Dolichol, a vital lipid molecule embedded in eukaryotic cellular membranes, plays an indispensable role in protein glycosylation—the enzymatic and structural modification of proteins through carbohydrate addition. This glycosylation is paramount for proper protein folding, stability, and function. Intriguingly, disruptions in dolichol synthesis give rise to congenital disorders of glycosylation (CDGs), a heterogeneous group of rare genetic diseases characterized by diverse but severe physiological impairments. Although CDGs remain incurable, their treatability motivates ongoing efforts to understand the molecular basis of dolichol biosynthesis.

Historically, the biosynthetic pathway of dolichol was considered a straightforward, single-step biochemical reaction involving the reduction of polyprenol molecules. This reduction is catalyzed by the enzyme encoded by the human gene SRD5A3 and its homolog DFG10 in budding yeast. However, a pivotal study in 2024 revealed the inadequacy of this simplistic model. It proposed a more intricate “three-step detour” enzymatic pathway for dolichol biosynthesis in humans, emphasizing the role of the gene DHRSX. The revelation of this alternative route opened new questions regarding its evolutionary distribution across eukaryotes, given that yeast genomes appeared devoid of direct DHRSX orthologs.

Addressing this paradox, the Hiroshima University research collective embarked on an ambitious quest to identify yeast genetic elements analogously fulfilling DHRSX functions. Their investigation concentrated on the short-chain dehydrogenase/reductase (SDR) superfamily, within which DHRSX resides. Mutational analysis of thirteen SDR genes revealed that two—TDA5 and ENV9—participate directly in dolichol biosynthesis. Among these, TDA5 demonstrated a more profound involvement, effectively paralleling human DHRSX’s enzymatic function.

Subsequent biochemical and genetic assays illuminated a nuanced picture: TDA5 operates independently of the canonical yeast dolichol reductase DFG10, indicating that budding yeast possess parallel pathways for dolichol production. These findings denote a conserved evolutionary architecture wherein a three-step detour pathway, previously deemed a human-exclusive adaptation, also prevails in single-celled eukaryotes—a revelation poised to redefine foundational concepts in lipid biology.

Quantitative chromatographic measurements of dolichol and its immediate precursor, polyprenol, underscored the functional interplay between TDA5 and DFG10. Wild-type yeast strains exhibited a predominance of dolichol with an absence of detectable polyprenol, whereas deletion mutants lacking DFG10 showed an accumulation of the precursor polyprenol. More strikingly, mutants deficient in TDA5 accumulated polyprenol at even higher levels while simultaneously displaying a stark reduction in dolichol, underscoring TDA5’s critical role.

A particularly intriguing observation emerged from strains bearing simultaneous deletions in both TDA5 and DFG10. These double mutants manifested increased polyprenol levels that doubled those found in TDA5 single mutants, yet paradoxically, dolichol levels also unexpectedly doubled. This anomaly points to the existence of a previously unidentified “backup pathway” or compensatory mechanism operational in yeast, ensuring dolichol biosynthesis continuity even when both primary pathways are compromised.

The identification of this alternative route raises compelling biological questions, especially concerning its molecular constituents and regulatory dynamics. The investigative team postulates that this backup pathway likely involves yet-to-be-characterized enzymes or cofactors, which may act independently from the known three-step detour and canonical reduction pathways. Deciphering this pathway holds tremendous promise not only for fundamental biology but also for medical science, as defects in these mechanisms underpin disorders involving protein glycosylation.

Professor Kouichi Funato, lead investigator and corresponding author from Hiroshima University’s Graduate School of Integrated Sciences for Life, emphasizes the broad significance of these findings. He asserts that the conservation of the detour pathway across distant eukaryotes like yeast and humans underscores its foundational biological importance. This universality hints at an ancient evolutionary origin for complex dolichol biosynthesis mechanisms, essential for life’s molecular machinery.

Future research aims to map the alternative dolichol biosynthesis pathway comprehensively. Understanding how these overlapping and backup mechanisms coordinate, interact, and respond to genetic or environmental perturbations may illuminate new therapeutic targets for CDGs. Moreover, elucidating the full spectrum of enzymes and intermediates involved could provide critical insights into the regulation of glycan modifications and their implications in cellular dysfunction.

This study complements and advances prior knowledge by integrating genetic, biochemical, and evolutionary approaches to tackle previously intractable questions. The multidisciplinary team, including Kazuki Hanaoka and Kuya Matsunaga as joint first authors, alongside collaborators from Graz University of Technology and the Austrian Centre of Industrial Biotechnology GmbH, exemplifies the collaborative spirit necessary for such scientific breakthroughs.

Supported by the Japan Society for the Promotion of Science (JSPS) under Grant number 21K19088, this research exemplifies the synergy between international cooperation and cutting-edge experimental methodologies. It marks a pivotal milestone in molecular cell biology and sets the stage for future discoveries poised to transform our understanding of cellular lipid metabolism and its broader biomedical relevance.

Subject of Research: Cells

Article Title: The revised three-step detour pathway in dolichol biosynthesis is evolutionarily conserved in budding yeast

News Publication Date: 27-May-2026

Web References:
PNAS Article DOI: 10.1073/pnas.2613147123

References:
Hanaoka, K., Matsunaga, K., Shimizu, S., Sakai, S., Pichler, H., & Funato, K. (2026). The revised three-step detour pathway in dolichol biosynthesis is evolutionarily conserved in budding yeast. Proceedings of the National Academy of Sciences, May 27, 2026.

Image Credits: Kazuki Hanaoka, Kuya Matsunaga, et al. / PNAS / May 27, 2026

Keywords: Dolichol biosynthesis, protein glycosylation, Saccharomyces cerevisiae, evolutionary conservation, three-step detour pathway, short-chain dehydrogenase/reductase, SDR superfamily, congenital disorders of glycosylation, backup pathway, lipid metabolism, cellular biochemistry