Cooperative role of calnexin and TigA in Aspergillus oryzae glycoprotein folding

Preparation of natural high-mannose-type oligosaccharides (Glc1Man9GlcNAc2) with the asparagine-glycine-threonine as consensus sequence from chicken egg yolk

High-mannose-type glycan structure of N-glycoproteins plays important roles in the proper folding of proteins in sorting glycoprotein secretion and degradation of misfolded proteins in the endoplasmic reticulum (ER). The Glc1Man9GlcNAc2 (G1M9)-type N-glycan is one of the most important signaling molecules in the ER. However, current chemical synthesis strategies are laborious, warranting more practical approaches for G1M9-glycopeptide development. Wang et al. reported the procedure to give G1M9-Asn-Fmoc through chemical modifications and purifications from 40 chicken eggs, but only 3.3 mg of G1M9-glycopeptide was obtained. Therefore, better methods are needed to obtain more than 10 mg of G1M9-glycopeptide. In this study, we report the preparation of G1M9-glycopeptide (13.2 mg) linking Asn-Gly-Thr triad as consensus sequence from 40 chicken eggs. In this procedure, λ-carrageenan treatment followed by papain treatment was used to separate the Fc region of IgY antibody that harbors high-mannose glycans. Moreover, cotton hydrophilic interaction liquid chromatography was adapted for easy purification. The resulting G1M9-Asn(Fmoc)-Gly-Thr was identified by nuclear magnetic resonance and mass spectroscopy. G1M9-Asn(Fmoc)-Gly, G1M9-Asn(Fmoc), and G1M9-OH were also detected by mass spectroscopy. Here, our developed G1M9-tripeptide might be useful for the elucidation of glycoprotein functions as well as the specific roles of the consensus sequence.

Protein disulfide isomerase 1 is required for RodA assembling-based conidial hydrophobicity of Aspergillus fumigatus

The hydrophobic layer of Aspergillus conidia, composed of RodA, plays a crucial role in conidia transfer and immune evasion. It self-assembles into hydrophobic rodlets through intramolecular disulfide bonds. However, the secretory process of RodA and its regulatory elements remain unknown. Since protein disulfide isomerase (PDI) is essential for the secretion of many disulfide-bonded proteins, we investigated whether PDI is also involved in RodA secretion and assembly. By gene knockout and phenotypic analysis, we found that Pdi1, one of the four PDI-related proteins of Aspergillus fumigatus, determines the hydrophobicity and integrity of the rodlet layer of the conidia. Preservation of the thioredoxin-active domain of Pdi1 was sufficient to maintain conidial hydrophobicity, suggesting that Pdi1 mediates RodA assembly through its disulfide isomerase activity. In the absence of Pdi1, the disulfide mismatch of RodA in conidia may prevent its delivery from the inner to the outer layer of the cell wall for rodlet assembly. This was demonstrated using a strain expressing a key cysteine-mutated RodA. The dormant conidia of the Pdi1-deficient strain (Δpdi) elicited an immune response, suggesting that the defective conidia surface in the absence of Pdi1 exposes internal immunogenic sources. In conclusion, Pdi1 ensures the correct folding of RodA in the inner layer of conidia, facilitating its secretion into the outer layer of the cell wall and allowing self-assembly of the hydrophobic layer. This study has identified a regulatory element for conidia rodlet assembly.IMPORTANCEAspergillus fumigatus is the major cause of invasive aspergillosis, which is mainly transmitted by the inhalation of conidia. The spread of conidia is largely dependent on their hydrophobicity, which is primarily attributed to the self-assembly of the hydrophobic protein RodA on the cell wall. However, the mechanisms underlying RodA secretion and transport to the outermost layer of the cell wall are still unclear. Our study identified a critical role for Pdi1, a fungal protein disulfide isomerase found in regulating RodA secretion and assembly. Inhibition of Pdi1 prevents the formation of correct S-S bonds in the inner RodA, creating a barrier to RodA delivery and resulting in a defective hydrophobic layer. Our findings provided insight into the formation of the conidial hydrophobic layer and suggested potential drug targets to inhibit A. fumigatus infections by limiting conidial dispersal and altering their immune inertia.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Comparative Quantitative Proteomics Reveals the Desiccation Stress Responses of the Intertidal Seaweed NEOPORPHYRA haitanensis

Neoporphyra haitanensis is an economically important red seaweed that inhabits upper intertidal zones. The thallus tolerates extreme fluctuating environmental stresses (e.g., surviving more than 80% water loss during low tides). To elucidate the global molecular responses relevant to this outstanding desiccation tolerance, a quantitative proteomics analysis of N. haitanensis under different desiccation treatments as well as rehydration was performed. According to the clustering of expression patterns and the functional interpretation of the 483 significantly differentially expressed proteins, a three-stage cellular response to desiccation stress and subsequent rehydration was proposed. Stage I: at the beginning of water loss, multiple signal transduction pathways were triggered including lipid signaling, protein phosphorylation cascades, and histone acetylation controlling acetate biosynthesis to further modulate downstream hormone signaling. Protein protection by peptidyl-prolyl isomerase and ROS scavenging systems were also immediately switched on. Stage II: with the aggravation of stress, increases in antioxidant systems, the accumulation of LEA proteins, and the temporary biosynthesis of branched starch were observed. Multiple enzymes involved in redox homeostasis, including peroxiredoxin, thioredoxin, ascorbate peroxidase, superoxide dismutase, glutathione peroxidase, and glutathione reductase, were hypothesized to function in specific cellular compartments. Stage III: when the desiccated thalli had rehydrated for 30 mins, photosynthesis and carbon fixation were recovered, and antioxidant activities and protein structure protection were maintained at a high level. This work increases the understanding of the molecular responses to environmental stresses via a proteomic approach in red seaweeds and paves the way for further functional studies and genetic engineering.

Identification of membrane proteome of Paracoccidioides lutzii and its regulation by zinc

Aim:

During infection development in the host, Paracoccidioides spp. faces the deprivation of micronutrients, a mechanism called nutritional immunity. This condition induces the remodeling of proteins present in different metabolic pathways. Therefore, we attempted to identify membrane proteins and their regulation by zinc in Paracoccidioides lutzii.

Materials & methods:

Membranes enriched fraction of yeast cells of P. lutzii were isolated, purified and identified by 2D LC–MS/MS detection and database search.

Results & conclusion:

Zinc deprivation suppressed the expression of membrane proteins such as glycoproteins, those involved in cell wall synthesis and those related to oxidative phosphorylation. This is the first study describing membrane proteins and the effect of zinc deficiency in their regulation in one member of the genus Paracoccidioides.

The methodology of protein identification allows the characterization of biological processes performed by those molecules. Therefore, we performed a membrane proteomic analysis of Paracoccidioides lutzii and further evaluated the responses of the fungus to zinc deprivation. The results obtained in the work allowed the characterization of membrane proteins present in organelles that are related to different cellular functions. Zinc deprivation changes processes related to cellular physiology and metabolism. These results help us to understand the process of pathogen–host interaction, since zinc deprivation is a condition present during infection.