The Enzyme Database

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EC 1.3.1.96     
Accepted name: Botryococcus squalene synthase
Reaction: squalene + diphosphate + NADP+ = presqualene diphosphate + NADPH + H+
For diagram of botryococcus braunii BOT22 squalene and botrycoccene biosynthesis, click here
Other name(s): SSL-2 (gene name)
Systematic name: squalene:NADP+ oxidoreductase
Comments: Isolated from the green alga Botryococcus braunii BOT22. Acts in the reverse direction. cf. EC 2.5.1.21, squalene synthase, where squalene is formed directly from farnesyl diphosphate.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Niehaus, T.D., Okada, S., Devarenne, T.P., Watt, D.S., Sviripa, V. and Chappell, J. Identification of unique mechanisms for triterpene biosynthesis in Botryococcus braunii. Proc. Natl. Acad. Sci. USA 108 (2011) 12260–12265. [DOI] [PMID: 21746901]
[EC 1.3.1.96 created 2012]
 
 
EC 1.3.1.97     
Accepted name: botryococcene synthase
Reaction: C30 botryococcene + NADP+ + diphosphate = presqualene diphosphate + NADPH + H+
For diagram of botryococcus braunii BOT22 squalene and botrycoccene biosynthesis, click here
Glossary: C30 botryococcene = (10S,13R)-10-ethenyl-2,6,10,13,17,21-hexamethyldocosa-2,5,11,16,20-pentaene
Other name(s): SSL-3 (gene name)
Systematic name: C30 botryococcene:NADP+ oxidoreductase
Comments: Isolated from the green alga Botryococcus braunii BOT22. Acts in the reverse direction. Involved in the production of botryococcenes, which are triterpenoid hydrocarbons of isoprenoid origin produced in large amount by this alga.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Niehaus, T.D., Okada, S., Devarenne, T.P., Watt, D.S., Sviripa, V. and Chappell, J. Identification of unique mechanisms for triterpene biosynthesis in Botryococcus braunii. Proc. Natl. Acad. Sci. USA 108 (2011) 12260–12265. [DOI] [PMID: 21746901]
[EC 1.3.1.97 created 2012]
 
 
EC 1.17.8.1     
Accepted name: hydroxysqualene dehydroxylase
Reaction: squalene + FAD + H2O = hydroxysqualene + FADH2
Glossary: hydroxysqualene = (6E,10E,12R,14E,18E)-2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaen-12-ol
Other name(s): hpnE (gene name)
Systematic name: squalene:FAD oxidoreductase (hydroxylating)
Comments: This enzyme, isolated from the bacteria Rhodopseudomonas palustris and Zymomonas mobilis, participates, along with EC 2.5.1.103, presqualene diphosphate synthase, and EC 4.2.3.156, hydroxysqualene synthase, in the conversion of all-trans-farnesyl diphosphate to squalene. Eukaryotes achieve the same goal in a single step, catalysed by EC 2.5.1.21, squalene synthase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Pan, J.J., Solbiati, J.O., Ramamoorthy, G., Hillerich, B.S., Seidel, R.D., Cronan, J.E., Almo, S.C. and Poulter, C.D. Biosynthesis of squalene from farnesyl diphosphate in bacteria: three steps catalyzed by three enzymes. ACS Cent. Sci. 1 (2015) 77–82. [DOI] [PMID: 26258173]
[EC 1.17.8.1 created 2016]
 
 
EC 2.5.1.21     
Accepted name: squalene synthase
Reaction: 2 (2E,6E)-farnesyl diphosphate + NAD(P)H + H+ = squalene + 2 diphosphate + NAD(P)+ (overall reaction)
(1a) 2 (2E,6E)-farnesyl diphosphate = diphosphate + presqualene diphosphate
(1b) presqualene diphosphate + NAD(P)H + H+ = squalene + diphosphate + NAD(P)+
For diagram of squalene, phytoene and 4,4′-diapophytoene biosynthesis, click here
Other name(s): farnesyltransferase; presqualene-diphosphate synthase; presqualene synthase; squalene synthetase; farnesyl-diphosphate farnesyltransferase; SQS
Systematic name: (2E,6E)-farnesyl-diphosphate:(2E,6E)-farnesyl-diphosphate farnesyltransferase
Comments: This microsomal enzyme catalyses the first committed step in the biosynthesis of sterols. The enzyme from yeast requires either Mg2+ or Mn2+ for activity. In the absence of NAD(P)H, presqualene diphosphate (PSPP) is accumulated. When NAD(P)H is present, presqualene diphosphate does not dissociate from the enzyme during the synthesis of squalene from farnesyl diphosphate (FPP) [8]. High concentrations of FPP inhibit the production of squalene but not of PSPP [8].
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, PDB, CAS registry number: 9077-14-9
References:
1.  Kuswick-Rabiega, G. and Rilling, H.C. Squalene synthetase. Solubilization and partial purification of squalene synthetase, copurification of presqualene pyrophosphate and squalene synthetase activities. J. Biol. Chem. 262 (1987) 1505–1509. [PMID: 3805037]
2.  Ericsson, J., Appelkvist, E.L., Thelin, A., Chojnacki, T. and Dallner, G. Isoprenoid biosynthesis in rat liver peroxisomes. Characterization of cis-prenyltransferase and squalene synthetase. J. Biol. Chem. 267 (1992) 18708–18714. [PMID: 1527001]
3.  Tansey, T.R. and Shechter, I. Structure and regulation of mammalian squalene synthase. Biochim. Biophys. Acta 1529 (2000) 49–62. [DOI] [PMID: 11111077]
4.  LoGrasso, P.V., Soltis, D.A. and Boettcher, B.R. Overexpression, purification, and kinetic characterization of a carboxyl-terminal-truncated yeast squalene synthetase. Arch. Biochem. Biophys. 307 (1993) 193–199. [DOI] [PMID: 8239656]
5.  Shechter, I., Klinger, E., Rucker, M.L., Engstrom, R.G., Spirito, J.A., Islam, M.A., Boettcher, B.R. and Weinstein, D.B. Solubilization, purification, and characterization of a truncated form of rat hepatic squalene synthetase. J. Biol. Chem. 267 (1992) 8628–8635. [PMID: 1569107]
6.  Agnew, W.S. and Popják, G. Squalene synthetase. Stoichiometry and kinetics of presqualene pyrophosphate and squalene synthesis by yeast microsomes. J. Biol. Chem. 253 (1978) 4566–4573. [PMID: 26684]
7.  Pandit, J., Danley, D.E., Schulte, G.K., Mazzalupo, S., Pauly, T.A., Hayward, C.M., Hamanaka, E.S., Thompson, J.F. and Harwood, H.J., Jr. Crystal structure of human squalene synthase. A key enzyme in cholesterol biosynthesis. J. Biol. Chem. 275 (2000) 30610–30617. [DOI] [PMID: 10896663]
8.  Radisky, E.S. and Poulter, C.D. Squalene synthase: steady-state, pre-steady-state, and isotope-trapping studies. Biochemistry 39 (2000) 1748–1760. [DOI] [PMID: 10677224]
[EC 2.5.1.21 created 1976, modified 2005, modified 2012]
 
 
EC 2.5.1.96     
Accepted name: 4,4′-diapophytoene synthase
Reaction: 2 (2E,6E)-farnesyl diphosphate = 15-cis-4,4′-diapophytoene + 2 diphosphate (overall reaction)
(1a) 2 (2E,6E)-farnesyl diphosphate = diphosphate + presqualene diphosphate
(1b) presqualene diphosphate = 15-cis-4,4′-diapophytoene + diphosphate
For diagram of squalene, phytoene and 4,4′-diapophytoene biosynthesis, click here
Other name(s): dehydrosqualene synthase; DAP synthase; C30 carotene synthase; CrtM
Systematic name: farnesyl-diphosphate:farnesyl-diphosphate farnesyltransferase (15-cis-4,4′-diapophytoene forming)
Comments: Requires Mn2+. Typical of Staphylococcus aureus and some other bacteria such as Heliobacillus sp.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Umeno, D., Tobias, A.V. and Arnold, F.H. Evolution of the C30 carotenoid synthase CrtM for function in a C40 pathway. J. Bacteriol. 184 (2002) 6690–6699. [DOI] [PMID: 12426357]
2.  Pelz, A., Wieland, K.P., Putzbach, K., Hentschel, P., Albert, K. and Gotz, F. Structure and biosynthesis of staphyloxanthin from Staphylococcus aureus. J. Biol. Chem. 280 (2005) 32493–32498. [DOI] [PMID: 16020541]
3.  Ku, B., Jeong, J.C., Mijts, B.N., Schmidt-Dannert, C. and Dordick, J.S. Preparation, characterization, and optimization of an in vitro C30 carotenoid pathway. Appl. Environ. Microbiol. 71 (2005) 6578–6583. [DOI] [PMID: 16269684]
4.  Liu, C.I., Liu, G.Y., Song, Y., Yin, F., Hensler, M.E., Jeng, W.Y., Nizet, V., Wang, A.H. and Oldfield, E. A cholesterol biosynthesis inhibitor blocks Staphylococcus aureus virulence. Science 319 (2008) 1391–1394. [DOI] [PMID: 18276850]
[EC 2.5.1.96 created 2011]
 
 
EC 2.5.1.103     
Accepted name: presqualene diphosphate synthase
Reaction: 2 (2E,6E)-farnesyl diphosphate = presqualene diphosphate + diphosphate
For diagram of botryococcus braunii BOT22 squalene and botrycoccene biosynthesis, click here
Other name(s): SSL-1 (gene name); hpnD (gene name)
Systematic name: (2E,6E)-farnesyl-diphosphate:(2E,6E)-farnesyl-diphosphate farnesyltransferase (presqualene diphosphate-forming)
Comments: Isolated from the green alga Botryococcus braunii BOT22. Unlike EC 2.5.1.21, squalene synthase, where squalene is formed in one step from farnesyl diphosphate, in this alga the intermediate presqualene diphosphate is generated and released by this enzyme. This compound is then converted into either squalene (by EC 1.3.1.96, Botryococcus squalene synthase) or botryococcene (EC 1.3.1.97, botryococcene synthase).
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Niehaus, T.D., Okada, S., Devarenne, T.P., Watt, D.S., Sviripa, V. and Chappell, J. Identification of unique mechanisms for triterpene biosynthesis in Botryococcus braunii. Proc. Natl. Acad. Sci. USA 108 (2011) 12260–12265. [DOI] [PMID: 21746901]
2.  Pan, J.J., Solbiati, J.O., Ramamoorthy, G., Hillerich, B.S., Seidel, R.D., Cronan, J.E., Almo, S.C. and Poulter, C.D. Biosynthesis of squalene from farnesyl diphosphate in bacteria: three steps catalyzed by three enzymes. ACS Cent. Sci. 1 (2015) 77–82. [DOI] [PMID: 26258173]
[EC 2.5.1.103 created 2012]
 
 
EC 4.2.3.156     
Accepted name: hydroxysqualene synthase
Reaction: presqualene diphosphate + H2O = hydroxysqualene + diphosphate
For diagram of botryococcus braunii BOT22 squalene and botrycoccene biosynthesis, click here
Glossary: presqualene = {(1R,2R,3R)-2-[(3E)-4,8-dimethylnona-3,7-dien-1-yl]-2-methyl-3-[(2E,6E)-2,6,10-trimethylundeca-1,5,9-trien-1-yl]cyclopropan-1-yl}methyl
hydroxysqualene = (6E,10E,12R,14E,18E)-2,6,10,15,19,23-hexamethyltetracosa-2,6,10,14,18,22-hexaen-12-ol
Other name(s): hpnC (gene name)
Systematic name: presqualene diphosphate diphosphate-lyase (adding water; hydroxyasqualene-forming)
Comments: This enzyme, isolated from the bacteria Rhodopseudomonas palustris and Zymomonas mobilis, participates, along with EC 2.5.1.103, presqualene diphosphate synthase, and EC 1.17.8.1, hydroxysqualene dehydroxylase, in the conversion of all-trans-farnesyl diphosphate to squalene. Eukaryotes achieve the same goal in a single step, catalysed by EC 2.5.1.21, squalene synthase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Pan, J.J., Solbiati, J.O., Ramamoorthy, G., Hillerich, B.S., Seidel, R.D., Cronan, J.E., Almo, S.C. and Poulter, C.D. Biosynthesis of squalene from farnesyl diphosphate in bacteria: three steps catalyzed by three enzymes. ACS Cent. Sci. 1 (2015) 77–82. [DOI] [PMID: 26258173]
[EC 4.2.3.156 created 2016]
 
 


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