Microorganisms isoprenoid

Carotenoids are isoprenoid compounds that are biosynthesized only by plants and microorganisms. Some carotenoids (a- and p-carotene, p-cryptoxanthine) can be cleaved into vitamin A (retinol) by an enzyme in the small intestine. Carotenoids have been reported to present some effects in the prevention of cardiovascular diseases [410] and in the prevention of some kind of cancers [411]. Furthermore, antioxidant activity has been widely reported [411-414] but a switch to pro-oxidant activity can occur as a function of oxygen concentration [415,416]. 

From the many enzymes that are known to make and break C-C bonds, we first chose the two transferases, transketolase (TKT) and transaldolase (TAL), both from the Gram-negative bacterium Escherichia coli. While project B21 evolved, we learned that this microorganism holds other and so far unknown enzymes which are of interest for asymmetric syntheses. One transketolase-like enzyme, 1-deoxy-D-xylulose 5-phosphate synthase (DXS), turned out to be the first enzyme of a novel biosynthetic pathway leading to isoprenoids in bacteria, algae, and plants. The other, fructose 6-phosphate aldolase (ESA) - while similar to transaldolase - allows the direct use of the inexpensive dihydroxyacetone in aldol condensations. 

Kerogens isolated from the Fig Tree cherts produced very complex mixtures of pyrolysis products, dominated by a series of methyl branched alkenes with each member of the series having 3 carbon atoms more than the previous member. At each carbon number a highly complex mixture of branched alkanes and alkenes plus various substituted aromatic compounds was found. The highly branched structures may have actually incorporated isoprenoids originally present in the Precambrian microorganisms (Philp Van DeMent, 1983)6>. 

Microorganisms and fungi are an especially rich source of isoprenoids of the most diverse structures. Among these products one may find powerful toxins, compounds with antitumor and anti-inflammatory activity or antibiotics. Very little is known about their role in the host organisms. However, the broad spectrum of the observed biological activity could be taken as at least circumstantial evidence to indicate the existence of some function mediated by these products and essential to their producers. 

Oligomerization of isoprenoids under elimination of pyrophosphate affords the precursors for the biosynthesis of monoterpenes, sesquiterpenes, diterpenes, triterpenes, and tetra-terpenes (93). Long-chain oligomer pyrophosphates also supply the side chains of vitamin E (99, a-tocopherol. Fig. 11), heme a (18), chlorophyll (17, Fig. 2), and the quinone type cofactors, including vitamin K (menaquinone, 98) and coenzyme QIO (ubiquinone, 97). The quinone moieties are derived from hydroxybenzoate that is synthesized from tyrosine in animals or from chorismate in microorganisms (53, 54). 

Plant secondary metabolites are biosynthesized from rather simple building blocks supplied by primary metabolism. Two important metabolic routes in this are the shikimate pathway and the isoprenoid biosynthesis. The shikimate pathway leads to the synthesis of phenolic compounds and the aromatic amino acids phenylalanine, tyrosine and tryptophan. The isoprenoid biosjmthesis is a heavily branched pathway leading to a broad spectrum of compounds (fig. 1). From plants and microorganisms more than 37,000 isoprenoid compounds have been isolated so far [1]. 

One of the more recent applications of carbene insertion into 0-H bond of alcohols includes the synthesis of chorismic (and pseudochoris-mic) acid [81], which occupies in microorganisms and plants, a strategic position in the shikimate pathway [82] as the key branch point intermediate governing the biosynthesis of aromatic aminoacids, isoprenoid qui-nones, bacterial and plant growth regulators, and other vital compounds. 

This class of fatty acids has the general formula of R-(CH2CH-CH3CH2CH2) -CH-C = CH-COOH, where R = H. These saturated and partially unsaturated multibranched fatty acids belong to the is-oprenoid acid family, and in nature, isoprenoid acids are often found in microorganisms and plants. Phytenic acid, whose systematic name is 3,7,11,15-tetramethyl-2-hexadecenoic acid (Figure 4), is one member of this class. 

Isoprenoids are widespread in microorganisms, plants, and animals. Several thousand of these compounds are known today (Table 1). 

Naphthoquinones with a long isoprenoid side chain are formed in microorganisms (menaquinones, vitamins Kg) and in higher plants (phylloquinone, vitamin K ). Naphthoquinone derivatives with short or absent side chains as well as anthraquinones of the ahzarin type are produced by a few families of higher plants, e.g., Balsaminaceae, Juglandaceae, Rubiaceae. 

The microbial production of isoprene or isoprenoids through the MVA or MEP pathway has been reported in a variety of microorganisms. The details of the engineering strategies, especially for isoprene production, are discussed below. The preferred approach of heterologous or endogenous pathway expression is determine d by the me chanism of metabolic regulatory control, the toxicity of the intermediate metabolites, and the characteristics of the key enzymes. 

A variety of microorganisms produce hydrocarbons or their precursors. For example, bacteria, primarily Bacillus, produce isoprene (Kuzma et al. 1995). Iso-prenoid compounds are common in nature, mostly in plants, and find application in human life in the production of pharmaceuticals, flavours, fragrances and pigments (Walsh 2007). Due to interest in these applications, strains of E. coli and S. cerevisiae have been established for the overproduction of certain isoprenoids. One instance is artemisinic acid, a precursor to artemisinin and an antimalaria drug... 

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