The Delta6 Fatty Acid Desaturase (Delta6-FADS)-like CD includes the integral-membrane enzymes: ...
218-469
8.08e-70
The Delta6 Fatty Acid Desaturase (Delta6-FADS)-like CD includes the integral-membrane enzymes: delta-4, delta-5, delta-6, delta-8, delta-8-sphingolipid, and delta-11 desaturases found in vertebrates, higher plants, fungi, and bacteria. These desaturases are required for the synthesis of highly unsaturated fatty acids (HUFAs), which are mainly esterified into phospholipids and contribute to maintaining membrane fluidity. While HUFAs may be required for cold tolerance in bacteria, plants and fish, the primary role of HUFAs in mammals is cell signaling. These enzymes are described as front-end desaturases because they introduce a double bond between the pre-exiting double bond and the carboxyl (front) end of the fatty acid. Various substrates are involved, with both acyl-coenzyme A (CoA) and acyl-lipid desaturases present in this CD. Acyl-lipid desaturases are localized in the membranes of cyanobacterial thylakoid, plant endoplasmic reticulum (ER), and plastid; and acyl-CoA desaturases are present in ER membrane. ER-bound plant acyl-lipid desaturases and acyl-CoA desaturases require cytochrome b5 as an electron donor. Most of the eukaryotic desaturase domains have an adjacent N-terminal cytochrome b5-like domain. This domain family has extensive hydrophobic regions that would be capable of spanning the membrane bilayer at least twice. Comparison of sequences also reveals the existence of three regions of conserved histidine cluster motifs that contain the residues: HXXXH, HXX(X)HH, and Q/HXXHH. These histidine residues are reported to be catalytically essential and proposed to be the ligands for the iron atoms contained within the homolog, stearoyl CoA desaturase.
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Pssm-ID: 239583 [Multi-domain] Cd Length: 204 Bit Score: 221.75 E-value: 8.08e-70
The Delta6 Fatty Acid Desaturase (Delta6-FADS)-like CD includes the integral-membrane enzymes: ...
218-469
8.08e-70
The Delta6 Fatty Acid Desaturase (Delta6-FADS)-like CD includes the integral-membrane enzymes: delta-4, delta-5, delta-6, delta-8, delta-8-sphingolipid, and delta-11 desaturases found in vertebrates, higher plants, fungi, and bacteria. These desaturases are required for the synthesis of highly unsaturated fatty acids (HUFAs), which are mainly esterified into phospholipids and contribute to maintaining membrane fluidity. While HUFAs may be required for cold tolerance in bacteria, plants and fish, the primary role of HUFAs in mammals is cell signaling. These enzymes are described as front-end desaturases because they introduce a double bond between the pre-exiting double bond and the carboxyl (front) end of the fatty acid. Various substrates are involved, with both acyl-coenzyme A (CoA) and acyl-lipid desaturases present in this CD. Acyl-lipid desaturases are localized in the membranes of cyanobacterial thylakoid, plant endoplasmic reticulum (ER), and plastid; and acyl-CoA desaturases are present in ER membrane. ER-bound plant acyl-lipid desaturases and acyl-CoA desaturases require cytochrome b5 as an electron donor. Most of the eukaryotic desaturase domains have an adjacent N-terminal cytochrome b5-like domain. This domain family has extensive hydrophobic regions that would be capable of spanning the membrane bilayer at least twice. Comparison of sequences also reveals the existence of three regions of conserved histidine cluster motifs that contain the residues: HXXXH, HXX(X)HH, and Q/HXXHH. These histidine residues are reported to be catalytically essential and proposed to be the ligands for the iron atoms contained within the homolog, stearoyl CoA desaturase.
Pssm-ID: 239583 [Multi-domain] Cd Length: 204 Bit Score: 221.75 E-value: 8.08e-70
Fatty acid desaturase; Fatty acid desaturases are enzymes that catalyze the insertion of a ...
213-475
4.67e-24
Fatty acid desaturase; Fatty acid desaturases are enzymes that catalyze the insertion of a double bond at the delta position of fatty acids. There seem to be two distinct families of fatty acid desaturases which do not seem to be evolutionary related: Family 1 composed of Stearoyl-CoA desaturases (SCD) and Family 2 composed of Bacterial fatty acid desaturases, Plant stearoyl-acyl-carrier-protein desaturase and Cyanobacterial DesA. Members of this entry are ER integral membrane proteins that share the same mushroom-shaped fold consisting of four transmembrane helices (TM1-TM4) which anchor them to the membrane, capped by a cytosolic domain containing a unique 9-10 histidine- coordinating di metal (di-iron) catalytic centre. The structure of mouse stearoyl-CoA desaturase (SDC) revealed that TM2 and TM4 are longer than TM1 and TM3 and protrude into the cytosolic domain, providing three of the nine histidine residues that coordinate the two metal ions, while the other histidine residues are provided by the soluble domain in this enzyme.
Pssm-ID: 425713 [Multi-domain] Cd Length: 252 Bit Score: 100.88 E-value: 4.67e-24
Cytochrome b5-like Heme/Steroid binding domain; This family includes heme binding domains from ...
78-150
3.76e-23
Cytochrome b5-like Heme/Steroid binding domain; This family includes heme binding domains from a diverse range of proteins. This family also includes proteins that bind to steroids. The family includes progesterone receptors. Many members of this subfamily are membrane anchored by an N-terminal transmembrane alpha helix. This family also includes a domain in some chitin synthases. There is no known ligand for this domain in the chitin synthases.
Pssm-ID: 459698 [Multi-domain] Cd Length: 74 Bit Score: 92.68 E-value: 3.76e-23
The Delta6 Fatty Acid Desaturase (Delta6-FADS)-like CD includes the integral-membrane enzymes: ...
218-469
8.08e-70
The Delta6 Fatty Acid Desaturase (Delta6-FADS)-like CD includes the integral-membrane enzymes: delta-4, delta-5, delta-6, delta-8, delta-8-sphingolipid, and delta-11 desaturases found in vertebrates, higher plants, fungi, and bacteria. These desaturases are required for the synthesis of highly unsaturated fatty acids (HUFAs), which are mainly esterified into phospholipids and contribute to maintaining membrane fluidity. While HUFAs may be required for cold tolerance in bacteria, plants and fish, the primary role of HUFAs in mammals is cell signaling. These enzymes are described as front-end desaturases because they introduce a double bond between the pre-exiting double bond and the carboxyl (front) end of the fatty acid. Various substrates are involved, with both acyl-coenzyme A (CoA) and acyl-lipid desaturases present in this CD. Acyl-lipid desaturases are localized in the membranes of cyanobacterial thylakoid, plant endoplasmic reticulum (ER), and plastid; and acyl-CoA desaturases are present in ER membrane. ER-bound plant acyl-lipid desaturases and acyl-CoA desaturases require cytochrome b5 as an electron donor. Most of the eukaryotic desaturase domains have an adjacent N-terminal cytochrome b5-like domain. This domain family has extensive hydrophobic regions that would be capable of spanning the membrane bilayer at least twice. Comparison of sequences also reveals the existence of three regions of conserved histidine cluster motifs that contain the residues: HXXXH, HXX(X)HH, and Q/HXXHH. These histidine residues are reported to be catalytically essential and proposed to be the ligands for the iron atoms contained within the homolog, stearoyl CoA desaturase.
Pssm-ID: 239583 [Multi-domain] Cd Length: 204 Bit Score: 221.75 E-value: 8.08e-70
Fatty acid desaturase; Fatty acid desaturases are enzymes that catalyze the insertion of a ...
213-475
4.67e-24
Fatty acid desaturase; Fatty acid desaturases are enzymes that catalyze the insertion of a double bond at the delta position of fatty acids. There seem to be two distinct families of fatty acid desaturases which do not seem to be evolutionary related: Family 1 composed of Stearoyl-CoA desaturases (SCD) and Family 2 composed of Bacterial fatty acid desaturases, Plant stearoyl-acyl-carrier-protein desaturase and Cyanobacterial DesA. Members of this entry are ER integral membrane proteins that share the same mushroom-shaped fold consisting of four transmembrane helices (TM1-TM4) which anchor them to the membrane, capped by a cytosolic domain containing a unique 9-10 histidine- coordinating di metal (di-iron) catalytic centre. The structure of mouse stearoyl-CoA desaturase (SDC) revealed that TM2 and TM4 are longer than TM1 and TM3 and protrude into the cytosolic domain, providing three of the nine histidine residues that coordinate the two metal ions, while the other histidine residues are provided by the soluble domain in this enzyme.
Pssm-ID: 425713 [Multi-domain] Cd Length: 252 Bit Score: 100.88 E-value: 4.67e-24
Cytochrome b5-like Heme/Steroid binding domain; This family includes heme binding domains from ...
78-150
3.76e-23
Cytochrome b5-like Heme/Steroid binding domain; This family includes heme binding domains from a diverse range of proteins. This family also includes proteins that bind to steroids. The family includes progesterone receptors. Many members of this subfamily are membrane anchored by an N-terminal transmembrane alpha helix. This family also includes a domain in some chitin synthases. There is no known ligand for this domain in the chitin synthases.
Pssm-ID: 459698 [Multi-domain] Cd Length: 74 Bit Score: 92.68 E-value: 3.76e-23
The Delta12 Fatty Acid Desaturase (Delta12-FADS)-like CD includes the integral-membrane ...
202-454
1.42e-14
The Delta12 Fatty Acid Desaturase (Delta12-FADS)-like CD includes the integral-membrane enzymes, delta-12 acyl-lipid desaturases, oleate 12-hydroxylases, omega3 and omega6 fatty acid desaturases, and other related proteins, found in a wide range of organisms including higher plants, green algae, diatoms, nematodes, fungi, and bacteria. The expression of these proteins appears to be temperature dependent: decreases in temperature result in increased levels of fatty acid desaturation within membrane lipids subsequently altering cell membrane fluidity. An important enzyme for the production of polyunsaturates in plants is the oleate delta-12 desaturase (Arabidopsis FAD2) of the endoplasmic reticulum. This enzyme accepts l-acyl-2-oleoyl-sn-glycero-3-phosphocholine as substrate and requires NADH:cytochrome b oxidoreductase, cytochrome b, and oxygen for activity. FAD2 converts oleate(18:1) to linoleate (18:2) and is closely related to oleate 12-hydroxylase which catalyzes the hydroxylation of oleate to ricinoleate. Plastid-bound desaturases (Arabidopsis delta-12 desaturase (FAD6), omega-3 desaturase (FAD8), omega-6 desaturase (FAD6)), as well as, the cyanobacterial thylakoid-bound FADSs require oxygen, ferredoxin, and ferredoxin oxidoreductase for activity. As in higher plants, the cyanobacteria delta-12 (DesA) and omega-3 (DesB) FADSs desaturate oleate (18:1) to linoleate (18:2) and linoleate (18:2) to linolenate (18:3), respectively. Omega-3 (DesB/FAD8) and omega-6 (DesD/FAD6) desaturases catalyze reactions that introduce a double bond between carbons three and four, and carbons six and seven, respectively, from the methyl end of fatty acids. As with other members of this superfamily, this domain family has extensive hydrophobic regions that would be capable of spanning the membrane bilayer at least twice. Comparison of sequences also reveals the existence of three regions of conserved histidine cluster motifs that contain eight histidine residues: HXXXH, HXX(X)HH, and HXXHH. These histidine residues are reported to be catalytically essential and proposed to be the ligands for the iron atoms contained within the homologue, stearoyl CoA desaturase. Mutation of any one of four of these histidines in the Synechocystis delta-12 acyl-lipid desaturase resulted in complete inactivity.
Pssm-ID: 239584 [Multi-domain] Cd Length: 222 Bit Score: 73.03 E-value: 1.42e-14
The membrane fatty acid desaturase (Membrane_FADS)-like CD includes membrane FADSs, alkane ...
217-289
7.25e-11
The membrane fatty acid desaturase (Membrane_FADS)-like CD includes membrane FADSs, alkane hydroxylases, beta carotene ketolases (CrtW-like), hydroxylases (CrtR-like), and other related proteins. They are present in all groups of organisms with the exception of archaea. Membrane FADSs are non-heme, iron-containing, oxygen-dependent enzymes involved in regioselective introduction of double bonds in fatty acyl aliphatic chains. They play an important role in the maintenance of the proper structure and functioning of biological membranes. Alkane hydroxylases are bacterial, integral-membrane di-iron enzymes that share a requirement for iron and oxygen for activity similar to that of membrane FADSs, and are involved in the initial oxidation of inactivated alkanes. Beta-carotene ketolase and beta-carotene hydroxylase are carotenoid biosynthetic enzymes for astaxanthin and zeaxanthin, respectively. This superfamily domain has extensive hydrophobic regions that would be capable of spanning the membrane bilayer at least twice. Comparison of these sequences also reveals three regions of conserved histidine cluster motifs that contain eight histidine residues: HXXX(X)H, HXX(X)HH, and HXXHH (an additional conserved histidine residue is seen between clusters 2 and 3). Spectroscopic and genetic evidence point to a nitrogen-rich coordination environment located in the cytoplasm with as many as eight histidines coordinating the two iron ions and a carboxylate residue bridging the two metals in the Pseudomonas oleovorans alkane hydroxylase (AlkB). In addition, the eight histidine residues are reported to be catalytically essential and proposed to be the ligands for the iron atoms contained within the rat stearoyl CoA delta-9 desaturase.
Pssm-ID: 238511 [Multi-domain] Cd Length: 122 Bit Score: 59.41 E-value: 7.25e-11
Beta-carotene hydroxylase (CrtR), the carotenoid zeaxanthin biosynthetic enzyme catalyzes the ...
202-289
1.80e-03
Beta-carotene hydroxylase (CrtR), the carotenoid zeaxanthin biosynthetic enzyme catalyzes the addition of hydroxyl groups to the beta-ionone rings of beta-carotene to form zeaxanthin and is found in bacteria and red algae. Carotenoids are important natural pigments; zeaxanthin and lutein are the only dietary carotenoids that accumulate in the macular region of the retina and lens. It is proposed that these carotenoids protect ocular tissues against photooxidative damage. CrtR does not show overall amino acid sequence similarity to the beta-carotene hydroxylases similar to CrtZ, an astaxanthin biosynthetic beta-carotene hydroxylase. However, CrtR does show sequence similarity to the green alga, Haematococcus pluvialis, beta-carotene ketolase (CrtW), which converts beta-carotene to canthaxanthin. Sequences of the CrtR_beta-carotene-hydroxylase domain family, as well as, the CrtW_beta-carotene-ketolase domain family appear to be structurally related to membrane fatty acid desaturases and alkane hydroxylases. They all share in common extensive hydrophobic regions that would be capable of spanning the membrane bilayer at least twice. Comparison of these sequences also reveals three regions of conserved histidine cluster motifs that contain eight histidine residues: HXXXH, HXXHH, and HXXHH. These histidine residues are reported to be catalytically essential and proposed to be the ligands for the iron atoms contained within homologs, stearoyl CoA desaturase and alkane hydroxylase.
Pssm-ID: 239591 [Multi-domain] Cd Length: 207 Bit Score: 39.66 E-value: 1.80e-03
Database: CDSEARCH/cdd Low complexity filter: no Composition Based Adjustment: yes E-value threshold: 0.01
References:
Wang J et al. (2023), "The conserved domain database in 2023", Nucleic Acids Res.51(D)384-8.
Lu S et al. (2020), "The conserved domain database in 2020", Nucleic Acids Res.48(D)265-8.
Marchler-Bauer A et al. (2017), "CDD/SPARCLE: functional classification of proteins via subfamily domain architectures.", Nucleic Acids Res.45(D)200-3.
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