The Delta9 Fatty Acid Desaturase (Delta9-FADS)-like CD includes the delta-9 and delta-11 acyl CoA desaturases found in various eukaryotes including vertebrates, insects, higher plants, and fungi. The delta-9 acyl-lipid desaturases are found in a wide range of bacteria. These enzymes play essential roles in fatty acid metabolism and the regulation of cell membrane fluidity. Acyl-CoA desaturases are the enzymes involved in the CoA-bound desaturation of fatty acids. Mammalian stearoyl-CoA delta-9 desaturase is a key enzyme in the biosynthesis of monounsaturated fatty acids, and in yeast, the delta-9 acyl-CoA desaturase (OLE1) reaction accounts for all de nova unsaturated fatty acid production in Saccharomyces cerevisiae. These non-heme, iron-containing, ER membrane-bound enzymes are part of a three-component enzyme system involving cytochrome b5, cytochrome b5 reductase, and the delta-9 fatty acid desaturase. This complex catalyzes the NADH- and oxygen-dependent insertion of a cis double bond between carbons 9 and 10 of the saturated fatty acyl substrates, palmitoyl (16:0)-CoA or stearoyl (18:0)-CoA, yielding the monoenoic products palmitoleic (16:l) or oleic (18:l) acids, respectively. In cyanobacteria, the biosynthesis of unsaturated fatty acids is initiated by delta 9 acyl-lipid desaturase (DesC) which introduces the first double bond at the delta-9 position of a saturated fatty acid that has been esterified to a glycerolipid. 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: HXXXXH, HXXHH, and H/QXXHH. These 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. Some eukaryotic (Fungi, Euglenozoa, Mycetozoa, Rhodophyta) desaturase domains have an adjacent C-terminal cytochrome b5-like domain.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177  58 WWGIPVVLVGNFIFGSLGINLGYHRMLTHSAAKFPKALERLWVLCGVCSLEGSPLWWVCTHRIHHQHSDDEGDPHSPREH 137
Cdd:cd03505     1 SWATLVFLVLYYLLTGLGITAGYHRLWAHRSFKAPKPLRIFLAILGSLAGQGSPLWWVADHRLHHRYSDTDGDPHSPKRG 80

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177 138 FYWGHMEWIytaderrqkldtyaryvpdlmgdkflrwlhrgekwllvwaahvaalaalgfgagflfsdtaagavqfgvqw 217
Cdd:cd03505    81 FWFSHVGWL----------------------------------------------------------------------- 89

                         170       180       190       200       210       220       230       240
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177 218 fmwAVVVRTVYVWHITWLVNSAAHRWGYRSYNTGDRSTNNWVVALLTNGEGWHNNHHAAPRACSQGHRWWELDLTFTFVR 297
Cdd:cd03505    90 ---GGLLRIVLVLHATWLVNSLAHMWGYRPYDTRDTSRNNWWVALLTFGEGWHNNHHAFPGDARNGLKWYQIDPTKWVIR 166

                         250
                  ....*....|.
gi 1728916177 298 ALQLVGLAWNI 308
Cdd:cd03505   167 LLEKLGLAWDL 177

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.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177  57 VWWGIPVVLVGNFIFGSLGINLG---YHRMLTHSAAKFPKALERLWVLCGVCSLeGSPLWWVCTHRIHHQH-SDDEGDPH 132
Cdd:pfam00487   1 SWLALLLALLLGLFLLGITGSLAheaSHGALFKKRRLNRWLNDLLGRLAGLPLG-ISYSAWRIAHLVHHRYtNGPDKDPD 79

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177 133 SPREHFYWGHMEWIYTADERRQKLDTYARYVPDLMGDKFL---RWLHRGEKWLLVWAAHVAALAALGFGAgflfsdtAAG 209
Cdd:pfam00487  80 TAPLASRFRGLLRYLLRWLLGLLVLAWLLALVLPLWLRRLarrKRPIKSRRRRWRLIAWLLLLAAWLGLW-------LGF 152

                         170       180       190       200       210       220       230       240
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177 210 AVQFGVQWFMWAVVVRTVYVWHITW--LVNSAAHRWGYRSY-NTGDRSTNNWVVALLTNGEGWHNNHHAAPracsqGHRW 286
Cdd:pfam00487 153 LGLGGLLLLLWLLPLLVFGFLLALIfnYLEHYGGDWGERPVeTTRSIRSPNWWLNLLTGNLNYHIEHHLFP-----GVPW 227

                         250
                  ....*....|...
gi 1728916177 287 WELDLTFTFVRAL 299
Cdd:pfam00487 228 YRLPKLHRRLREA 240

The Delta9 Fatty Acid Desaturase (Delta9-FADS)-like CD includes the delta-9 and delta-11 acyl CoA desaturases found in various eukaryotes including vertebrates, insects, higher plants, and fungi. The delta-9 acyl-lipid desaturases are found in a wide range of bacteria. These enzymes play essential roles in fatty acid metabolism and the regulation of cell membrane fluidity. Acyl-CoA desaturases are the enzymes involved in the CoA-bound desaturation of fatty acids. Mammalian stearoyl-CoA delta-9 desaturase is a key enzyme in the biosynthesis of monounsaturated fatty acids, and in yeast, the delta-9 acyl-CoA desaturase (OLE1) reaction accounts for all de nova unsaturated fatty acid production in Saccharomyces cerevisiae. These non-heme, iron-containing, ER membrane-bound enzymes are part of a three-component enzyme system involving cytochrome b5, cytochrome b5 reductase, and the delta-9 fatty acid desaturase. This complex catalyzes the NADH- and oxygen-dependent insertion of a cis double bond between carbons 9 and 10 of the saturated fatty acyl substrates, palmitoyl (16:0)-CoA or stearoyl (18:0)-CoA, yielding the monoenoic products palmitoleic (16:l) or oleic (18:l) acids, respectively. In cyanobacteria, the biosynthesis of unsaturated fatty acids is initiated by delta 9 acyl-lipid desaturase (DesC) which introduces the first double bond at the delta-9 position of a saturated fatty acid that has been esterified to a glycerolipid. 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: HXXXXH, HXXHH, and H/QXXHH. These 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. Some eukaryotic (Fungi, Euglenozoa, Mycetozoa, Rhodophyta) desaturase domains have an adjacent C-terminal cytochrome b5-like domain.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177  58 WWGIPVVLVGNFIFGSLGINLGYHRMLTHSAAKFPKALERLWVLCGVCSLEGSPLWWVCTHRIHHQHSDDEGDPHSPREH 137
Cdd:cd03505     1 SWATLVFLVLYYLLTGLGITAGYHRLWAHRSFKAPKPLRIFLAILGSLAGQGSPLWWVADHRLHHRYSDTDGDPHSPKRG 80

                          90       100       110       120       130       140       150       160
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177 138 FYWGHMEWIytaderrqkldtyaryvpdlmgdkflrwlhrgekwllvwaahvaalaalgfgagflfsdtaagavqfgvqw 217
Cdd:cd03505    81 FWFSHVGWL----------------------------------------------------------------------- 89

                         170       180       190       200       210       220       230       240
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177 218 fmwAVVVRTVYVWHITWLVNSAAHRWGYRSYNTGDRSTNNWVVALLTNGEGWHNNHHAAPRACSQGHRWWELDLTFTFVR 297
Cdd:cd03505    90 ---GGLLRIVLVLHATWLVNSLAHMWGYRPYDTRDTSRNNWWVALLTFGEGWHNNHHAFPGDARNGLKWYQIDPTKWVIR 166

                         250
                  ....*....|.
gi 1728916177 298 ALQLVGLAWNI 308
Cdd:cd03505   167 LLEKLGLAWDL 177

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.

                          10        20        30        40        50        60        70        80
                  ....*....|....*....|....*....|....*....|....*....|....*....|....*....|....*....|
gi 1728916177  62 PVVLVGNFIFGSLGINLGYHRmLTHSAAKFPKALERLWVLCGVCSLEGSPLWWVCTHRIHHQHSD-DEGDPHSPRE--HF 138
Cdd:cd01060     1 LLLALLLGLLGGLGLTVLAHE-LGHRSFFRSRWLNRLLGALLGLALGGSYGWWRRSHRRHHRYTNtPGKDPDSAVNylEH 79

                  ....*..
gi 1728916177 139 YWGHMEW 145
Cdd:cd01060    80 YGGDRPF 86

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.

                          10        20        30        40        50
                  ....*....|....*....|....*....|....*....|....*....|.
gi 1728916177 234 WLVNSAAHRWGYRSYN-------TGDRSTNNWVVALLTNGEGWHNNHHAAP 277
Cdd:cd01060    72 SAVNYLEHYGGDRPFDtdgewlrTTDNSRNGWLNLLLTGGLGYHNEHHLFP 122