New Study Traces Human N-Glycosylation Evolution

A new study published in Engineering examines the evolutionary history of the human N-glycosylation pathway, essential for protein modification. Researchers from institutions in Croatia, including the University of Zagreb and the Ruder Bošković Institute, applied phylostratigraphy to track glycosylation machinery (GM) genes and glycoproteins (GPs) across a wide phylogenetic range.

Glycosylation attaches glycans enzymatically to proteins, lipids, or RNA as a common post-translational modification in humans. It supports key biological roles such as cell signaling, immune response, and protein stability. Prior to this work, the evolutionary origins of glycosylation were largely unexplored.

Most human GM genes originated during two pivotal periods: the start of all cellular organisms and the rise of eukaryotes. This points to glycosylation as an ancient mechanism shared across life forms, with notable expansion in early eukaryotes. In comparison, GPs showed strong presence in later phases, particularly from metazoans to vertebrates.

The analysis centered on the N-glycosylation (NG) pathway, active mainly in the endoplasmic reticulum (ER) and Golgi apparatus. Cytoplasmic-side ER NG genes largely date to cellular organism origins, while ER lumen-facing ones emerged with eukaryotes. This split implies the ER formed via invagination of a prokaryotic cell membrane holding an NG pathway.

Investigators assembled a full catalog of GM genes and GPs from sources like the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the Carbohydrate Active enZYmes (CAZY) database. They built a consensus phylogeny spanning 503 organisms from cellular beginnings to humans, then used the blastp algorithm to assign origins across 29 phylostrata.

Findings indicate 56% of GM genes link to cellular organism origins, 24% to eukaryotic origins, and 17% to the Amorphea-to-Bilateria interval, underscoring glycosylation's role in animal multicellularity. In the ER, prokaryotic-origin GM genes cluster on the cytoplasmic side, with eukaryotic ones on the luminal side, backing the membrane invagination model. The Golgi mirrors this: glycosidases mainly cellular in origin, glycosyltransferases eukaryotic.

These patterns illuminate glycosylation's deep history and set the stage for glycomics research with medical potential. Insights into pathway origins may clarify disease processes and inform targeted therapies.