Curcumin synthase 1 (CURS1) | |||||||||
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Identifiers | |||||||||
EC no. | 2.3.1.217 | ||||||||
CAS no. | 1245303-08-5 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
Gene Ontology | AmiGO / QuickGO | ||||||||
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Curcumin synthase 3 (CURS3) | |||||||||
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Identifiers | |||||||||
EC no. | 2.3.1.219 | ||||||||
CAS no. | 1245303-10-9 | ||||||||
Databases | |||||||||
IntEnz | IntEnz view | ||||||||
BRENDA | BRENDA entry | ||||||||
ExPASy | NiceZyme view | ||||||||
KEGG | KEGG entry | ||||||||
MetaCyc | metabolic pathway | ||||||||
PRIAM | profile | ||||||||
PDB structures | RCSB PDB PDBe PDBsum | ||||||||
Gene Ontology | AmiGO / QuickGO | ||||||||
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Curcumin synthase categorizes three enzyme isoforms (CURS1, 2, and 3), type III polyketide synthases (PKSs) present in the leaves and rhizome of the turmeric plant (Curcuma longa) [1] that synthesize curcumin. [2] CURS1-3 are responsible for the hydrolysis of feruloyldiketide-CoA, [3] previously produced in the curcuminoid pathway, and a decarboxylative condensation reaction [1] [2] that together comprise one of the final steps in the synthesis pathway for curcumin, demethoxycurcumin, and bisdemethoxycurcumin, the compounds that give turmeric both its distinctive yellow color, and traditional medical benefits. [4] CURS should not be confused with Curcuminoid Synthase (CUS), which catalyzes the one-pot synthesis of bisdemethoxycurcumin in Oryza sativa. [5]
Crystallization studies [6] have determined that curcumin synthase is a homodimer of ketosynthase subunits. [2] [7] Each includes a highly conserved Cys (164), His (303), Asn (336) catalytic triad, and CURS1 has been shown to exhibit the αβαβα folding pattern, [6] conserved features of type III PKSs. [7] [8] The catalytic triads are independent of each other and are contained in the center of each monomer, connected to the surface with a CoA binding tunnel. [6] While CURS1, 2, and 3 share approximately 80% amino acid sequence identity, their small structural differences account for their differences in preferred starter substrates and most prolific product. [1]
The well conserved catalytic triad sits at the end of a hydrophobic cavity, referred to as the CoA binding tunnel, that allows for the specificity of curcumin synthase for the CoA moiety. The triad, displayed in a PyMOL image below, despite being buried in each monomer, is connected to the surface of the binding tunnel, allowing interactions with substrates. The pockets of the protein show this tunnel and where the β-keto acid tail of feruloyl-CoA can fit into, which we can also see in the photo of the CoA binding tunnel reaching towards the catalytic triad. In addition to the catalytic triad, there are two conserved phenylalanine residues, Phe-215 and Phe-265, and a glycine, Gly-211, that contribute to the nature of the hydrophobicity pocket. The phenylalanines are named the “gatekeepers,” which allow for the correct tunnel width for CoA. The Gyl-211 can be mutated to affect the trafficking of this pocket, as bulkier residues can occupy the hydrophobic cavity. CURS1 has not been crystallized with CoA, but chalcone synthase, which is another type III PKS, has been shown bound to CoA. CHS and curcumin synthase have the same catalytic triad and CoA binding tunnel, so we can look at the nature of binding. The CoA is held tightly in the CoA binding tunnel in the image of conserved residues, showing where it can connect to these gatekeepers and traffic guards of important residues. [6]
Each CURS catalyzes the reactions necessary to convert a feruloyldiketide-CoA into a curcuminoid, but the three isoforms have preferred starter substrates and products. CURS1 converts feruloyldiketide-CoA esters into curcumin using feruloyl-CoA exclusively as a starter substrate. CURS2 produces both curcumin and demethoxycurcumin, favoring feruloyl-CoA as a starter, and CURS3 produces curcumin, demethoxycurcumin, and bisdemethoxycurcumin from either feruloyl-CoA or 4-coumaroyl-CoA as the starter substrate. [3] The fact that preferences of starter substrates vary between the three CURS is corroborated by carbon labeling studies confirming the incorporation of a variety of starter substrates into curcuminoid products in C. longa. [9]
Only the mechanism of CURS1 has been elucidated. In the first step, the feruloyl moiety of feruloyl-CoA is transferred to Cys (164) followed by feruloyldiketide-CoA entering the CoA binding tunnel and being hydrolyzed through an unknown mechanism to a β-keto acid. [6] The acid is then used as an extender substrate in the catalytic triad, where it undergoes decarboxylative condensation with the feruloyl moiety on Cys (164). This mechanism is thought to be identical to that of the decarboxylative condensation of malonyl-CoA in other type III PKSs. [6] The hydrolysis of the diketide has been shown to be the rate-limiting step of the enzyme. [6]
It was previously hypothesized that the curcumoid pathway employed two cinnamoyl-CoAs and one malonyl-CoA, but this was suggested against by the absence of a necessary intermediate such a pathway (bisdeshydroxybisdesmethoxycurcumin), [9] strengthening evidence for feruloyl-CoA or 4-coumaroyl-CoA as starter substrate in CURS.
The production of curcumin and its derivatives by CURS may be a defense mechanism of C. longa against internal and external threats. Curcumin is a potent antioxidant, as its phenolic structure, highest in activity in curcumin rather than its demethoxylated derivatives, [10] acts as a free-radical scavenging apparatus, eliminating free superoxides and DPPH from the plant's cells. [10] Curcumin synthase may also protect Curcuma longa from herbivores to some degree, as curcumin has a distinctively bitter taste: [10] studies show CURS1, 2 have higher expression in the leaves of C. longa than the rhizome [1] [11] while CURS3 shows equal expression in both locations. [1]
Research suggests that curcumin is an active anti-cancer molecule against cancers of brain, breast, bones, blood, gastrointestinal tract, genitourinary tract, as well as thoracic and gynecological cancers. [12] The molecule achieves this wide-range activity by up or down-regulating numerous receptors, kinases, growth factors, transcriptional factors, and inflammatory cytokines, among others, [12] thus its biosynthesis is of great interest to medicine.
For instance, curcumin inhibits mammalian nuclear factor κB (NF-κB) by preventing its translocation to the nucleus. [10] This inhibitory action upregulates the levels of preapoptotic and apoptotic cells, eliminating damaged cells, and discouraging abnormal growth patterns, as well as decreasing chemokine levels. [13] As activated NF-κB is associated with oxidative stress, [13] inhibition of the nuclear factor by curcumin is consistent with the chemical's role as an antioxidant. A homologous system to NF-κB signaling exists in plants, [14] evidence that curcumin may play a similar role in C. longa as it does in humans.
Curcumin syntheses in C. longa have been until recently, the only readily available synthesis method of curcumin. Today, laboratory syntheses are capable of producing the chemical, [15] and numerous teams are constructing curcumin analogues designed to target specific biological processes, such as the NFκB signaling pathway previously discussed. [16]
Turmeric or Curcuma longa, is a flowering plant in the ginger family Zingiberaceae. It is a perennial, rhizomatous, herbaceous plant native to the Indian subcontinent and Southeast Asia that requires temperatures between 20 and 30 °C and high annual rainfall to thrive. Plants are gathered each year for their rhizomes, some for propagation in the following season and some for consumption.
Curcumin is a bright yellow chemical produced by plants of the Curcuma longa species. It is the principal curcuminoid of turmeric, a member of the ginger family, Zingiberaceae. It is sold as a herbal supplement, cosmetics ingredient, food flavoring, and food coloring.
Glycogen synthase kinase 3 (GSK-3) is a serine/threonine protein kinase that mediates the addition of phosphate molecules onto serine and threonine amino acid residues. First discovered in 1980 as a regulatory kinase for its namesake, glycogen synthase (GS), GSK-3 has since been identified as a protein kinase for over 100 different proteins in a variety of different pathways. In mammals, including humans, GSK-3 exists in two isozymes encoded by two homologous genes GSK-3α (GSK3A) and GSK-3β (GSK3B). GSK-3 has been the subject of much research since it has been implicated in a number of diseases, including type 2 diabetes, Alzheimer's disease, inflammation, cancer, addiction and bipolar disorder.
Gingerol ([6]-gingerol) is a phenolic phytochemical compound found in fresh ginger that activates heat receptors on the tongue. It is normally found as a pungent yellow oil in the ginger rhizome, but can also form a low-melting crystalline solid. This chemical compound is found in all members of the Zingiberaceae family and is high in concentrations in the grains of paradise as well as an African Ginger species.
Methyltransferases are a large group of enzymes that all methylate their substrates but can be split into several subclasses based on their structural features. The most common class of methyltransferases is class I, all of which contain a Rossmann fold for binding S-Adenosyl methionine (SAM). Class II methyltransferases contain a SET domain, which are exemplified by SET domain histone methyltransferases, and class III methyltransferases, which are membrane associated. Methyltransferases can also be grouped as different types utilizing different substrates in methyl transfer reactions. These types include protein methyltransferases, DNA/RNA methyltransferases, natural product methyltransferases, and non-SAM dependent methyltransferases. SAM is the classical methyl donor for methyltransferases, however, examples of other methyl donors are seen in nature. The general mechanism for methyl transfer is a SN2-like nucleophilic attack where the methionine sulfur serves as the leaving group and the methyl group attached to it acts as the electrophile that transfers the methyl group to the enzyme substrate. SAM is converted to S-Adenosyl homocysteine (SAH) during this process. The breaking of the SAM-methyl bond and the formation of the substrate-methyl bond happen nearly simultaneously. These enzymatic reactions are found in many pathways and are implicated in genetic diseases, cancer, and metabolic diseases. Another type of methyl transfer is the radical S-Adenosyl methionine (SAM) which is the methylation of unactivated carbon atoms in primary metabolites, proteins, lipids, and RNA.
Pinosylvin is an organic compound with the formula C6H5CH=CHC6H3(OH)2. A white solid, it is related to trans-stilbene, but with two hydroxy groups on one of the phenyl substituents. It is very soluble in many organic solvents, such as acetone.
The calicheamicins are a class of enediyne antitumor antibiotics derived from the bacterium Micromonospora echinospora, with calicheamicin γ1 being the most notable. It was isolated originally in the mid-1980s from the chalky soil, or "caliche pits", located in Kerrville, Texas. The sample was collected by a scientist working for Lederle Labs. It is extremely toxic to all cells and, in 2000, a CD33 antigen-targeted immunoconjugate N-acetyl dimethyl hydrazide calicheamicin was developed and marketed as targeted therapy against the non-solid tumor cancer acute myeloid leukemia (AML). A second calicheamicin-linked monoclonal antibody, inotuzumab ozogamicin an anti-CD22-directed antibody-drug conjugate, was approved by the U.S. Food and Drug Administration on August 17, 2017, for use in the treatment of adults with relapsed or refractory B-cell precursor acute lymphoblastic leukemia. Calicheamicin γ1 and the related enediyne esperamicin are the two of the most potent antitumor agents known.
Polyketide synthases (PKSs) are a family of multi-domain enzymes or enzyme complexes that produce polyketides, a large class of secondary metabolites, in bacteria, fungi, plants, and a few animal lineages. The biosyntheses of polyketides share striking similarities with fatty acid biosynthesis.
Chalcone synthase or naringenin-chalcone synthase (CHS) is an enzyme ubiquitous to higher plants and belongs to a family of polyketide synthase enzymes (PKS) known as type III PKS. Type III PKSs are associated with the production of chalcones, a class of organic compounds found mainly in plants as natural defense mechanisms and as synthetic intermediates. CHS was the first type III PKS to be discovered. It is the first committed enzyme in flavonoid biosynthesis. The enzyme catalyzes the conversion of 4-coumaroyl-CoA and malonyl-CoA to naringenin chalcone.
In molecular biology, Beta-ketoacyl-ACP synthase EC 2.3.1.41, is an enzyme involved in fatty acid synthesis. It typically uses malonyl-CoA as a carbon source to elongate ACP-bound acyl species, resulting in the formation of ACP-bound β-ketoacyl species such as acetoacetyl-ACP.
Thiolases, also known as acetyl-coenzyme A acetyltransferases (ACAT), are enzymes which convert two units of acetyl-CoA to acetoacetyl CoA in the mevalonate pathway.
Guanosine monophosphate synthetase, also known as GMPS is an enzyme that converts xanthosine monophosphate to guanosine monophosphate.
Doxorubicin (DXR) is a 14-hydroxylated version of daunorubicin, the immediate precursor of DXR in its biosynthetic pathway. Daunorubicin is more abundantly found as a natural product because it is produced by a number of different wild type strains of streptomyces. In contrast, only one known non-wild type species, streptomyces peucetius subspecies caesius ATCC 27952, was initially found to be capable of producing the more widely used doxorubicin. This strain was created by Arcamone et al. in 1969 by mutating a strain producing daunorubicin, but not DXR, at least in detectable quantities. Subsequently, Hutchinson's group showed that under special environmental conditions, or by the introduction of genetic modifications, other strains of streptomyces can produce doxorubicin. His group has also cloned many of the genes required for DXR production, although not all of them have been fully characterized. In 1996, Strohl's group discovered, isolated and characterized dox A, the gene encoding the enzyme that converts daunorubicin into DXR. By 1999, they produced recombinant Dox A, a Cytochrome P450 oxidase, and found that it catalyzes multiple steps in DXR biosynthesis, including steps leading to daunorubicin. This was significant because it became clear that all daunorubicin producing strains have the necessary genes to produce DXR, the much more therapeutically important of the two. Hutchinson's group went on to develop methods to improve the yield of DXR, from the fermentation process used in its commercial production, not only by introducing Dox A encoding plasmids, but also by introducing mutations to deactivate enzymes that shunt DXR precursors to less useful products, for example baumycin-like glycosides. Some triple mutants, that also over-expressed Dox A, were able to double the yield of DXR. This is of more than academic interest because at that time DXR cost about $1.37 million per kg and current production in 1999 was 225 kg per annum. More efficient production techniques have brought the price down to $1.1 million per kg for the non-liposomal formulation. Although DXR can be produced semi-synthetically from daunorubicin, the process involves electrophilic bromination and multiple steps and the yield is poor. Since daunorubicin is produced by fermentation, it would be ideal if the bacteria could complete DXR synthesis more effectively.
A curcuminoid is a linear diarylheptanoid, a relatively small class of plant secondary metabolites that includes curcumin, demethoxycurcumin, and bisdemethoxycurcumin, all isolated from turmeric. These compounds are natural phenols and produce a pronounced yellow color that is often used to color foods and medicines. Curcumin is obtained from the root of turmeric.
ATP citrate synthase (also ATP citrate lyase (ACLY)) is an enzyme that in animals represents an important step in fatty acid biosynthesis. By converting citrate to acetyl-CoA, the enzyme links carbohydrate metabolism, which yields citrate as an intermediate, with fatty acid biosynthesis, which consumes acetyl-CoA. In plants, ATP citrate lyase generates cytosolic acetyl-CoA precursors of thousands of specialized metabolites, including waxes, sterols, and polyketides.
Desmethoxycurcumin is a curcuminoid found in turmeric. Commercial grade curcumin contains a mixture of curcuminoids.
Germicidins are a groups of natural products arising from Streptomyces species that acts as autoregulatory inhibitor of spore germination. In Streptomyces viriochromogenes, low concentrations inhibit germination of its own arthrospores, and higher concentrations inhibit porcine Na+/K+ -activated ATPase. Inhibitory effects on germination are also observed when germicidin from Streptomyces is applied to Lepidium sativum. Germicidins and other natural products present potential use as pharmaceuticals, and in this case, those with possible antibiotic or antifungal activity.
The diarylheptanoids are a relatively small class of plant secondary metabolites. Diarylheptanoids consist of two aromatic rings joined by a seven carbons chain (heptane) and having various substituents. They can be classified into linear (curcuminoids) and cyclic diarylheptanoids. The best known member is curcumin, which is isolated from turmeric and is known as food coloring E100. Some other Curcuma species, such as Curcuma comosa also produce diarylheptanoids.
Ketoacyl synthases (KSs) catalyze the condensation reaction of acyl-CoA or acyl-acyl ACP with malonyl-CoA to form 3-ketoacyl-CoA or with malonyl-ACP to form 3-ketoacyl-ACP. This reaction is a key step in the fatty acid synthesis cycle, as the resulting acyl chain is two carbon atoms longer than before. KSs exist as individual enzymes, as they do in type II fatty acid synthesis and type II polyketide synthesis, or as domains in large multidomain enzymes, such as type I fatty acid synthases (FASs) and polyketide synthases (PKSs). KSs are divided into five families: KS1, KS2, KS3, KS4, and KS5.
Tumerones are a group of related chemical compounds of the sesquiterpene class. They are found in turmeric, from which they derive their name, as well as other related plants such as Curcuma caesia. There are multiple structural types of turmerones which differ in the number and placement of double bonds including α-tumerone, β-turmerone, and ar-turmerone. Each of these types consists of multiple stereoisomers.