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Multiple isoforms of malic enzyme in the oleaginous fungus, Mortierella alpina

Ying Zhang1, Colin Ratledge

  • 1Department of Biological Sciences, University of Hull, Hull, UK.

Mycological Research
|May 21, 2008
PubMed

Insights

Malic enzyme (ME) is crucial for fatty acid synthesis in fungi. Researchers identified seven ME isoforms in Mortierella alpina, with isoform E linked to lipid accumulation under nitrogen depletion.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Microbiology

Background:

  • Malic enzyme (ME) is essential for providing NADPH for fatty acid biosynthesis in oleaginous microorganisms.
  • ME may exist in multiple forms, potentially encoded by different genes, to fulfill various cellular roles.

Purpose of the Study:

  • To identify and characterize different isoforms of malic enzyme in the oleaginous fungus Mortierella alpina.
  • To investigate the association of specific ME isoforms with cellular conditions like lipid accumulation and oxygen availability.

Main Methods:

  • Non-denaturing polyacrylamide gel electrophoresis (PAGE) was used to separate protein extracts from Mortierella alpina.
  • Specific activity staining was employed to visualize and identify different malic enzyme isoforms.
  • Cellular conditions, including nitrogen availability and oxygen levels, were manipulated during growth.

Main Results:

  • Seven malic enzyme (ME) isoforms (A-G) were identified in Mortierella alpina.
  • Isoform E, derived from isoform D, was specifically associated with lipid accumulation under nitrogen-depleted conditions.
  • Isoforms A, B, C, F, and G were linked to oxygen-limited growth, while D and E appeared under both aerobic and anaerobic conditions.
  • Isoform E was observed to convert to isoform G during cold storage, suggesting post-transcriptional modification.

Conclusions:

  • Mortierella alpina possesses multiple malic enzyme isoforms with distinct physiological roles.
  • Isoform E plays a key role in lipid accumulation, regulated by nitrogen availability.
  • The existence of multiple isoforms and potential post-transcriptional modifications highlight the complex regulation of malic enzyme in oleaginous fungi.

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