Isolation and characterization of a cDNA encoding a 3-hydroxy-3-methylglutaryl coenzyme A reductase from Nicotiana sylvestris

A cDNA library from freshly isolated mesophyll protoplasts of Nicotiana sylvestris was differentially screened using cDNAs from leaves, leaf strips submitted to the same stress as protoplasts during the isolation procedure, and cell suspension cultures. One of the selected clones (6P2) was found to encode a putative polypeptide highly homologous to previously characterized 3-hydroxy-3-methylglutaryl coenzyme A reductases. The C-terminal region of the polypeptide was highly conserved whereas its N-terminal region including the trans-membrane domains and the linker was more variable. Apart from protoplasts, the 6P2 gene was found to be expressed in apexes, anthers, roots, and in stressed leaf strips after 24h of culture, during the hypersensitive reaction to viral infection and after HgCl₂ treatment. This pattern of expression is consistent with a role in plant defence mechanisms.     

Expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in maize tissues

The activity of the enzyme 3-hydroxy-3-methlglutaryl-coenzyme A reductase (HMGR, EC 1.1.1.34) is highly expressed in 4-day-old etiolated seedlings of normal (cv. DeKalb XL72AA), dwarf ( d ₅) and albino ( lw ₃) maize ( Zea mays L.). HMGR activity of maize seedlings appeared to be exclusively associated with the microsomal rather than the plastidic fraction of maize cells. Maize tissues with high meristematic activity such as germinating seeds, leaf bases, root tips and the site of origin of lateral roots contained high levels of microsomal HMGR activity. The activity of HMGR extracted from leaf tips of normal, dwarf and albino maize seedlings is regulated by light. Microsomal HMGR activity from leaf tips of 4-day-old maize seedlings was inhibited significantly following exposure to strong light (600 μmol m⁻² s⁻¹) for more than 10 h. By comparison, microsomal HMGR activity from leaf bases and root tips of maize was not inhibited by exposure to strong light. These results suggest that the microsomal HMGR which is highly expressed in maize may be related to sterol biosynthesis and membrane biogenesis rather than plastidic-associated isoprenoid synthesis and that light may regulate HMGR activity indirectly by increasing cell differentiation.     

Multiple phosphorylation of rat liver 3-hydroxy 3-methylglutaryl coenzyme a reductase

Rat liver homogeneous ³²P-labeled hydroxy methylglutaryl coenzyme A reductase, was treated independently with CNBr and trypsin and the resulting [³²P]phosphopeptides were analyzed by disc gel electrophoresis. CNBr treatment produced only one ³²P-fragment of Mr 18,000. The time course of trypsin hydrolysis initially showed the appearance of some phosphopeptides, which were lately converted in two phosphopeptides of low Mr. These results provide direct support for the concept that hydroxy methyl glutaryl coenzyme A reductase kinase solubilized from microsomes phosphorylates only two sites or set of sites in the reductase molecule.     

细纹豆芫菁3-羟甲基戊二酰辅酶A-还原酶基因全长cDNA克隆及生物信息学分析

3-羟甲基戊二酰辅酶A-还原酶（3-hydroxy-3-methylglutaryl coenzyme A reductase, HMGR）是甲羟戊酸途径的关键酶。获得芫菁体内HMGR基因信息是确定甲羟戊酸途径与斑蝥素合成相关性的基础。本研究利用RACE技术从细纹豆芫菁Epicauta mannerheimi (Maklin)体内克隆获得HMGR基因全长cDNA序列, 命名为EmHMGR（GenBank登录号为JQ690539）。该基因全长3 118 bp, 其中5′端非翻译区178 bp, 3′端非翻译区414 bp, 开放阅读框2 526 bp, 编码842个氨基酸。推测的蛋白质分子量为92.8 kDa, 理论等电点为6.0, 预测分子式为C₄₁₃₅H₆₆₀₄N1₀₉₈O₁₂₁₆S₅₀, 不稳定系数为43.37, 总亲水性系数为0.091, 为疏水性不稳定蛋白。序列分析发现该基因编码的蛋白与已报道的其他昆虫HMGR的氨基酸序列一致性达50%以上, 而且包含HMGR_Class I保守功能域、 固醇敏感多肽区及HMGR蛋白的其他保守功能位点。系统进化分析发现该基因与叶甲科昆虫HMGR基因的关系最近。本研究首次从芫菁科昆虫体内克隆获得甲羟戊酸途径的关键酶EmHMGR基因, 为后期芫菁体内斑蝥素生物合成途径的研究奠定了基础。     

Phosphorylation of 3-hydroxy-3-methylglutaryl coenzyme A reductase by microsomal 3-hydroxy-3-methylglutaryl coenzyme A reductase kinase

Microsomal 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase kinase has been purified to apparent homogeneity by a process involving the following steps: solubilization from microsomes and chromatography on Affi-Gel Blue, phosphocellulose, Bio-Gel A 1.5m, and agarose-hexane-ATP. The apparent M_r of the purified enzyme as judged by gel-filtration chromatography is 205,000 and by sodium dodecyl sulfate-gel electrophoresis is 105,000. Immunoprecipitation of homogeneous reductase phosphorylated by reductase kinase and [γ-³²P]ATP produces a unique band containing ³²P bound to protein which migrates at the same R_f as the reductase subunit. Incubation of ³²P-labeled HMG-CoA reductase with reductase phosphatase results in a time-dependent loss of protein-bound ³²P radioactivity, as well as an increase in enzymic activity. Reductase kinase, when incubated with ATP, undergoes autophosphorylation, and a simultaneous increase in its enzymatic activity is observed. Tryptic treatment of immunoprecipitated, ³²P-labeled HMG-CoA reductase phosphorylated with reductase kinase produces only one ³²P-labeled phosphopeptide with the same R_f as one of the two tryptic phosphopeptides that have been reported in a previous paper. The possible existence of a second microsomal reductase kinase is discussed.     

Cellular distribution of 3-hydroxy-3-methylglutaryl coenzyme a reductase and mevalonate kinase in leaves of Nepeta cataria

In Nepeta cataria leaf tissue there are two separate activities of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase and mevalonate (MVA) kinase respectively as determined by the use of a 20–45% discontinuous sucrose density gradient. Cell-free extracts of leaf and callus tissue were prepared and HMG-CoA reductase and MVA kinase activities were compared to activities in extracts from porcine livers and yeast autolysates. Callus tissue from N. cataria has only one peak of HMG-CoA reductase and MVA kinase activity located at the top of the sucrose density gradient. Isolated chloroplast from N. cataria leaves have one peak of HMG-CoA reductase and MVA kinase activity, located near the bottom of a sucrose density gradient. MVA kinase activities in porcine livers and yeast autolysate also showed only one activity profile, located at the top of the sucrose gradient. Partial purification of the leaf extract through the use of differential centrifugation, 30–70% ammonium sulfate precipitation and Bio-Gel P-100 column chromatography shows that MVA kinase, 5-phosphomevalonate (MVAP) kinase and 5-pyrophosphomevalonate (MVAPP) decarboxylase activities remain in the same fractions. The extra-chloroplastidic HMG-CoA reductase activity may be separated from MVA kinase activity by differential centrifugation. These results suggest the presence of two HMG-CoA reductase and MVA kinase enzymes in N. cataria leaf tissue—one located in the chloroplast and a second being extra-chloroplastidic.     

Human hepatic 3-hydroxy-3-methylglutaryl coenzyme A reductase: evidence for the regulation of enzymic activity by a bicyclic phosphorylation cascade

Microsomal human liver HMG-CoA reductase has been shown to exist in active (dephosphorylated) and inactive (phosphorylated) forms. Microsomal HMG-CoA reductase was inactivated in vitro by ATP-Mg in a time dependent manner; this inactivation was mediated by reductase kinase. Incubation of inactivated enzyme with phosphatase resulted in a time dependent reactivation (dephosphorylation). Polyacrylamide gel electrophoresis of purified HMG-CoA reductase incubated with reductase kinase and radiolabeled ATP revealed that the 32P radioactivity and HMG-CoA reductase enzymic activity were localized in a single electrophoretic position. Partial dephosphorylation of the phosphorylated enzyme was associated with loss of 32P and increase in HMG-CoA reductase activity. Human reductase kinase also exists in active and inactive forms. The active (phosphorylated) form of reductase kinase can be inactivated by incubation with phosphatase. Phosphorylation of inactive reductase kinase with ATP-Mg and a second kinase, reductase kinase kinase, was associated with a parallel increase in the enzymic activity of reductase kinase and the ability to inactivate HMG-CoA reductase. The combined results present initial evidence for the presence of human HMG-CoA reductase and reductase kinase in active and inactive forms, and the in vitro modulation of its enzymic activity by a bicyclic phosphorylation cascade. This bicyclic cascade system may provide a mechanism for short-term regulation of the pathway for cholesterol biosynthesis in man.     

Proteinase involvement in the solubilization of 3-hydroxy-3-methylglutaryl coenzyme a reductase

This paper demonstrates that a heavy particle fraction, which contains lysosomes, is required for the solubilization of HMG-CoA reductase from rat liver microsomes by the widely-used slow freeze-thaw procedure. This solubilization is effectively inhibited by the proteinase inhibitors, leupeptin and antipain, but not by phenylmethylsulfonyl fluoride, pepstatin A or N-α-p-tosyl-L-lysine methyl ester. These results suggest that a thiol proteinase, possibly derived from lysosomes, is responsible for solubilizing the reductase.     

Isolation of a monocot 3-hydroxy-3-methylglutaryl coenzyme A reductase gene that is elicitor-inducible

The rice (Oryza sativa) phytoalexins, momilactones and oryzalexins, are synthesized by the isoprenoid pathway. An early step in this pathway, one that is rate-limiting in mammalian systems, is catalyzed by the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR). A gene that encodes this enzyme has been isolated from rice, and found to contain an open reading frame of 1527 bases. The encoded protein sequence of the rice HMGR appears to be conserved with respect to other HMGR proteins, and 1 or 2 membrane-spanning domains characteristic of plant HMGRs are predicted by a hydropathy plot of the amino acid sequence. The protein is truncated at its 5 end, and shows reduced sequence conservation in this region as compared to other plant sequences. The rice genome contains a small family of HMGR genes. The isolated gene, HMGR I, is expressed at low levels in both vegetative and floral organs of rice plants. It is not induced in plants by wounding, but is strongly and rapidly induced in suspension cells by a fungal cell wall elicitor from the pathogenMagnaporthe grisea, causal agent of rice blast disease. This suggests that HMGR I may be important in the induction of rice phytoalexin biosynthesis in response to pathogen attack, and therefore may play a key role as a component of the inducible defense mechanism in rice.     

Cloning and characterization of a novel 3-hydroxy-3-methylglutaryl coenzyme A reductase gene from Salvia miltiorrhiza involved in diterpenoid tanshinone accumulation

The 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyzes the conversion of HMG-CoA to mevalonate (MVA), which is a rate-limiting step in the isoprenoid biosynthesis via the MVA pathway. In this study, the full-length cDNA encoding HMGR (designated as SmHMGR2, GenBank accession no. FJ747636) was isolated from Salvia miltiorrhiza by rapid amplification of cDNA ends (RACE). The cloned gene was then transformed into the hairy root of S. miltiorrhiza, and the enzyme activity and production of diterpenoid tanshinones and squalene were monitored. The full-length cDNA of SmHMGR2 comprises 1959 bp, with a 1653-bp open reading frame encoding a 550-amino-acid protein. Molecular modeling showed that SmHMGR2 is a new HMGR with a spatial structure similar to other plant HMGRs. SmHMGR2 contains two HMG-CoA-binding motifs and two NADP(H)-binding motifs. The SmHMGR2 catalytic domain can form a homodimer. The deduced protein has an isoelectric point of 6.28 and a calculated molecular weight of approximately 58.67 kDa. Sequence comparison analysis showed that SmHMGR2 had the highest homology to HMGR from Atractylodes lancea. As expected, a phylogenetic tree analysis indicates that SmHMGR2 belongs to plant HMGR group. Tissue expression pattern analysis shows that SmHMGR2 is strongly expressed in the leaves, stem, and roots. Functional complementation of SmHMGR2 in HMGR-deficient mutant yeast JRY2394 demonstrates that SmHMGR2 mediates the MVA biosynthesis in yeasts. Overexpression of SmHMGR2 increased enzyme activity and enhanced the production of tanshinones and squalene in cultured hairy roots of S. miltiorrhiza. Our DNA gel blot analysis has confirmed the presence and integration of the associated SmHMGR2 gene. SmHMGR2 is a novel and important enzyme involved in the biosynthesis of diterpenoid tanshinones in S. miltiorrhiza.     

Regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase

Molecular and Cellular Biochemistry - Within the last few years considerable evidence has accumulated which indicates that changes in HMG-CoA reductase are due primarily, if not solely, to changes...     

Improved assay of 3-hydroxy-3-methylglutaryl coenzyme A reductase

Two improvements are described for the assay of HMG CoA reductase. These are a simple synthesis of the substrate precursor HMG-3-(14)C anhydride and a double-label ((14)C and (3)H) method for determining the amount of mevalonate-3-(14)C that is formed from the substrate.     

Cloning and characterization of the gene encoding 3-hydroxy-3-methylglutaryl coenzyme A reductase in melon (Cucumis melo L. reticulatus)

We have isolated a cDNA for Cm-HMGR, encoding 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase in melon (Cucumis melo L. reticulatus; Genbank Accession No. AB021862). Cm-HMGR encodes a polypeptide of 588 amino acids that contains two transmembrane domains and a catalytic domain. Database searches revealed that Cm-HMGR shows homology to HMG1 (63.7%) and HMG2 (70.3%) of tomato, to HMG1 (77.2%) and HMG2 (69.4%) of Arabidopsis thaliana, and to HMGR of tobacco (72.6%). Functional expression in a HMG-CoA reductase-deficient mutant yeast showed that Cm-HMGR products mediate the synthesis of mevalonate. Northern analysis revealed that the level of Cm-HMGR mRNA in the fruit increased after pollination and markedly decreased at the end of fruit enlargement. During ripening, Cm-HMGR mRNA levels increased markedly in the fruit. In parallel with mRNA expression, Cm-HMGR activity increased after pollination, whereas no Cm-HMGR activity was detectable during fruit ripening. Our results suggest that Cm-HMGR is important during early post-pollination development of the fruit in melon.     

Isolation and characterization of cDNAs encoding wheat 3-hydroxy-3-methylglutaryl coenzyme A reductase.

The enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMGR, EC 1.1.1.34) is a key enzyme in the isoprenoid biosynthetic pathway. We have isolated partial cDNAs from wheat (Triticum aestivum) using the polymerase chain reaction. Comparison of deduced amino acid sequences of these cDNAs shows that they represent a small family of genes that share a high degree of sequence homology among themselves as well as among genes from other organisms including tomato, Arabidopsis, hamster, human, Drosophila, and yeast. Southern blot analysis reveals the presence of at least four genes. Our results concerning the tissue-specific expression as well as developmental regulation of these HMGR cDNAs highlight the important role of this enzyme in the growth and development of wheat.     

Purification of 3-hydroxy-3-methylglutaryl coenzyme A reductase from rat liver

A procedure for the purification of 3-hydroxy-3-methylglutaryl coenzyme A reductase [mevalonate:NADP⁺ oxidoreductase (CoA-acylating); EC 1.1.1.34] from rat liver microsomes has been developed. The enzyme preparations obtained by this procedure have specific activities of 16 to 23 μmol of mevalonate formed per minute per milligram of protein. These enzyme preparations were judged to be homogeneous on the basis of comigration of enzyme activity and protein on polyacrylamide gels.     

Purification of 3-hydroxy-3-methylglutaryl coenzyme A reductase.

This paper describes a rapid purification procedure for 3-hydroxy-3-methylglutaryl coenzyme A reductase, the major regulatory enzyme in hepatic cholesterol biosynthesis. A freeze-thaw technique is used for solubilizing the enzyme from rat liver microsomal membranes. No detergents or other stringent conditions are required. The purification procedure employs Blue Dextran-Sepharose-4B affinity chromatography, and purification can be carried out from microsomal membranes to purified enzyme in 8 to 10 hours. The purified enzyme has a specific activity of 517 nmoles/min/mg protein, and it is 975-fold purified with respect to the original microsomal membrane suspension. SDS polyacrylamide gel electrophoresis of the purified enzyme shows only trace impurities; the subunit molecular weight for the enzyme measured by this technique is 47,000.     

Genetic and biochemical analysis of the transmembrane domain of Arabidopsis 3-hydroxy-3-methylglutaryl coenzyme A reductase

We have examined the amino terminal membrane anchoring domain of Arabidopsis thaliana 3-hydroxy-3-methylglutaryl coenzyme A reductase (Hmg1p), a key enzyme of the isoprenoid biosynthetic pathway. Using both in vitro and in vivo approaches, we have analyzed a series of recombinant derivatives to identify key structural elements which play a role in defining Hmg1p transmembrane topology. Based on our results, we have proposed a topological model for Hmg1p in which the enzyme spans the lipid bilayer twice. We have shown the two transmembrane segments, designated TMS1 and TMS2, to be structurally and functionally inequivalent in their ability to direct the targeting and orientation of reporter proteins. Furthermore, we provide evidence indicating both the extreme amino terminal end and carboxyl terminal domain of the protein reside in the cytosol. This model therefore provides a key basis for the future examination of the role of the transmembrane domain in the targeting and regulation of Hmg1p in plant cells. J. Cell. Biochem. 65:443–459. © 1997 Wiley-Liss Inc.