Squalene monooxygenase

Squalene epoxidase
File:Cholesterol-Synthesis-Reaction11.png Chemical reaction catalyzed by squalene epoxidase.
Identifiers
EC number	1.14.13.132
CAS number	9029-62-3
Databases
IntEnz	IntEnz view
BRENDA	BRENDA entry
ExPASy	NiceZyme view
KEGG	KEGG entry
MetaCyc	metabolic pathway
PRIAM	profile
PDB structures	RCSB PDB PDBe PDBsum
Gene Ontology	AmiGO / QuickGO
Search PMC articles PubMed articles NCBI proteins

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Identifiers
Aliases
External IDs	GeneCards: [1]
Orthologs
Species	Human	Mouse
Entrez	n/a	n/a
Ensembl	n/a	n/a
UniProt	n/a	n/a
RefSeq (mRNA)	n/a	n/a
RefSeq (protein)	n/a	n/a
Location (UCSC)	n/a	n/a
PubMed search	n/a	n/a
Wikidata
View/Edit Human

Squalene monooxygenase (also called squalene epoxidase) is an enzyme that uses NADPH and molecular oxygen to oxidize squalene to 2,3-oxidosqualene (squalene epoxide). Squalene epoxidase catalyzes the first oxygenation step in sterol biosynthesis and is thought to be one of the rate-limiting enzymes in this pathway. In humans, squalene epoxidase is encoded by the SQLE gene. Several eukaryote genomess lack a squalene monooxygenase encoding gene, but instead encode an alternative squalene epoxidase that catalyzes the oxidation of squalene.

Mechanism

The canonical squalene monooxygenase is a flavoprotein monooxygenase. Flavoprotein monooxygenase form flavin hydroperoxides at the enzyme active site, which then transfer the terminal oxygen atom of the hydroperoxide to the substrate. Squalene monooxygenase differs from other flavin monooxygenases in that the oxygen is inserted as an epoxide rather than as a hydroxyl group. Squalene monooxygenase contains a loosely bound FAD flavin and obtains electrons from NADPH-cytochrome P450 reductase, rather than binding the nicotinamide cofactor NADPH directly. The alternative squalene epoxidase belongs to the fatty acid hydroxylase superfamily and obtains electrons from cytochrome b5.

Inhibitors

Inhibitors of squalene epoxidase have found application mainly as antifungal drugs:

• butenafine
• naftifine
• terbinafine

Since squalene epoxidase is on the biosynthetic pathway leading to cholesterol, inhibitors of this enzyme may also find application in treatment of hypercholesterolemia.

Localization

In yeast Saccharomyces cerevisiae, squalene epoxidase is localized to both the endoplasmic reticulum and lipid droplets. Only the ER localized protein is active.

Additional products

Squalene epoxidase also catalyzes the formation of diepoxysqualene (DOS). DOS is converted to 24(S),25-epoxylanosterol by lanosterol synthase.

Model organisms

Model organisms have been used in the study of SQLE function. A conditional knockout mouse line called Sqle^{tm1a(EUCOMM)Wtsi} was generated at the Wellcome Trust Sanger Institute. Male and female animals underwent a standardized phenotypic screen to determine the effects of deletion. Additional screens performed: - In-depth immunological phenotyping

Sqle knockout mouse phenotype

Characteristic	Phenotype
All data available at.
Peripheral blood leukocytes 6 Weeks	Normal
Insulin	Normal
Haematology 6 Weeks	Normal
Homozygous viability at P14	Abnormal
Recessive lethal study	Abnormal
Body weight	Normal
Neurological assessment	Normal
Grip strength	Normal
Dysmorphology	Normal
Indirect calorimetry	Normal
Glucose tolerance test	Normal
Auditory brainstem response	Normal
DEXA	Normal
Radiography	Normal
Eye morphology	Normal
Clinical chemistry	Normal
Haematology 16 Weeks	Normal
Peripheral blood leukocytes 16 Weeks	Normal
Heart weight	Normal
Salmonella infection	Normal
Cytotoxic T Cell Function	Normal
Spleen Immunophenotyping	Normal
Mesenteric Lymph Node Immunophenotyping	Normal
Bone Marrow Immunophenotyping	Normal
Epidermal Immune Composition	Normal

See also

• Antifungal drug#Allylamines

Further reading

• Ma J, Dempsey AA, Stamatiou D, Marshall KW, Liew CC (Mar 2007). "Identifying leukocyte gene expression patterns associated with plasma lipid levels in human subjects". Atherosclerosis. 191 (1): 63–72. doi:10.1016/j.atherosclerosis.2006.05.032. PMID 16806233.
• Laden BP, Tang Y, Porter TD (Feb 2000). "Cloning, heterologous expression, and enzymological characterization of human squalene monooxygenase". Archives of Biochemistry and Biophysics. 374 (2): 381–8. doi:10.1006/abbi.1999.1629. PMID 10666321.
• Helms MW, Kemming D, Pospisil H, Vogt U, Buerger H, Korsching E, Liedtke C, Schlotter CM, Wang A, Chan SY, Brandt BH (Sep 2008). "Squalene epoxidase, located on chromosome 8q24.1, is upregulated in 8q+ breast cancer and indicates poor clinical outcome in stage I and II disease". British Journal of Cancer. 99 (5): 774–80. doi:10.1038/sj.bjc.6604556. PMC 2528137. PMID 18728668.
• Nagai M, Sakakibara J, Nakamura Y, Gejyo F, Ono T (Jul 2002). "SREBP-2 and NF-Y are involved in the transcriptional regulation of squalene epoxidase". Biochemical and Biophysical Research Communications. 295 (1): 74–80. doi:10.1016/S0006-291X(02)00623-X. PMID 12083769.
• Liu Y, Sun W, Zhang K, Zheng H, Ma Y, Lin D, Zhang X, Feng L, Lei W, Zhang Z, Guo S, Han N, Tong W, Feng X, Gao Y, Cheng S (Jun 2007). "Identification of genes differentially expressed in human primary lung squamous cell carcinoma". Lung Cancer. 56 (3): 307–17. doi:10.1016/j.lungcan.2007.01.016. PMID 17316888.
• Suzuki Y, Yoshitomo-Nakagawa K, Maruyama K, Suyama A, Sugano S (Oct 1997). "Construction and characterization of a full length-enriched and a 5'-end-enriched cDNA library". Gene. 200 (1–2): 149–56. doi:10.1016/S0378-1119(97)00411-3. PMID 9373149.
• Lu Y, Dollé ME, Imholz S, van 't Slot R, Verschuren WM, Wijmenga C, Feskens EJ, Boer JM (Dec 2008). "Multiple genetic variants along candidate pathways influence plasma high-density lipoprotein cholesterol concentrations". Journal of Lipid Research. 49 (12): 2582–9. doi:10.1194/jlr.M800232-JLR200. PMID 18660489.
• Mehrle A, Rosenfelder H, Schupp I, del Val C, Arlt D, Hahne F, Bechtel S, Simpson J, Hofmann O, Hide W, Glatting KH, Huber W, Pepperkok R, Poustka A, Wiemann S (Jan 2006). "The LIFEdb database in 2006". Nucleic Acids Research. 34 (Database issue): D415–8. doi:10.1093/nar/gkj139. PMC 1347501. PMID 16381901.
• Hartley JL, Temple GF, Brasch MA (Nov 2000). "DNA cloning using in vitro site-specific recombination". Genome Research. 10 (11): 1788–95. doi:10.1101/gr.143000. PMC 310948. PMID 11076863.
• Maruyama K, Sugano S (Jan 1994). "Oligo-capping: a simple method to replace the cap structure of eukaryotic mRNAs with oligoribonucleotides". Gene. 138 (1–2): 171–4. doi:10.1016/0378-1119(94)90802-8. PMID 8125298.
• Nakamura Y, Sakakibara J, Izumi T, Shibata A, Ono T (Apr 1996). "Transcriptional regulation of squalene epoxidase by sterols and inhibitors in HeLa cells". The Journal of Biological Chemistry. 271 (14): 8053–6. doi:10.1074/jbc.271.14.8053. PMID 8626488.
• Nagai M, Sakakibara J, Wakui K, Fukushima Y, Igarashi S, Tsuji S, Arakawa M, Ono T (Aug 1997). "Localization of the squalene epoxidase gene (SQLE) to human chromosome region 8q24.1". Genomics. 44 (1): 141–3. doi:10.1006/geno.1997.4825. PMID 9286711.
• Wiemann S, Arlt D, Huber W, Wellenreuther R, Schleeger S, Mehrle A, Bechtel S, Sauermann M, Korf U, Pepperkok R, Sültmann H, Poustka A (Oct 2004). "From ORFeome to biology: a functional genomics pipeline". Genome Research. 14 (10B): 2136–44. doi:10.1101/gr.2576704. PMC 528930. PMID 15489336.

External links

• Squalene+monooxygenase at the US National Library of Medicine Medical Subject Headings (MeSH)

This article incorporates text from the United States National Library of Medicine, which is in the public domain.