IPP belongs to the KLHL family. It binds to actin through its kelch repeat domain []. Its function is not clear. The KLHL (Kelch-like) proteins generally have a BTB/POZ domain, a BACK domain, and five to six Kelch motifs. They constitute a subgroup at the intersection between the BTB/POZ domain and Kelch domain superfamilies. The BTB/POZ domain facilitates protein binding [], while the Kelch domain (repeats) form β-propellers. The Kelch superfamily of proteins can be subdivided into five groups: (1) N-propeller, C-dimer proteins, (2) N-propeller proteins, (3) propeller proteins, (4) N-dimer, C-propeller proteins, and (5) C-propeller proteins. KLHL family members belong to the N-dimer, C-propeller subclass of Kelch repeat proteins []. In addition to BTB/POZ and Kelch domains, the KLHL family members contain a BACK domain, first described as a130-residue region of conservation observed amongst BTB-Kelch proteins []. Many of the Kelch-like proteins have been identified as adaptors for the recruitment of substrates to Cul3-based E3 ubiquitin ligases [, ].
tRNA dimethylallyltransferase alternative names include delta(2)-isopentenylpyrophosphate transferase, IPP transferral and 2-methylthio-N6-isopentyladenosine tRNA modification enzyme. This enzyme catalyses the first step in the modification of an adenosine near the anticodon to 2-methylthio-N6-isopentyladenosine [].Plants have two classes of isopentenyltransferases (IPTs): ATP/ADP isopentenyltransferases (IPT1, 3, 4-8) and tRNA IPTs (IPT2 and 9) []. Both types are included in this family.
This entry represents the bacterial and archaeal isopentenyl-diphosphate delta-isomerase (IPP isomerase). IPP isomerase catalyses the interconversion of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP), and is a key enzyme in the biosynthesis of isoprenoids via the mevalonate pathway. The bacterial and archaeal IPP isomerase (type 2 enzyme) differs from that found in eukaryotes (type 1 enzyme), and requires NADPH, magnesium, and FMN for activity [, ].
In prokaryotes, undecaprenyl diphosphate synthase (UPP synthase, di-trans-poly-cis-decaprenylcistransferase or ditrans,polycis-undecaprenyl-diphosphate synthase ()), catalyzes the formation of the carrier lipid undecaprenyl pyrophosphate (UPP) in bacterial cell wall peptidoglycan biosynthesis from isopentenyl pyrophosphate (IPP) [, , , , , , , , , , , , , ]. Cis (Z)-Isoprenyl diphosphate synthase (cis-IPPS) catalyzes the successive 1'-4 condensation of the IPP molecule to trans,trans-farnesyl diphosphate (FPP) or to cis,trans-FPP to form long-chain polyprenyl diphosphates. A few can also catalyze the condensation of IPP to trans-geranyl diphosphate to form the short-chain cis,trans- FPP. cis-IPPS form homodimers and are mechanistically and structurally distinct from trans-IPPS, which lack the DDXXD motifs, yet require Mg2+for activity. Homologues are also found in archaebacteria and include a number of uncharacterised proteins including some from yeasts.This entry also matches related enzymes that transfer alkyl groups, such as dehydrodolichyl diphosphate synthase from eukaryotes, which catalyzes the formation of the polyisoprenoid glycosyl carrier lipid dolichyl monophosphate.
This entry represents type 1 of two non-homologous families of the enzyme isopentenyl-diphosphate delta-isomerase (IPP isomerase; ). IPP isomerase is a member of the Nudix hydrolase superfamily, and is a key enzyme in the isoprenoid biosynthetic pathway. It catalyses the interconversion of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate. Dimethylallyl phosphate is the initial substrate for the biosynthesis of carotenoids and other long chain isoprenoids []. IPP is an essential building block for many compounds, including enzyme cofactors, sterols, and prenyl groups. This enzyme interconverts isopentenyl diphosphate and dimethylallyl diphosphate. The enzyme requires one Mn2+ or Mg2+ ion in its active site to fold into an active conformation and also contains the Nudix motif, a highly conserved 23-residue block (GX5EX7REUXEEXGU, where U = I, L or V), that functions as a metal binding and catalytic site. The metal binding site is present within the active site and plays structural and catalytical roles. IPP isomerase is well represented in several bacteria, archaebacteria and eukaryotes, including fungi, mammals and plants. Despite sequence variations (mainly at the N terminus), the core structure is highly conserved [].
2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase (IspD) catalyses the formation of 4-diphosphocytidyl-2-C-methyl-D-erythritol from CTP and 2-C-methyl-D-erythritol 4-phosphate (MEP) in the deoxyxylulose pathway of isopentenyl diphosphate (IPP) biosynthesis []. This mevalonate independent pathway that utilizes pyruvate and glyceraldehydes 3-phosphate as starting materials for production of IPP occurs in a variety of bacteria, archaea and plant cells, but is absent in mammals. The isoprenoid pathway is a well known target for anti-infective drug development [, ]. In about twenty percent of bacterial genomes, this protein occurs as IspDF, a bifunctional fusion protein.
In prokaryotes, undecaprenyl diphosphate synthase (UPP synthase or di-trans-poly-cis-decaprenylcistransferase ()), catalyzes the formation of the carrier lipid undecaprenyl pyrophosphate (UPP) in bacterial cell wall peptidoglycan biosynthesis from isopentenyl pyrophosphate (IPP) [, , , , , , , , , , , , , ]. Cis (Z)-Isoprenyl diphosphate synthase (cis-IPPS) catalyzes the successive 1'-4 condensation of the IPP molecule to trans,trans-farnesyl diphosphate (FPP) or to cis,trans-FPP to form long-chain polyprenyl diphosphates. A few can also catalyze the condensation of IPP to trans-geranyl diphosphate to form the short-chain cis,trans- FPP. cis-IPPS form homodimers and are mechanistically and structurally distinct from trans-IPPS, which lack the DDXXD motifs, yet require Mg2+for activity. Homologues are also found in archaebacteria and include a number of uncharacterised proteins including some from yeasts.The structure of diphosphate synthase has three layers (alpha/beta/alpha) with parallel β-sheet of six strands.This entry also matches related enzymes that transfer alkyl groups, such as dehydrodolichyl diphosphate synthase from eukaryotes, which catalyzes the formation of the polyisoprenoid glycosyl carrier lipid dolichyl monophosphate.
The pseudokinase domain shows similarity to protein kinases but lacks crucial residues for catalytic activity. Integrin linked kinase (ILK) contains N-terminal ankyrin repeats, a Pleckstrin Homology (PH) domain, and a C-terminal pseudokinase domain. It is a component of the IPP (ILK/PINCH/Parvin) complex that couples beta integrins to the actin cytoskeleton, and plays important roles in cell adhesion, spreading, invasion, and migration []. ILK was initially thought to be an active kinase despite the lack of key conserved residues because of in vitro studies showing that it can phosphorylate certain protein substrates. However, in vivo experiments in Caenorhabditis elegans, Drosophila melanogaster, and mice (ILK-null and knock-in) proved that ILK is not an active kinase []. In addition to actin cytoskeleton regulation, ILK also influences the microtubule network and mitotic spindle orientation [, ]. The pseudokinase domain of ILK binds several adaptor proteins including the parvins and paxillin [, ].
This family consists of cytidylyltransferases IspD and TarI.2-C-methyl-D-erythritol 4-phosphate cytidylyltransferase (IspD) catalyses the formation of 4-diphosphocytidyl-2-C-methyl-D-erythritol from CTP and 2-C-methyl-D-erythritol 4-phosphate (MEP) in the deoxyxylulose pathway of isopentenyl diphosphate (IPP) biosynthesis []. This mevalonate independent pathway that utilizes pyruvate and glyceraldehydes 3-phosphate as starting materials for production of IPP occurs in a variety of bacteria, archaea and plant cells, but is absent in mammals. The isoprenoid pathway is a well known target for anti-infective drug development [, ]. In about twenty percent of bacterial genomes, this protein occurs as IspDF, a bifunctional fusion protein.Ribitol-5-phosphate cytidylyltransferase (TarI) is required for the synthesisof activated ribitol via the wall teichoic acid biosynthesis pathway. The enzyme catalyzes the transfer of the cytidylyl group of CTP to D-ribitol 5-phosphate to form CDP-ribitol [].The human IspD (known as D-ribitol-5-phosphate cytidylyltransferase or isoprenoid synthase domain-containing protein) shows a canonical N-terminal cytidyltransferase domain linked to a C-terminal domain that is absent in cytidyltransferase homologues. It has cytidyltransferase activity toward pentose phosphates, including ribulose 5-phosphate, ribose 5-phosphate, and ribitol 5-phosphate. It is implicated in dystroglycan O-mannosylation [, ].
Proteins in this entry are members of the radical SAM superfamily of enzymes that utilise an iron-sulphur redox cluster and S-adenosylmethionine to carry out diverse radical mediated reactions []. This group of proteins are frequently encoded in the same locus as squalene-hopene cyclase (SHC, ) and other proteins associated with the biosynthesis of hopanoid natural products. The linkage between SHC and this radical SAM enzyme is strong; one is nearly always observed in the same genome where the other is found. A hopanoid biosynthesis locus was described in Zymomonas mobilis consisting of the genes for HpnA-E and SHC (HpnF) []. Continuing past SHC are the genes for a phosphorylase enzyme (ZMO0873, i.e. HpnG, ) and this radical SAM enzyme (ZMO0874) which we name here HpnH. Granted, in Z. mobilis, HpnH is in a convergent orientation with respect to HpnA-G, but one gene beyond HpnH and running in the same convergent direction is IspH (ZM0875, 4-hydroxy-3-methylbut-2-enyl diphosphate reductase), an essential enzyme of IPP biosynthesis and therefore essential for the biosynthesis of hopanoids. One of the well-described hopanoid intermediates is bacteriohopanetetrol. In the conversion from hopene several reactions must occur in the side chain for which a radical mechanism might be reasonable. These include the four (presumably anaerobic) hydroxylations and a methyl shift.
This group of enzymes belongs to the GHMP kinase domain superfamily. GHMP kinases are a unique class of ATP-dependent enzymes (the abbreviation of which refers to the original members: galactokinase, homoserine kinase, mevalonate kinase, and phosphomevalonate kinase) []. Enzymes belonging to this superfamily contain three well-conserved motifs, the second of which has the typical sequence Pro-X-X-X-Gly-Leu-X-Ser-Ser-Ala and is involved in ATP binding []. The phosphate binding loop in GHMP kinases is distinct from the classical P-loops found in many ATP/GTP binding proteins. The bound ADP molecule adopts a rare syn conformation and is in the opposite orientation from those bound to the P-loop-containing proteins []. GHMP kinases display a distinctly bilobal appearance with their N-terminal subdomains dominated by a mixed β-sheet flanked on one side by α-helices and their C-terminal subdomains containing a four stranded anti-parallel β-sheet [, , , ]. Diphosphomevalonate decarboxylase (mevalonate pyrophosphate decarboxylase, () catalyzes the decarboxylation of mevalonate pyrophosphate to isopentyl pyrophosphate (IPP) [], the last step in the synthesis of IPP in the mevalonate pathway. In archaea, an alternate pathway involves decarboxylation of mevalonate monophosphate instead of diphosphomevalonate []. Mevalonate is a key intermediate in the biosynthesis of sterols and non-sterol isoprenes in the mevalonate pathway. In mammals, the majority of mevalonate is converted into cholesterol.ATP + (R)-5-diphosphomevalonate = ADP + phosphate + isopentenyl diphosphate + CO2
This group of enzymes belongs to the GHMP kinase domain superfamily. GHMP kinases are a unique class of ATP-dependent enzymes (the abbreviation of which refers to the original members: galactokinase, homoserine kinase, mevalonate kinase, and phosphomevalonate kinase) []. Enzymes belonging to this superfamily contain three well-conserved motifs, the second of which has the typical sequence Pro-X-X-X-Gly-Leu-X-Ser-Ser-Ala and is involved in ATP binding[]. The phosphate binding loop in GHMP kinases is distinct from the classical P-loops found in many ATP/GTP binding proteins. The bound ADP molecule adopts a rare syn conformation and is in the opposite orientation from those bound to the P-loop-containing proteins []. GHMP kinases display a distinctly bilobal appearance with their N-terminal subdomains dominated by a mixed β-sheet flanked on one side by α-helices and their C-terminal subdomains containing a four stranded anti-parallel β-sheet [, , , ]. Diphosphomevalonate decarboxylase (mevalonate pyrophosphate decarboxylase, () catalyzes the decarboxylation of mevalonate pyrophosphate to isopentyl pyrophosphate (IPP) [], the last step in the synthesis of IPP in the mevalonate pathway. In archaea, an alternate pathway involves decarboxylation of mevalonate monophosphate instead of diphosphomevalonate []. Mevalonate is a key intermediate in the biosynthesis of sterols and non-sterol isoprenes in the mevalonate pathway. In mammals, the majority of mevalonate is converted into cholesterol.ATP + (R)-5-diphosphomevalonate = ADP + phosphate + isopentenyl diphosphate + CO2 The classical mevalonate (MVA) pathway involves decarboxylation of mevalonate diphosphate, while an alternate pathway involves decarboxylation of mevalonate monophosphate. The enzyme responsible is known as phosphomevalonate decarboxylase [].
Terpenes are among the largest groups of natural products and include compounds such as vitamins, cholesterol and carotenoids. The biosynthesis of all terpenoids begins with one or both of the two C5 precursors of the pathway: isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). In animals, fungi, and certain bacteria, the synthesis of IPP and DMAPP occurs via the well-known mevalonate pathway, however, a second, nonmevalonate terpenoid pathway has been identified in many eubacteria, algae, malaria parasite and the chloroplasts of higher plants [, , ].LytB(IspH) is the last enzyme in the biosynthesis of isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP) in the 1-deoxy-d-xylulose-5-phosphate (DOXP, the nonmevalonate pathway, also known as MEP) pathway []. This enzyme contains a [4Fe-4S]cluster and forms a stable complex with ferredoxin, which suggests that ferredoxin/ferredoxin-NADP+ reductase redox system serves as the physiological electron donor for LytB []. Escherichia coli LytB protein had been found to regulate the activity of RelA (guanosine 3',5'-bispyrophosphate synthetase I), which in turn controls the level of a regulatory metabolite. It is involved in penicillin tolerance and the stringent response [].
