A novel fission yeast platform to model N-glycosylation and the bases of congenital disorders of glycosylation Type I

Mechanical effect of protein glycosylation on BiP-mediated post-translational translocation and folding in the endoplasmic reticulum

About one-third of the proteins synthesized in eukaryotic cells are directed to the secretory pathway, where close to 70% are being N-glycosylated. N-glycosylation is a crucial modification for various cellular processes, including endoplasmic reticulum (ER) glycoprotein folding quality control, lysosome delivery, and cell signaling. The defects in N-glycosylation can lead to severe developmental diseases. For the proteins to be glycosylated, they must be translocated to the ER through the Sec61 translocon channel, either via co-translationally or post-translationally. N-glycosylation not only could accelerate post-translational translocation but may also enhance protein stability, while protein folding can assist in their movement into the ER. However, the precise mechanisms by which N-glycosylation and folding influence translocation remain poorly understood. The chaperone BiP is essential for post-translational translocation, using a "ratchet" mechanism to facilitate protein entry into the ER. Although research has explored how BiP interacts with protein substrates, there has been less focus on its binding to glycosylated substrates. Here, we review the effect of N-glycosylation on protein translocation, employing single-molecule studies and ensembles approaches to clarify the roles of BiP and N-glycosylation in these processes. Our review explores the possibility of a direct relationship between translocation and a ratchet effect of glycosylation and the importance of BiP in binding glycosylated proteins for the ER quality control system.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12551-025-01313-x.

Transcriptomics as a predictor of biopharmaceutically favourable glycan profiles

N-glycosylation plays a crucial role in defining the pharmacological properties and efficacy of therapeutic proteins, commonly referred to as biologics. The inherent complexity and lack of a templated process in glycosylation leads to a wide variation in glycan structures, posing significant challenges in achieving consistent glycan profiles on biologics. This study leverages omics technologies to predict which cell lines are likely to yield optimal glycosylation profiles, based on the existing knowledge of the functional impact of specific glycan structures on the pharmacokinetics, immunogenicity, and stability of therapeutic antibodies. The study highlights that bulk RNA-sequencing data holds predictive power for glycosylation outcomes in of monoclonal antibodies (mAbs). For instance, Alg5 is identified to be predictive, before beginning a mAb production run, of mAbs bearing higher levels of Man5. This is inferred to increase glycosylation site occupancy on endogenous proteins, thereby intensifying competition for glycosylation enzymes in the Golgi and indirectly influencing mAb glycan processing. Additionally, the elevation of the UDP-Gal transporter in cell lines expressing mAbs with a single galactose residue is also observed intranscriptomic data prior to beginning a production run. These findings suggest that early-stage transcriptomics can aid in the streamlined development of cell lines by enabling pre-emptive adjustments to enhance glycosylation. The study also underscores that while transcriptomic data can predict certain glycosylation trends, more crucial factors affecting glycan profiles, such as enzyme localization within the Golgi apparatus and endogenous competition for glycosylation machinery, are not captured within the transcriptomic data. These findings suggest that while transcriptomics provides valuable insights, enzyme localization and intracellular dynamics are critical determinants of glycosylation outcomes. Our study starts to address the relevant mechanisms essential for improving cell line development strategies and achieving consistent glycosylation in biologics production.

Intercompatibility of eukaryotic and Asgard archaea ribosome-translocon machineries

In all domains of life, the ribosome-translocon complex inserts nascent transmembrane proteins into, and processes and transports signal peptide-containing proteins across, membranes. Eukaryotic translocons are anchored in the endoplasmic reticulum, while the prokaryotic complexes reside in cell membranes. Phylogenetic analyses indicate the inheritance of eukaryotic Sec61/oligosaccharyltransferase/translocon-associated protein translocon subunits from an Asgard archaea ancestor. However, the mechanism for translocon migration from a peripheral membrane to an internal cellular compartment (the proto-endoplasmic reticulum) during eukaryogenesis is unknown. Here we show compatibility between the eukaryotic ribosome-translocon complex and Asgard signal peptides and transmembrane proteins. We find that Asgard translocon proteins from Candidatus Prometheoarchaeum syntrophicum strain Candidatus Prometheoarchaeum syntrophicum strain MK-D1, a Lokiarchaeon confirmed to contain no internal cellular membranes, are targeted to the eukaryotic endoplasmic reticulum on ectopic expression. Furthermore, we show that the cytoplasmic domain of Candidatus Prometheoarchaeum syntrophicum strain MK-D1 oligosaccharyltransferase 1 (ribophorin I) can interact with eukaryotic ribosomes. Our data indicate that the location of existing ribosome-translocon complexes, at the protein level, determines the future placement of yet-to-be-translated translocon subunits. This principle predicts that during eukaryogenesis, under positive selection pressure, the relocation of a few translocon complexes to the proto-endoplasmic reticulum will have contributed to propagating the new translocon location, leading to their loss from the cell membrane.

"Autophagic landscapes: on the paradox of survival through self-degradation" - a science-inspired exhibition

The Complexity Science Hub Vienna is hosting an autophagy-based art exhibition that shows the artwork by Ayelen Valko and Dorotea Fracchiolla, two artists who are also scientists engaged in autophagy research. This exhibition, called "Autophagic landscapes: on the paradox of survival through self-degradation"-which will be open to the general public from January to May 2023-proposes a visual journey from entire organisms toward the interior of a single cell. The core ideas represented in the exhibited artworks are the molecular mechanisms and vesicular dynamics of autophagy-two phenomena that have been feeding the imagination of the two artists, inspiring the creation of art that depicts intriguing subcellular landscapes. Although the microscale bears very valuable aesthetic features, it is not a common subject in art. Correcting this is the main aim of this exhibition and of the two artists.

Humanization of Yeasts for Glycan-Type End-Products

Yeasts are often considered microorganisms for producing human therapeutic glycosylated end-products at an industrial scale. However, the products with non-humanized glycans limited their usage. Therefore, various methods to develop humanized glycosylated end-products have been widely reported in yeasts. To make full use of these methods, it is necessary to summarize the present research to find effective approaches to producing humanized products. The present research focuses on yeast species selection, glycosyltransferase deletion, expression of endoglycosidase, and expression of proteins with galactosylated and or sialylated glycans. Nevertheless, the yeasts will have growth defects with low bioactivity when the key enzymes are deleted. It is necessary to express the corresponding repairing protein. Compared with N-glycosylation, the function of yeast protein O-glycosylation is not well-understood. Yeast proteins have a wide variety of O-glycans in different species, and it is difficult to predict glycosylation sites, which limits the humanization of O-glycosylated yeast proteins. The future challenges include the following points: there are still many important potential yeasts that have never been tried to produce glycosylated therapeutic products. Their glycosylation pathway and related mechanisms for producing humanized glycosylated proteins have rarely been reported. On the other hand, the amounts of key enzymes on glycan pathways in human beings are significantly more than those in yeasts. Therefore, there is still a challenge to produce a large body of humanized therapeutic end-products in suitable yeast species, especially the protein with complex glycans. CRISPR-Cas9 system may provide a potential approach to address the important issue.

First person – Giovanna Lucrecia Gallo and Ayelen Valko

First Person is a series of interviews with the first authors of a selection of papers published in Journal of Cell Science, helping early-career researchers promote themselves alongside their papers. Giovanna Lucrecia Gallo and Ayelen Valko are co-first authors on ‘ A novel fission yeast platform to model N-glycosylation and the bases of congenital disorders of glycosylation type I’, published in JCS. Giovanna conducted the research described in this article while a PhD student in Cecilia D'Alessio's lab at Fundación Instituto Leloir, Buenos Aires, Argentina. She is now a postdoc in the lab of Nora Lopez at Centro de Virologia Humana y Animal, Buenos Aires, Argentina, investigating the biological mechanisms underlying virus–host cell interactions, intracellular viral strategies to survive host immune responses and the control mechanisms displayed by the host. Ayelen conducted the research described in this article while a postdoc in Cecilia D'Alessio's lab. She is now a postdoc in the lab of Sebastian Schuck at Heidelberg University Biochemistry Center, Germany, investigating the underlying mechanisms of micro-ER-phagy, an autophagic process that is essential for elimination of the ER during ER stress.