Lanosterol synthase

Last updated
lanosterol synthase
Identifiers
EC no. 5.4.99.7
CAS no. 9032-71-7
Databases
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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
LSS
PDB 1w6j EBI.jpg
Available structures
PDB Ortholog search: PDBe RCSB
Identifiers
Aliases LSS , OSC, CTRCT44, lanosterol synthase (2,3-oxidosqualene-lanosterol cyclase), lanosterol synthase, HYPT14, APMR4
External IDs OMIM: 600909 MGI: 1336155 HomoloGene: 37408 GeneCards: LSS
Orthologs
SpeciesHumanMouse
Entrez

4047

16987

Ensembl

ENSG00000160285
ENSG00000281289

ENSMUSG00000033105

UniProt

P48449

Q8BLN5

RefSeq (mRNA)

NM_001001438
NM_001145436
NM_001145437
NM_002340

NM_146006

RefSeq (protein)

NP_001001438
NP_001138908
NP_001138909
NP_002331

NP_666118

Location (UCSC) Chr 21: 46.19 – 46.23 Mb Chr 10: 76.37 – 76.39 Mb
PubMed search [3] [4]
Wikidata
View/Edit Human View/Edit Mouse

Lanosterol synthase (EC 5.4.99.7) is an oxidosqualene cyclase (OSC) enzyme that converts (S)-2,3-oxidosqualene to a protosterol cation and finally to lanosterol. [5] Lanosterol is a key four-ringed intermediate in cholesterol biosynthesis. [6] [7] In humans, lanosterol synthase is encoded by the LSS gene. [8] [9]

Contents

In eukaryotes, lanosterol synthase is an integral monotopic protein associated with the cytosolic side of the endoplasmic reticulum. [10] Some evidence suggests that the enzyme is a soluble, non-membrane bound protein in the few prokaryotes that produce it. [11]

Due to the enzyme's role in cholesterol biosynthesis, there is interest in lanosterol synthase inhibitors as potential cholesterol-reducing drugs, to complement existing statins. [12]

Mechanism

Figure 1: Lanosterol synthase mechanism. The discrete carbocation intermediates show the non-concerted nature of the mechanism. Lanosterol Synthase Mech.tif
Figure 1: Lanosterol synthase mechanism. The discrete carbocation intermediates show the non-concerted nature of the mechanism.

Though some data on the mechanism has been obtained by the use of suicide inhibitors, mutagenesis studies, and homology modeling, it is still not fully understood how the enzyme catalyzes the formation of lanosterol. [12]

Initial epoxide protonation and ring opening

Before the acquisition of the protein's X-ray crystal structure, site-directed mutagenesis was used to determine residues key to the enzyme's catalytic activity. It was determined that an aspartic acid residue (D455) and two histidine residues (H146 and H234) were essential to enzyme function. Corey et al. hypothesized that the aspartic acid acts by protonating the substrate's epoxide ring, thus increasing its susceptibility to intramolecular attack by the nearest double bond, with H146 possibly intensifying the proton donor ability of the aspartic acid through hydrogen bonding. [13] After acquisition of the X-ray crystal structure of the enzyme, the role of D455 as a proton donor to the substrate's epoxide was confirmed, though it was found that D455 is more likely stabilized by hydrogen bonding from two cysteine residues (C456 and C533) than from the earlier suggested histidine. [12]

Ring formation cascade

Epoxide protonation activates the substrate, setting off a cascade of ring forming reactions. Four rings in total (A through D) are formed, producing the cholesterol backbone. [12] Though the idea of a concerted formation of all four rings had been entertained in the past, kinetic studies with (S)-2,3-oxidosqualene analogs showed that product formation is achieved through discrete carbocation intermediates (see Figure 1). Isolation of monocyclic and bicyclic products from lanosterol synthase mutants has further weakened the hypothesis of a concerted mechanism. [14] [15] Evidence suggests that epoxide ring opening and A ring formation is concerted, though. [16]

Structure

Lanosterol synthase is a two-domain monomeric protein [10] composed of two connected (α/α) barrel domains and three smaller β-structures. The enzyme active site is in the center of the protein, closed off by a constricted channel. Passage of the (S)-2,3-epoxysqualene substrate through the channel requires a change in protein conformation. In eukaryotes, a hydrophobic surface (6% of the total enzyme surface area) is the ER membrane-binding region (see Figure 2). [12]

The enzyme contains five fingerprint regions containing Gln-Trp motifs, which are also present in the highly analogous bacterial enzyme squalene-hopene cyclase. [12] Residues of these fingerprint regions contain stacked sidechains which are thought to contribute to enzyme stability during the highly exergonic cyclization reactions catalyzed by the enzyme. [17]

Function

Catalysis of lanosterol formation

Lanosterol synthase catalyzes the conversion of (S)-2,3-epoxysqualene to lanosterol, a key four-ringed intermediate in cholesterol biosynthesis. [6] [7] Thus, it in turn provides the precursor to estrogens, androgens, progestogens, glucocorticoids, mineralocorticoids, and neurosteroids. In eukaryotes the enzyme is bound to the cytosolic side of the endoplasmic reticulum membrane. [10] While cholesterol synthesis is mostly associated with eukaryotes, few prokaryotes have been found to express lanosterol synthase; it has been found as a soluble protein in Methylococcus capsulatus . [11]

Catalysis of epoxylanosterol formation

Lanosterol synthase also catalyzes the cyclization of 2,3;22,23-diepoxysqualene to 24(S),25-epoxylanosterol, [18] which is later converted to 24(S),25-epoxycholesterol. [19] Since the enzyme affinity for this second substrate is greater than for the monoepoxy (S)-2,3-epoxysqualene, under partial inhibition conversion of 2,3;22,23-diepoxysqualene to 24(S),25-epoxylanosterol is favored over lanosterol synthesis. [20] This has relevance for disease prevention and treatment.

Clinical significance

Enzyme inhibitors as cholesterol-lowering drugs

Interest has grown in lanosterol synthase inhibitors as drugs to lower blood cholesterol and treat atherosclerosis. The widely popular statin drugs currently used to lower LDL (low-density lipoprotein) cholesterol function by inhibiting HMG-CoA reductase activity. [6] Because this enzyme catalyzes the formation of precursors far upstream of (S)-2,3-epoxysqualene and cholesterol, statins may negatively influence amounts of intermediates required for other biosynthetic pathways (e.g. synthesis of isoprenoids, coenzyme Q). Thus, lanosterol synthase, which is more closely tied to cholesterol biosynthesis than HMG-CoA reductase, is an attractive drug target. [21]

Lanosterol synthase inhibitors are thought to lower LDL and VLDL cholesterol by a dual control mechanism. Studies in which lanosterol synthase is partially inhibited have shown both a direct decrease in lanosterol formation and a decrease in HMG-CoA reductase activity. The oxysterol 24(S),25-epoxylanosterol, which is preferentially formed over lanosterol during partial lanosterol synthase inhibition, is believed to be responsible for this inhibition of HMG-CoA reductase activity. [22]

Evolution

It is believed that oxidosqualene cyclases (OSCs, the class to which lanosterol cyclase belongs) evolved from bacterial squalene-hopene cyclase (SHC), which is involved with the formation of hopanoids. Phylogenetic trees constructed from the amino acid sequences of OSCs in diverse organisms suggest a single common ancestor, and that the synthesis pathway evolved only once. [23] The discovery of steranes including cholestane in 2.7-billion year-old shales from Pilbara Craton, Australia, suggests that eukaryotes with OSCs and complex steroid machinery were present early in earth's history. [24]

Related Research Articles

<span class="mw-page-title-main">Steroid</span> Polycyclic organic compound having sterane as a core structure

A steroid is an organic compound with four fused rings arranged in a specific molecular configuration.

<span class="mw-page-title-main">Squalene</span> Chemical compound

Squalene is an organic compound. It is a triterpene with the formula C30H50. It is a colourless oil, although impure samples appear yellow. It was originally obtained from shark liver oil (hence its name, as Squalus is a genus of sharks). An estimated 12% of bodily squalene in humans is found in sebum. Squalene has a role in topical skin lubrication and protection.

<span class="mw-page-title-main">Hopanoids</span> Class of chemical compounds

Hopanoids are a diverse subclass of triterpenoids with the same hydrocarbon skeleton as the compound hopane. This group of pentacyclic molecules therefore refers to simple hopenes, hopanols and hopanes, but also to extensively functionalized derivatives such as bacteriohopanepolyols (BHPs) and hopanoids covalently attached to lipid A.

<span class="mw-page-title-main">Lanosterol</span> Chemical compound

Lanosterol is a tetracyclic triterpenoid and is the compound from which all animal and fungal steroids are derived. By contrast, plant steroids are produced via cycloartenol.

<span class="mw-page-title-main">Farnesyl-diphosphate farnesyltransferase</span> Class of enzymes

Squalene synthase (SQS) or farnesyl-diphosphate:farnesyl-diphosphate farnesyl transferase is an enzyme localized to the membrane of the endoplasmic reticulum. SQS participates in the isoprenoid biosynthetic pathway, catalyzing a two-step reaction in which two identical molecules of farnesyl pyrophosphate (FPP) are converted into squalene, with the consumption of NADPH. Catalysis by SQS is the first committed step in sterol synthesis, since the squalene produced is converted exclusively into various sterols, such as cholesterol, via a complex, multi-step pathway. SQS belongs to squalene/phytoene synthase family of proteins.

(S)-2,3-Oxidosqualene ((S)-2,3-epoxysqualene) is an intermediate in the synthesis of the cell membrane sterol precursors lanosterol and cycloartenol, as well as saponins. It is formed when squalene is oxidized by the enzyme squalene monooxygenase. 2,3-Oxidosqualene is the substrate of various oxidosqualene cyclases, including lanosterol synthase, which produces lanosterol, a precursor to cholesterol.

<span class="mw-page-title-main">Squalene monooxygenase</span> Mammalian protein found in Homo sapiens

Squalene monooxygenase is a eukaryotic enzyme that uses NADPH and diatomic oxygen to oxidize squalene to 2,3-oxidosqualene. 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 genomes lack a squalene monooxygenase encoding gene, but instead encode an alternative squalene epoxidase that performs the same task.

<span class="mw-page-title-main">Lanosterol 14 alpha-demethylase</span> Protein-coding gene in the species Homo sapiens

Lanosterol 14α-demethylase (CYP51A1) is the animal version of a cytochrome P450 enzyme that is involved in the conversion of lanosterol to 4,4-dimethylcholesta-8(9),14,24-trien-3β-ol. The cytochrome P450 isoenzymes are a conserved group of proteins that serve as key players in the metabolism of organic substances and the biosynthesis of important steroids, lipids, and vitamins in eukaryotes. As a member of this family, lanosterol 14α-demethylase is responsible for an essential step in the biosynthesis of sterols. In particular, this protein catalyzes the removal of the C-14α-methyl group from lanosterol. This demethylation step is regarded as the initial checkpoint in the transformation of lanosterol to other sterols that are widely used within the cell.

Purine metabolism refers to the metabolic pathways to synthesize and break down purines that are present in many organisms.

<span class="mw-page-title-main">Prenyltransferase</span>

Prenyltransferases (PTs) are a class of enzymes that transfer allylic prenyl groups to acceptor molecules. Prenyl transferases commonly refer to isoprenyl diphosphate syntheses (IPPSs). Prenyltransferases are a functional category and include several enzyme groups that are evolutionarily independent.

<span class="mw-page-title-main">Sterol 14-demethylase</span> Class of enzymes

In enzymology, a sterol 14-demethylase (EC 1.14.13.70) is an enzyme of the cytochrome P450 (CYP) superfamily. It is any member of the CYP51 family. It catalyzes a chemical reaction such as:

In enzymology, a cycloartenol synthase (EC 5.4.99.8) is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Hydroxymethylglutaryl-CoA synthase</span> Class of enzymes

In molecular biology, hydroxymethylglutaryl-CoA synthase or HMG-CoA synthase EC 2.3.3.10 is an enzyme which catalyzes the reaction in which acetyl-CoA condenses with acetoacetyl-CoA to form 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA). This reaction comprises the second step in the mevalonate-dependent isoprenoid biosynthesis pathway. HMG-CoA is an intermediate in both cholesterol synthesis and ketogenesis. This reaction is overactivated in patients with diabetes mellitus type 1 if left untreated, due to prolonged insulin deficiency and the exhaustion of substrates for gluconeogenesis and the TCA cycle, notably oxaloacetate. This results in shunting of excess acetyl-CoA into the ketone synthesis pathway via HMG-CoA, leading to the development of diabetic ketoacidosis.

In enzymology, a geranyltranstransferase is an enzyme that catalyzes the chemical reaction

<span class="mw-page-title-main">Zaragozic acid</span> Chemical compound

Zaragozic acids are a family of natural products produced by fungi. The first characterized zaragozic acids, A, B, and C were isolated from an unidentified sterile fungal culture, Sporormiella intermedia, and L. elatius, respectively. just outside the European city Zaragoza, Spain on the Jalón river. This family of natural products possesses a unique 4,8-dioxabicyclo[3.2.1]octane core, and vary in their 1-alkyl and their 6-acyl side chains.

<span class="mw-page-title-main">Squalene-hopene cyclase</span>

Squalene-hopene cyclase (SHC) (EC 5.4.99.17) or hopan-22-ol hydro-lyase is an enzyme in the terpene cyclase/mutase family. It catalyzes the interconversion of squalene into a pentacyclic triterpenes, hopene and hopanol. This enzyme catalyses the following chemical reactions.

β-amyrin synthase is an enzyme with systematic name (3S)-2,3-epoxy-2,3-dihydrosqualene mutase . This enzyme catalyses the following chemical reaction

<span class="mw-page-title-main">C-5 sterol desaturase</span> Class of enzymes

C-5 sterol desaturase is an enzyme that is highly conserved among eukaryotes and catalyzes the dehydrogenation of a C-5(6) bond in a sterol intermediate compound as a step in the biosynthesis of major sterols. The precise structure of the enzyme's substrate varies by species. For example, the human C-5 sterol desaturase oxidizes lathosterol, while its ortholog ERG3 in the yeast Saccharomyces cerevisiae oxidizes episterol.

<span class="mw-page-title-main">Oxidosqualene cyclase</span>

Oxidosqualene cyclases (OSC) are enzymes involved in cyclization reactions of 2,3-oxidosqualene to form sterols or triterpenes.

Pierre Benveniste, born on 22 December 1937 in Neuilly-sur-Seine, is a French researcher in plant biochemistry and professor at the University of Strasbourg.

References

  1. 1 2 3 ENSG00000281289 GRCh38: Ensembl release 89: ENSG00000160285, ENSG00000281289 - Ensembl, May 2017
  2. 1 2 3 GRCm38: Ensembl release 89: ENSMUSG00000033105 - Ensembl, May 2017
  3. ↑ "Human PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  4. ↑ "Mouse PubMed Reference:". National Center for Biotechnology Information, U.S. National Library of Medicine.
  5. ↑ Dean PD, Ortiz de Montellano PR, Bloch K, Corey EJ (Jun 1967). "A soluble 2,3-oxidosqualene sterol cyclase". The Journal of Biological Chemistry. 242 (12): 3014–5. doi: 10.1016/S0021-9258(18)99606-7 . PMID   6027261.
  6. 1 2 3 Huff MW, Telford DE (Jul 2005). "Lord of the rings--the mechanism for oxidosqualene:lanosterol cyclase becomes crystal clear". Trends in Pharmacological Sciences. 26 (7): 335–340. doi:10.1016/j.tips.2005.05.004. PMID   15951028.
  7. 1 2 Yamamoto S, Lin K, Bloch K (May 1969). "Some properties of the microsomal 2,3-oxidosqualene sterol cyclase". Proceedings of the National Academy of Sciences of the United States of America. 63 (1): 110–7. Bibcode:1969PNAS...63..110Y. doi: 10.1073/pnas.63.1.110 . PMC   534008 . PMID   5257956.
  8. ↑ Baker CH, Matsuda SP, Liu DR, Corey EJ (Aug 1995). "Molecular cloning of the human gene encoding lanosterol synthase from a liver cDNA library". Biochemical and Biophysical Research Communications. 213 (1): 154–160. doi:10.1006/bbrc.1995.2110. PMID   7639730.
  9. ↑ Young M, Chen H, Lalioti MD, Antonarakis SE (May 1996). "The human lanosterol synthase gene maps to chromosome 21q22.3". Human Genetics. 97 (5): 620–624. doi:10.1007/BF02281872. PMID   8655142. S2CID   21051816.
  10. 1 2 3 Ruf A, Müller F, D'Arcy B, Stihle M, Kusznir E, Handschin C, Morand OH, Thoma R (Mar 2004). "The monotopic membrane protein human oxidosqualene cyclase is active as monomer". Biochemical and Biophysical Research Communications. 315 (2): 247–254. doi:10.1016/j.bbrc.2004.01.052. PMID   14766201.
  11. 1 2 Lamb DC, Jackson CJ, Warrilow AG, Manning NJ, Kelly DE, Kelly SL (Aug 2007). "Lanosterol biosynthesis in the prokaryote Methylococcus capsulatus: insight into the evolution of sterol biosynthesis". Molecular Biology and Evolution. 24 (8): 1714–1721. doi: 10.1093/molbev/msm090 . PMID   17567593.
  12. 1 2 3 4 5 6 Thoma R, Schulz-Gasch T, D'Arcy B, Benz J, Aebi J, Dehmlow H, Hennig M, Stihle M, Ruf A (Nov 2004). "Insight into steroid scaffold formation from the structure of human oxidosqualene cyclase". Nature. 432 (7013): 118–122. Bibcode:2004Natur.432..118T. doi:10.1038/nature02993. PMID   15525992. S2CID   364281.
  13. ↑ Corey EJ, Cheng CH, Baker CH, Matsuda SP, Li D, Song X (February 1997). "Studies on the Substrate Binding Segments and Catalytic Action of Lanosterol Synthase. Affinity Labeling with Carbocations Derived from Mechanism-Based Analogs of 2, 3-Oxidosqualene and Site-Directed Mutagenesis Probes". J. Am. Chem. Soc. 119 (6): 1289–96. doi:10.1021/ja963228o.
  14. ↑ Wu TK, Wang TT, Chang CH, Liu YT, Shie WS (Nov 2008). "Importance of Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase tyrosine 707 residue for chair-boat bicyclic ring formation and deprotonation reactions". Organic Letters. 10 (21): 4959–62. doi:10.1021/ol802036c. PMID   18842050.
  15. ↑ Joubert BM, Hua L, Matsuda SP (Feb 2000). "Steric bulk at position 454 in Saccharomyces cerevisiae lanosterol synthase influences B-ring formation but not deprotonation". Organic Letters. 2 (3): 339–41. doi:10.1021/ol9912940. PMID   10814317.
  16. ↑ Corey EJ, Cheng CH, Baker CH, Matsuda SP, Li D, Song X (February 1997). "Methodology for the Preparation of Pure Recombinant S. cerevisiae Lanosterol Synthase Using a Baculovirus Expression System. Evidence That Oxirane Cleavage and A-Ring Formation Are Concerted in the Biosynthesis of Lanosterol from 2,3-Oxidosqualene". J. Am. Chem. Soc. 119 (6): 1277–88. doi:10.1021/ja963227w.
  17. ↑ Wendt KU, Poralla K, Schulz GE (Sep 1997). "Structure and function of a squalene cyclase". Science. 277 (5333): 1811–15. doi:10.1126/science.277.5333.1811. PMID   9295270.
  18. ↑ Corey EJ, Gross SK (Aug 1967). "Formation of sterols by the action of 2,3-oxidosqualene-sterol cyclase on the factitious substrates 2,3:22,23-dioxidosqualene and 2,3-oxido-22,23-dihydrosqualene". Journal of the American Chemical Society. 89 (17): 4561–2. doi:10.1021/ja00993a079. PMID   6046552.
  19. ↑ Nelson JA, Steckbeck SR, Spencer TA (Feb 1981). "Biosynthesis of 24,25-epoxycholesterol from squalene 2,3;22,23-dioxide". The Journal of Biological Chemistry. 256 (3): 1067–8. doi: 10.1016/S0021-9258(19)69921-7 . PMID   7451488.
  20. ↑ Boutaud O, Dolis D, Schuber F (Oct 1992). "Preferential cyclization of 2,3(S):22(S),23-dioxidosqualene by mammalian 2,3-oxidosqualene-lanosterol cyclase". Biochemical and Biophysical Research Communications. 188 (2): 898–904. doi:10.1016/0006-291X(92)91140-L. PMID   1445330.
  21. ↑ Telford DE, Lipson SM, Barrett PH, Sutherland BG, Edwards JY, Aebi JD, Dehmlow H, Morand OH, Huff MW (Dec 2005). "A novel inhibitor of oxidosqualene:lanosterol cyclase inhibits very low-density lipoprotein apolipoprotein B100 (apoB100) production and enhances low-density lipoprotein apoB100 catabolism through marked reduction in hepatic cholesterol content". Arteriosclerosis, Thrombosis, and Vascular Biology. 25 (12): 2608–14. doi: 10.1161/01.ATV.0000189158.28455.94 . PMID   16210564.
  22. ↑ Panini SR, Gupta A, Sexton RC, Parish EJ, Rudney H (Oct 1987). "Regulation of sterol biosynthesis and of 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity in cultured cells by progesterone". The Journal of Biological Chemistry. 262 (30): 14435–40. doi: 10.1016/S0021-9258(18)47813-1 . PMID   3667583.
  23. ↑ Pearson A, Budin M, Brocks JJ (Dec 2003). "Phylogenetic and biochemical evidence for sterol synthesis in the bacterium Gemmata obscuriglobus". Proceedings of the National Academy of Sciences of the United States of America. 100 (26): 15352–7. Bibcode:2003PNAS..10015352P. doi: 10.1073/pnas.2536559100 . PMC   307571 . PMID   14660793.
  24. ↑ Brocks JJ, Logan GA, Buick R, Summons RE (Aug 1999). "Archean molecular fossils and the early rise of eukaryotes". Science. 285 (5430): 1033–6. Bibcode:1999Sci...285.1033B. CiteSeerX   10.1.1.516.9123 . doi:10.1126/science.285.5430.1033. PMID   10446042.

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