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Proposed model for dolichol biosynthesis in budding yeast, Saccharomyces cerevisiae.
Image Credit: Kazuki Hanaoka, Kuya Matsunaga, et al. PNAS. May 27, 2026
Scientific Frontline: Extended "At a Glance" Summary: Dolichol Biosynthesis in Eukaryotes
The Core Concept: Dolichol is a vital lipid required for protein glycosylation, a process essential for protein function across all eukaryotic life. Recent research confirms that the three-step "detour" pathway for its biosynthesis is not exclusive to humans but is an evolutionarily conserved mechanism found in organisms as simple as budding yeast.
Key Distinction/Mechanism: Unlike the previously held view that dolichol is synthesized via a single-step reduction of polyprenol by a single enzyme (DFG10 in yeast/SRD5A3 in humans), cells utilize a more complex, overlapping biochemical system. This includes a three-step detour pathway involving the gene TDA5 (the yeast equivalent of human DHRSX) operating in parallel with the primary reduction pathway.
Major Frameworks/Components:
- SRD5A3/DFG10 Pathway: The primary, canonical reduction process for dolichol production.
- TDA5/DHRSX Detour Pathway: An evolutionarily conserved three-step alternative route that operates in parallel to the canonical pathway.
- Backup Biosynthesis: Evidence from double-deletion mutant studies (DFG10/TDA5) indicates the existence of at least one additional, as-yet-unidentified compensatory pathway for dolichol production.
- Chromatographic Analysis: The methodology used to measure levels of dolichol and polyprenol in wild-type and mutant yeast strains.
Branch of Science: Biochemistry, Molecular Biology, Evolutionary Biology, Genetics.
Future Application: Continued identification of the "backup" pathway components could provide deep insights into cellular resilience. Mapping these pathways is a necessary precursor to understanding and potentially developing therapeutic interventions for Congenital Disorders of Glycosylation (CDGs).
Why It Matters: Establishing that these biosynthetic pathways are conserved across eukaryotes clarifies a fundamental biological process. Understanding these mechanisms is critical for addressing the etiology of rare genetic diseases related to abnormal protein glycan modification.
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| Relative dolichol and polyprenol levels in wild-type, DFG10 deletion mutants, TDA5 deletion mutants, and DFG10-TDA5 double deletion mutants. Image Credit: Kazuki Hanaoka, Kuya Matsunaga, et al. PNAS. May 27, 2026 |
Hiroshima University researchers say a newly proposed three-step “detour” pathway for making dolichol, a molecule cells need to properly process proteins, may be more universal than scientists realized. Experiments in yeast suggest eukaryotes may rely on overlapping biochemical pathways, including the evolutionarily conserved “detour” and evidence of a possible “backup route,” to produce a molecule essential to life.
Dolichol is an essential lipid in eukaryotic cells. It is required for protein glycosylation, which is the addition of carbohydrates to proteins. This process is vital for a variety of protein functions. Defects in the synthesis of dolichol lead to congenital disorders of glycosylation (CDGs), a large group of rare genetic disorders that are treatable but incurable.
A research team at Hiroshima University has provided evidence for the evolutionary conservation of a three-step synthesis pathway for dolichol in yeast. This discovery supports the view that multiple dolichol biosynthesis pathways are evolutionarily conserved across eukaryotes.
Previously, scientists believed that dolichol was synthesized by a single-step reduction of polyprenol. The gene encoding the enzyme that catalyzes this reaction is SRD5A3 in humans and DFG10 in budding yeast (Saccharomyces cerevisiae). Research from 2024 revealed that this understanding was incomplete, and researchers proposed a three-step detour pathway for dolichol biosynthesis in humans involving the gene DHRSX.
Because genes corresponding to DHRSX had not been identified in yeast, it remained unknown whether the detour pathway was conserved in yeast and other eukaryotes, or whether it was unique to humans.
The researchers set out to settle the question by focusing on mutation studies of enzymes in yeast belonging to the short-chain dehydrogenase/reductase (SDR) superfamily, to which DHRSX belongs. Of the thirteen genes they examined, two genes—TDA5 and ENV9—were identified as being involved with dolichol biosynthesis, with TDA5 being more directly associated than ENV9.
Further experiments showed that TDA5 serves the same function as DHRSX in yeast; moreover, the role it plays is separate from that of DFG10. Their observations also revealed that TDA5 and DFG10 may act in parallel rather than sequentially.
“What we most want to convey is that the recently proposed ‘three-step dolichol biosynthesis bypass pathway’ is not a mechanism unique to humans, but is also conserved in budding yeast, making it a fundamental biological system common to all eukaryotes,” says Kouichi Funato, a professor at Hiroshima University’s Graduate School of Integrated Sciences for Life and corresponding author of the paper.
Researchers conducted a detailed analysis of dolichol and polyprenol levels in wild-type and mutant yeast using chromatography. In wild-type yeast, dolichol was predominant, and polyprenol was undetectable. DFG10 deletion mutants showed increased polyprenol levels. TDA5 deletion mutants showed significantly increased polyprenol and severely reduced dolichol levels. Surprisingly, in DFG10-TDA5 double deletion mutants, while polyprenol levels were double those of TDA5 deletion mutants, dolichol levels were also doubled.
“Even when TDA5 and DFG10 were both knocked out simultaneously, dolichol did not completely disappear. This suggests the possibility that cells retain a ‘backup pathway,’ separate from the three-step detour pathway that requires TDA5 and DFG10, to support dolichol biosynthesis,” Funato explains.
“The next step is to elucidate the nature of this ‘alternative pathway,’ which we believe exists independently of the three-step detour pathway. We suspect that this pathway may involve as-yet-unidentified factors,” Funato concludes. “Ultimately, our goal is to elucidate the complete picture of dolichol biosynthesis and lay the groundwork for explaining how abnormalities in glycan modification lead to cellular dysfunction and disease.”
Kazuki Hanaoka, Kuya Matsunaga, Souichirou Shimizu, and Soshi Sakai at Hiroshima University, as well as Harald Pichler at Graz University of Technology and the Austrian Centre of Industrial Biotechnology GmbH, contributed to this study. Kazuki Hanaoka and Kuya Matsunaga were joint first authors of the study.
Funding: This work was supported by the Japan Society for the Promotion of Science (JSPS) Grants-in-Aid for Scientific Research (KAKENHI; 21K19088).
Published in journal: Proceedings of the National Academy of Sciences
Authors: Kazuki Hanaoka, Kuya Matsunaga, Souichirou Shimizu, Soshi Sakai, Harald Pichler, and Kouichi Funato
Source/Credit: Hiroshima University
Edited by: Scientific Frontline
Reference Number: bchm060826_01
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