>gnl|CDD|173836 cd00867, Trans_IPPS, Trans-Isoprenyl Diphosphate Synthases. Trans-Isoprenyl Diphosphate Synthases (Trans_IPPS) of class 1 isoprenoid biosynthesis enzymes which either synthesis geranyl/farnesyl diphosphates (GPP/FPP) or longer chained products from isoprene precursors, isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), or use geranyl (C10)-, farnesyl (C15)-, or geranylgeranyl (C20)-diphosphate as substrate. These enzymes produce a myriad of precursors for such end products as steroids, cholesterol, sesquiterpenes, heme, carotenoids, retinoids, diterpenes, ubiquinone, and archaeal ether linked lipids; and are widely distributed among archaea, bacteria, and eukareya. The enzymes in this family share the same 'isoprenoid synthase fold' and include the head-to-tail (HT) IPPS which catalyze the successive 1'-4 condensation of the 5-carbon IPP to the growing isoprene chain to form linear, all-trans, C10-, C15-, C20- C25-, C30-, C35-, C40-, C45-, or C50-isoprenoid diphosphates. The head-to-head (HH) IPPS catalyze the successive 1'-1 condensation of 2 farnesyl or 2 geranylgeranyl isoprenoid diphosphates. Isoprenoid chain elongation reactions proceed via electrophilic alkylations in which a new carbon-carbon single bond is generated through interaction between a highly reactive electron-deficient allylic carbocation and an electron-rich carbon-carbon double bond. The catalytic site consists of a large central cavity formed by mostly antiparallel alpha helices with two aspartate-rich regions located on opposite walls. These residues mediate binding of prenyl phosphates via bridging Mg2+ ions, inducing proposed conformational changes that close the active site to solvent, stabilizing reactive carbocation intermediates. Mechanistically and structurally distinct, cis-IPPS are not included in this CD. Length = 236

 Score =  196 bits (501), Expect = 6e-51
 Identities = 82/207 (39%), Positives = 120/207 (57%), Gaps = 2/207 (0%)

Query: 45  LRPMLTLATALMLEYRGDNHVLLACAIEFIHTATLLHDDVVDDSALRRGKVAARLV-WGN 103
            RP+L L  A  L    +  + LA A+E +H A+L+HDD+VDDS LRRGK  A L  +GN
Sbjct: 1   SRPLLVLLLARALGGDLEAALRLAAAVELLHAASLVHDDIVDDSDLRRGKPTAHLRRFGN 60

Query: 104 QTSVLVGDFLLSQAFCMVIETKSQEALEALSLVACTLAEGELRQLSLSKNLDVTEEDYLH 163
             ++L GD+LL++AF ++       ALE  +     L EG+   L   ++   T ++YL 
Sbjct: 61  ALAILAGDYLLARAFQLLARLGYPRALELFAEALRELLEGQALDLEFERDTYETLDEYLE 120

Query: 164 VIKSKTAVLFSAALEVSSLIAGVQNSVRQALKSYGMNLGIAFQLVDDVLDYRGEVNEMGK 223
             + KTA L      + + ++G  +   +ALK YG  LG+AFQL DD+LD  G+  E+GK
Sbjct: 121 YCRYKTAGLVGLLCLLGAGLSGADDEQAEALKDYGRALGLAFQLTDDLLDVFGDAEELGK 180

Query: 224 NIGEDFRNGKPTLPVILAFQRGTKREK 250
            +G D R G+ TLPVILA +R  +  +
Sbjct: 181 -VGSDLREGRITLPVILARERAAEYAE 206