A new study published in Engineering provides significant insights into the evolutionary history of the human N-glycosylation pathway, a critical process in protein modification. Researchers from various institutions in Croatia, including the University of Zagreb and the Ruder Bošković Institute, utilized phylostratigraphy to trace the origins of glycosylation machinery (GM) genes and glycoproteins (GPs) across a broad phylogenetic context.

Glycosylation, the enzymatic process of attaching glycans to proteins, lipids, or RNA, is a common post-translational modification in humans. It plays a crucial role in various biological functions, including cell signaling, immune response, and protein stability. Despite its importance, the evolutionary origins of glycosylation have remained largely unexplored until now.

The study found that the majority of human GM genes can be traced back to two key evolutionary periods: the origin of all cellular organisms and the origin of eukaryotes. This suggests that glycosylation is an ancient process, likely common to all life forms, and was further elaborated in early eukaryotes. In contrast, GPs showed significant enrichment in more recent evolutionary periods, highlighting their importance in the transition from metazoans to vertebrates.

Specifically, the research focused on the N-glycosylation (NG) pathway, which occurs primarily in the endoplasmic reticulum (ER) and the Golgi apparatus. The findings revealed a striking evolutionary pattern: the NG genes acting on the cytoplasmic side of the ER predominantly trace back to the origin of cellular organisms, while those oriented toward the ER lumen are of eukaryotic origin. This binary evolutionary origin suggests that the ER may have evolved through the invagination of a prokaryotic cell membrane containing an NG pathway.

The researchers compiled a comprehensive list of GM genes and GPs, utilizing data from multiple sources, including the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the Carbohydrate Active enZYmes (CAZY) database. They constructed a consensus phylogeny of 503 organisms, representing major lineages from the origin of cellular organisms to humans. Using the blastp algorithm, they mapped the evolutionary origins of these genes across 29 phylogenetic levels, known as phylostrata.

The results showed that 56% of GM genes mapped to the origin of cellular organisms, indicating that glycosylation is an ancient process shared by all life forms. Another 24% of GM genes were traced to the origin of eukaryotes, suggesting significant evolutionary innovations during this period. Additionally, 17% of GM genes were mapped to the period between the origin of Amorphea and Bilateria, highlighting the importance of glycosylation in the development of animal multicellularity.

In the ER, the study found that GM genes of prokaryotic origin were primarily located on the cytoplasmic side, while those of eukaryotic origin were found on the luminal side. This spatial distribution supports the hypothesis that the ER evolved from the invagination of a prokaryotic membrane. In the Golgi apparatus, a similar binary evolutionary origin was observed, with glycosidases predominantly of cellular origin and glycosyltransferases of eukaryotic origin.

The findings of this study not only shed light on the evolutionary history of glycosylation but also provide a foundation for future research in glycomics and its applications in medicine. Understanding the origins and evolution of glycosylation pathways could lead to new insights into disease mechanisms and the development of targeted therapies.

The paper “Contrasting Macroevolutionary Patterns in the Human N-Glycosylation Pathway,” is authored by Domagoj Kifer, Nina Čorak, Mirjana Domazet-Lošo, Niko Kasalo, Gordan Lauc, Göran Klobučar, Tomislav Domazet-Lošo. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.06.039. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.