Lipid metabolism research in oleaginous fungus Mortierella alpina: Current progress and future prospects

ABSTRACTMortierella alpinais a filamentous fungus commonly found in soil that is able to produce lipids in the form of triacylglycerols that account for up to 50% of its dry weight. Analysis of theM. alpinagenome suggests that there is a phenylalanine-hydroxylating system for the catabolism of phenylalanine, which has never been found in fungi before. We characterized the phenylalanine-hydroxylating system inM. alpinato explore its role in phenylalanine metabolism and its relationship to lipid biosynthesis. Significant changes were found in the profile of fatty acids inM. alpinagrown on medium containing an inhibitor of the phenylalanine-hydroxylating system compared toM. alpinagrown on medium without inhibitor. Genes encoding enzymes involved in the phenylalanine-hydroxylating system (phenylalanine hydroxylase [PAH], pterin-4α-carbinolamine dehydratase, and dihydropteridine reductase) were expressed heterologously inEscherichia coli, and the resulting proteins were purified to homogeneity. Their enzymatic activity was investigated by high-performance liquid chromatography (HPLC) or visible (Vis)-UV spectroscopy. Two functional PAH enzymes were observed, encoded by distinct gene copies. A novel role for tetrahydrobiopterin in fungi as a cofactor for PAH, which is similar to its function in higher life forms, is suggested. This study establishes a novel scheme for the fungal degradation of an aromatic substance (phenylalanine) and suggests that the phenylalanine-hydroxylating system is functionally significant in lipid metabolism.

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Role of Malic Enzyme during Fatty Acid Synthesis in the Oleaginous Fungus Mortierella alpina

Applied and Environmental Microbiology ◽

10.1128/aem.00140-14 ◽

2014 ◽

Vol 80 (9) ◽

pp. 2672-2678 ◽

Cited By ~ 57

Author(s):

G. Hao ◽

H. Chen ◽

L. Wang ◽

Z. Gu ◽

Y. Song ◽

...

Keyword(s):

Fatty Acid ◽

Fatty Acid Synthesis ◽

Malic Enzyme ◽

Acid Synthesis ◽

Mortierella Alpina ◽

Oleaginous Fungus

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Biochemical characterization of the tetrahydrobiopterin synthesis pathway in the oleaginous fungus Mortierella alpina

Microbiology ◽

10.1099/mic.0.051847-0 ◽

2011 ◽

Vol 157 (11) ◽

pp. 3059-3070 ◽

Cited By ~ 16

Author(s):

Hongchao Wang ◽

Bo Yang ◽

Guangfei Hao ◽

Yun Feng ◽

Haiqin Chen ◽

...

Keyword(s):

Biochemical Characterization ◽

De Novo ◽

Mortierella Alpina ◽

Recombinant Enzymes ◽

Homologous Proteins ◽

Genes Encoding ◽

Oleaginous Fungus ◽

Cell Processes ◽

Common Substrate

We characterized the de novo biosynthetic pathway of tetrahydrobiopterin (BH4) in the lipid-producing fungus Mortierella alpina. The BH4 cofactor is essential for various cell processes, and is probably present in every cell or tissue of higher organisms. Genes encoding two copies of GTP cyclohydrolase I (GTPCH-1 and GTPCH-2) for the conversion of GTP to dihydroneopterin triphosphate (H2-NTP), 6-pyruvoyltetrahydropterin synthase (PTPS) for the conversion of H2-NTP to 6-pyruvoyltetrahydropterin (PPH4), and sepiapterin reductase (SR) for the conversion of PPH4 to BH4, were expressed heterologously in Escherichia coli. The recombinant enzymes were produced as His-tagged fusion proteins and were purified to homogeneity to investigate their enzymic activities. Enzyme products were analysed by HPLC and electrospray ionization-MS. Kinetic parameters and other properties of GTPCH, PTPS and SR were investigated. Physiological roles of BH4 in M. alpina are discussed, and comparative analyses between GTPCH, PTPS and SR proteins and other homologous proteins were performed. The presence of two functional GTPCH enzymes has, as far as we are aware, not been reported previously, reflecting the unique ability of this fungus to synthesize both BH4 and folate, using the GTPCH product as a common substrate. To our knowledge, this study is the first to report the comprehensive characterization of a BH4 biosynthesis pathway in a fungus.

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The role of phenylalanine hydroxylase in lipogenesis in the oleaginous fungus Mortierella alpina

Microbiology ◽

10.1099/mic.0.001062 ◽

2021 ◽

Vol 167 (8) ◽

Author(s):

Hongchao Wang ◽

Chunmei Wang ◽

Weiwei Yuan ◽

Haiqin Chen ◽

Wenwei Lu ◽

...

Keyword(s):

Fatty Acid Biosynthesis ◽

Phenylalanine Hydroxylase ◽

Transcript Level ◽

Cellular Fatty Acid ◽

Industrial Applications ◽

Mortierella Alpina ◽

Limiting Factor ◽

Wide Range ◽

Oleaginous Fungus

Phenylalanine hydroxylase (PAH) catalyses the irreversible hydroxylation of phenylalanine to tyrosine, which is the rate-limiting reaction in phenylalanine metabolism in animals. A variety of polyunsaturated fatty acids can be synthesized by the lipid-producing fungus Mortierella alpina, which has a wide range of industrial applications in the production of arachidonic acid. In this study, RNA interference (RNAi) with the gene PAH was used to explore the role of phenylalanine hydroxylation in lipid biosynthesis in M. alpina. Our results indicated that PAH knockdown decreased the PAH transcript level by approximately 55% and attenuated cellular fatty acid biosynthesis. Furthermore, the level of NADPH, which is a critical reducing agent and the limiting factor in lipogenesis, was decreased in response to PAH RNAi, in addition to the downregulated transcription of other genes involved in NADPH production. Our study indicates that PAH is part of an overall enzymatic and regulatory mechanism supplying NADPH required for lipogenesis in M. alpina.

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