Control of Sterol Biosynthesis and its Importance to Developmental Regulation and Evolution

Nes, W. David

doi:10.1007/978-1-4684-8789-3_9

Cited by 18 publications

(16 citation statements)

References 86 publications

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“…Indeed, the increase in the levels of steryl esters accounted for the majority of the increase in total sterols observed during seed development. These results contrast sharply with those obtained in studies measuring sterol accumulation in plant vegetative tissue (Nes 1990). In rape, the accumulation of steryl esters also accounts for a significant proportion of the total sterols accumulated during seed development (Fig.…”

Section: Phytosterol Accumulation In Developing Oilseedscontrasting

confidence: 95%

Co-ordinate regulation of sterol biosynthesis enzyme activity during accumulation of sterols in developing rape and tobacco seed

Harker

Hellyer

Clayton

et al. 2003

Planta

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The activities of 3-hydroxy-3-methylglutarylcoenzyme A reductase, sterol methyl transferase 1 and sterol acyltransferase, key enzymes involved in phytosterol biosynthesis were shown to be co-ordinately regulated during oilseed rape (Brassica napus L.) and tobacco (Nicotiana tabacum L.) seed development. In both plants, enzyme activities were low during the initial stages of seed development, increasing towards midmaturation where they remained stable for a time, before declining rapidly as the oilseeds reached maturity. During seed development, the level of total sterols increased 12-fold in tobacco and 9-fold in rape, primarily due to an increase in steryl ester production. In both seed tissues, stages of maximum enzyme activity coincided with periods of high rates of sterol production, indicating developmental regulation of the enzymes to be responsible for the increases in the sterol content observed during seed development. Consistent with previous studies the data presented suggest that sterol biosynthesis is regulated by two key steps, although there may be others. The first is the regulation of carbon flux into the isoprenoid pathway to cycloartenol. The second is the flux from cycloartenol to D 5 -end-product sterols. The implications of the results in terms of enhancing seed sterol levels by genetic modification are also discussed.

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Section: Phytosterol Accumulation In Developing Oilseedscontrasting

confidence: 95%

Co-ordinate regulation of sterol biosynthesis enzyme activity during accumulation of sterols in developing rape and tobacco seed

Harker

Hellyer

Clayton

et al. 2003

Planta

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“…many as 60 sterols in a single organism [16,17]. The type and amount of sterol that accumulates in cells may change during development [1], suggesting different levels of sterol homoeostasis as affected by regulation of the SMT activity via modulators such as ATP or transcript expression [18] and/or by compartmentation and trafficking [19]. Many of these compounds are minor intermediates, while others that are 5 -sterols at trace levels might play non-metabolic roles such as signal molecules [20][21][22].…”

Section: Scheme 1 Cycloartenol-lanosterol Bifurcation To Phytosterolsmentioning

confidence: 99%

“…In eukaryotes, evolution of the phytosterol pathway is operated by selection of greasy substrates that will fit the active sites of at least nine enzymes, not necessarily structurally similar but nevertheless microsomally organized in the cell, to produce 24-alkyl sterol membrane inserts [1,2]. The initial processing of tetracyclic sterols with a 24 -bond generated by the cyclization of squalene oxide usually involves SMT (sterol methyltransferase) participation.…”

Section: Introductionmentioning

confidence: 99%

Enzyme redesign and interactions of substrate analogues with sterol methyltransferase to understand phytosterol diversity, reaction mechanism and the nature of the active site

Nes

2005

Biochemical Society Transactions

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Several STM (sterol methyltransferase) genes have been cloned, sequenced and expressed in bacteria recently, making it possible to address questions of the relationship between sterol structure and function. The active site and mechanism of action of a set of phylogenetically diverse SMTs have been probed by site-directed mutagenesis as well as by using substrate and related analogues of the SMT-catalysed reaction. An active-site model has been developed that is in accord with the results presented, which is consistent with the hypothesis that SMTs are bifunctional enzymes kinetically responsible to bind 24 -acceptor sterols of specific steric and electronic character and rigid orientation imposed by multiple hydrophobic active site contacts exacted from a common waxy core. Functional divergence influenced by the architectural role of sterols in membranes is considered to govern the evolution of product distribution and specificity of individual SMTs as discussed.

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“…Lanosterol synthase belongs to the large family of OSCs (oxidosqualene cyclases), eukaryotic enzymes that catalyse the cyclization of 2,3-oxidosqualene into different cyclic compounds: lanosterol alone in non-photosynthetic organisms (fungi and mammals), cycloartenol, precursor of phytosterols and other tetra-and pentacyclic compounds in plants [1].…”

mentioning

confidence: 99%

Access of the substrate to the active site of squalene and oxidosqualene cyclases: comparative inhibition, site-directed mutagenesis and homology-modelling studies

Oliaro‐Bosso

Schulz‐Gasch

Taramino

et al. 2005

Biochemical Society Transactions

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Substrate access to the active-site cavity of squalene-hopene cyclase from Alicyclobacillus acidocaldarious and lanosterol synthase [OSC (oxidosqualene cyclase)] from Saccharomyces cerevisiae was studied by an inhibition, mutagenesis and homology-modelling approach. Crystal structure and homology modelling indicate that both enzymes possess a narrow constriction that separates an entrance lipophilic channel from the active-site cavity. The role of the constriction as a mobile gate that permits substrate passage was investigated by experiments in which critically located Cys residues, either present in native protein or inserted by site-directed mutagenesis, were labelled with specifically designed thiol-reacting molecules. Some amino acid residues of the yeast enzyme, selected on the basis of sequence alignment and a homology model, were individually replaced by residues bearing side chains of different lengths, charges or hydrophobicities. In some of these mutants, substitution severely reduced enzymatic activity and thermal stability. Homology modelling revealed that in these mutants some critical stabilizing interactions could no longer occur. The possible critical role of entrance channel and constriction in specific substrate recognition by eukaryotic OSC is discussed.In cholesterol and ergosterol biosynthesis, the most significant structural alteration occurring along the pathway, that is generation of the steroid nucleus after assembly of the triterpene backbone, is brought about by lanosterol synthase. Lanosterol synthase belongs to the large family of OSCs (oxidosqualene cyclases), eukaryotic enzymes that catalyse the cyclization of 2,3-oxidosqualene into different cyclic compounds: lanosterol alone in non-photosynthetic organisms (fungi and mammals), cycloartenol, precursor of phytosterols and other tetra-and pentacyclic compounds in plants [1].Prokaryotes possess an enzyme similar to OSCs: SHC (squalene-hopene cyclase) that converts squalene into hopene or diplopterol, pentacyclic precursors of hopanoids [2]. Interestingly, while all the known OSCs only accept 2,3-oxidosqualene as substrate, SHC not only accepts its physiological substrate squalene, but also the eukaryotes' substrate, 2,3-oxidosqualene [3].Squalene and OSCs catalyse among the most fascinating and complex monoenzymatic reactions (Figure 1). During the process, which is primed by protonation of the substrate, four or five rings are formed, several chiral centres are created, hydride and methyl groups are 1,2 shifted and a proton is

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Control of Sterol Biosynthesis and its Importance to Developmental Regulation and Evolution

Cited by 18 publications

References 86 publications

Co-ordinate regulation of sterol biosynthesis enzyme activity during accumulation of sterols in developing rape and tobacco seed

Co-ordinate regulation of sterol biosynthesis enzyme activity during accumulation of sterols in developing rape and tobacco seed

Enzyme redesign and interactions of substrate analogues with sterol methyltransferase to understand phytosterol diversity, reaction mechanism and the nature of the active site

Access of the substrate to the active site of squalene and oxidosqualene cyclases: comparative inhibition, site-directed mutagenesis and homology-modelling studies

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