stable expression of Snail in multiple cell lines. However, the biological roles of these upregulated genes are largely elusive. Here, we report identification of a gene encoding the key GlcNAc sulfation enzyme CHST2 is induced by Snail in multiple breast cancer cells. Biologically, CHST2 depletion results in inhibition of breast cancer cell migration and metastasis, while overexpression of CHST2 promotes cell migration and lung metastasis in nude mice. In addition, the expression level of MECA79 antigen is elevated and blocking the cell surface MECA79 antigen with specific antibodies can override cell migration mediated by CHST2 upregulation. Moreover, the sulfation inhibitor sodium chlorate effectively inhibits the cell migration induced by CHST2. Collectively, these data provide novel insights into the biology of Snail/CHST2/MECA79 axis in breast cancer progression and metastasis as well as potential therapeutic strategy for the diagnosis and treatment of breast cancer metastasis.

Redesigning N-glycosylation sites in a GH3 β-xylosidase improves the enzymatic efficiency

BACKGROUND

β-Xylosidases are glycoside hydrolases (GHs) that cleave xylooligosaccharides and/or xylobiose into shorter oligosaccharides and xylose. Aspergillus nidulans is an established genetic model and good source of carbohydrate-active enzymes (CAZymes). Most fungal enzymes are N-glycosylated, which influences their secretion, stability, activity, signalization, and protease protection. A greater understanding of the N-glycosylation process would contribute to better address the current bottlenecks in obtaining high secretion yields of fungal proteins for industrial applications.

RESULTS

In this study, BxlB-a highly secreted GH3 β-xylosidase from A. nidulans, presenting high activity and several N-glycosylation sites-was selected for N-glycosylation engineering. Several glycomutants were designed to investigate the influence of N-glycans on BxlB secretion and function. The non-glycosylated mutant (BxlB^non-glyc) showed similar levels of enzyme secretion and activity compared to the wild-type (BxlB^wt), while a partially glycosylated mutant (BxlB^N1;5;7) exhibited increased activity. Additionally, there was no enzyme secretion in the mutant in which the N-glycosylation context was changed by the introduction of four new N-glycosylation sites (BxlB^CC), despite the high transcript levels. BxlB^wt, BxlB^non-glyc, and BxlB^N1;5;7 formed similar secondary structures, though the mutants had lower melting temperatures compared to the wild type. Six additional glycomutants were designed based on BxlB^N1;5;7, to better understand its increased activity. Among them, the two glycomutants which maintained only two N-glycosylation sites each (BxlB^N1;5 and BxlB^N5;7) showed improved catalytic efficiency, whereas the other four mutants' catalytic efficiencies were reduced. The N-glycosylation site N5 is important for improved BxlB catalytic efficiency, but needs to be complemented by N1 and/or N7. Molecular dynamics simulations of BxlB^non-glyc and BxlB^N1;5 reveals that the mobility pattern of structural elements in the vicinity of the catalytic pocket changes upon N1 and N5 N-glycosylation sites, enhancing substrate binding properties which may underlie the observed differences in catalytic efficiency between BxlB^non-glyc and BxlB^N1;5.

CONCLUSIONS

This study demonstrates the influence of N-glycosylation on A. nidulans BxlB production and function, reinforcing that protein glycoengineering is a promising tool for enhancing thermal stability, secretion, and enzymatic activity. Our report may also support biotechnological applications for N-glycosylation modification of other CAZymes.

Role of N-linked glycosylation in the secretion and enzymatic properties of Rhizopus chinensis lipase expressed in Pichia pastoris

Background

The methylotrophic yeast, Pichia pastoris, is widely used as a useful experimental tool in protein engineering and production. It is common for proteins expressed in P. pastoris to exhibit N-glycosylation. In recent years, glycosylation studies in P. pastoris have attracted increasing attention from scholars. Rhizopus chinensis lipase (RCL) is one of the most important industrial lipases, and it has four potential N-linked glycosylation sites. The aim of the present study was to determine whether RCL undergoes asparagine-linked (N-linked) glycosylation and to examine the role of this modification in RCL expression and function.

Results

In this study, we demonstrated that RCL expressed in Pichia pastoris was N-glycosylated at the sites N-14, N-48 and N-60. The majority of the sites N-14 and N-60 were glycosylated, but the glycosylation degree of the site N-48 was only a very small portion. The glycan on N-60 played a key role in the expression and secretion of RCL. RT-PCR results showed that the mRNA level of proRCLCN60Q remained unchanged even though the protein secretion was hampered. Although the N-glycan on N-14 had no effect on the secretion of RCL, this glycan was beneficial for the lipase catalytic activity. On the other hand, the little amount of N-glycan on N-48 had no effect both on the secretion and activity of RCL in P. pastoris. Moreover, the thermostability analysis of RCL revealed that the lipase with more N-glycan was more thermostable.

Conclusions

RCL was N-glycosylated when expressed in P. pastoris. The N-glycans of RCL on the different sites had different functions for the secretion and enzymatic properties of the lipase. Our report may also provide theoretical support for the improvement of enzyme expression and stability based on the N-linked glycosylation modification to meet the future needs of the biotechnological industry.

Cellular ion homeostasis: emerging roles of intracellular NHX Na+/H+ antiporters in plant growth and development

Recent evidence highlights novel roles for intracellular Na(+)/H(+) antiporters (NHXs) in plants. The availability of knockouts and overexpressors of specific NHX isoforms has provided compelling genetic evidence to support earlier physiological and biochemical data which suggested the involvement of NHX antiporters in ion and pH regulation. Most plants sequenced to date contain multiple NHX members and, based on their sequence identity and localization, can be grouped into three distinct functional classes: plasma membrane, vacuolar, and endosomal associated. Orthologues of each functional class are represented in all sequenced plant genomes, suggesting conserved and fundamental roles across taxa. In this review we seek to highlight recent findings which demonstrate that intracellular NHX antiporters (i.e. vacuolar and endosomal isoforms) play roles in growth and development, including cell expansion, cell volume regulation, ion homeostasis, osmotic adjustment, pH regulation, vesicular trafficking, protein processing, cellular stress responses, as well as flowering. A significant new discovery demonstrated that in addition to the better known vacuolar NHX isoforms, plants also contain endosomal NHX isoforms that regulate protein processing and trafficking of cellular cargo. We draw parallels from close orthologues in yeast and mammals and discuss distinctive NHX functions in plants.

Expression of long-form N-acetylglucosamine-6-O-sulfotransferase 1 in human high endothelial venules

Two members of the N-acetylglucosamine-6-O-sulfotransferase (GlcNAc6ST) family, GlcNAc6ST-1 and GlcNAc6ST-2, function in the biosynthesis of 6-sulfo sialyl Lewis X-capped glycoproteins expressed on high endothelial venules (HEVs) in secondary lymphoid organs. Thus, both enzymes play a critical role in L-selectin-expressing lymphocyte homing. Human GlcNAc6ST-1 is encoded by a 1593-bp open reading frame exhibiting two 5' in-frame methionine codons spaced 141 bp apart. Both resemble the consensus sequence for translation initiation. Thus, it has been hypothesized that both long and short forms of GlcNAc6ST-1 may be present, although endogenous expression of either form has not been confirmed in humans. Here, the authors developed an antibody recognizing amino acid residues between the first two human GlcNAc6ST-1 methionines. This antibody specifically recognizes the long form of the enzyme, a finding validated by Western blot analysis and immunofluorescence cytochemistry of HeLa cells misexpressing long and/or short forms of human GlcNAc6ST-1. Using this antibody, the authors carried out immunofluorescence histochemistry of human lymph node tissue sections and found endogenous expression of the long form of the enzyme in human tissue, predominantly in the trans-Golgi network of endothelial cells that form HEVs.

Highly efficient chemoenzymatic synthesis of beta1-4-linked galactosides with promiscuous bacterial beta1-4-galactosyltransferases

Two bacterial beta1-4-galactosyltransferases, NmLgtB and Hp1-4GalT, exhibit promiscuous and complementary acceptor substrate specificity. They have been used in an efficient one-pot multienzyme system to synthesize LacNAc, lactose, and their derivatives including those containing negatively charged 6-O-sulfated GlcNAc and C2-substituted GlcNAc or Glc, from monosaccharide derivatives and inexpensive Glc-1-P.