3-Hydroxy-3-methylglutaryl-coenzyme A reductase from Arabidopsis thaliana is structurally distinct from the yeast and animal enzymes.

Abstract

We (1) provides a sensitive control mechanism that responds to the levels of serum cholesterol and coordinates isoprenoid metabolism to ensure the availability of both sterol and nonsterol products. The plant isoprenoid biosynthetic pathway has numerous additional branches that give rise to a number of unique products, including growth regulators (such as cytokinin, gibberellin, and abscisic acid), photosynthetic pigments, phytotoxins, phytoalexins, and a variety of specialized terpenoids. The regulated synthesis of these isoprenoid compounds is essential to plant growth and development. Studies of HMG-CoA reductase regulation in plants suggest that the enzyme activity responds to a variety of external stimuli, including light (2-4), plant growth regulators (3, 5, 6), sterols (5), and wounding and plant pathogens (7,8). Furthermore, the levels of HMG-CoA reductase activity vary markedly at different stages of development and in different plant tissues (9). Whereas the mammalian and yeast enzymes appear to be localized in the cytoplasm (10, 12), plant HMG-CoA reductase has been found in mitochondria and plastids as well as the microsomal fractions in some, but not all, species (2-8, 13). These studies raise the possibility that independent isoprenoid pathways operate in each of the compartments (14). However, the membrane association of the protein makes these determinations difficult; thus, the studies of plant HMG (20) with modifications. Single-stranded DNA was prepared as described (18) Abbreviations: HMG-CoA, 3-hydroxy-3-methylglutaryl-coenzyme A; MVA, mevalonic acid. 2779The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely to indicate this fact.

Isolation and Characterization of cDNAs Encoding Wheat 3-Hydroxy-3-Methylglutaryl Coenzyme A Reductase

“…Occasionally, we observed a smaller transcript of about 2.4 kb in leaf tissues that is less abundant (about one-tenth) than the 3.0-kb mRNA. The sizes of the mRNA are similar to those reported in tomato (Narita and Gruissem, 1989) and Arabidopsis (Caelles et al, 1989;Learned and Fink, 1989). These transcripts may represent different forms of the enzyme present in different subcellular compartments.…”

“…The first section at the base of the leaf is the youngest, and the tip section is the oldest (Fig. 8) (Caelles et al, 1989;Learned and Fink, 1989), tomato (Narita and Gruissem, 1989), human (Luskey and Stevens, 1985), yeast (Basson et al, 1988), and Drosophila (Gertler et al, 1988). Relative to the wheat sequence, identical or conserved residues are shown in gray and residues that are neither identical nor conserved are shown in white.…”

“…The degree of sequence homology among the three cDNAs is very high, as indicated by the shading. Figure 3 shows sequence homology comparison among HMGR genes by computer alignment of the translated wheat HMGR 18 partial cDNA sequence with that from Arabidopsis (Caelles et al, 1989;Learned and Fink, 1989), tomato (Narita and Gruissem, 1989;Narita et al, 1991), human (Luskey and Stevens, 1985), yeast (Basson et al, 1988), and Drosophila (Gertler et al, 1988).…”

Cloning and Characterization of a Gene Encoding HMG-CoA Reductase fromGanoderma lucidumand Its Functional Identification in Yeast

“…[14][15][16][17] In contrast, the membrane domains of plant HMGR proteins have only one or two transmembrane segments. [18][19][20] The N-terminal membranebound domain, although not necessary for catalytic activity, is required for sterol-regulated degradation of the protein 17) and for membrane proliferation. 21) Hence, HMGR activity does not require association with the N-terminal hydrophobic domain.…”

“…19) In view of a possible quantitative correlation between HMGR expression levels and triterpene production, it is of interest to study the HMGR-catalyzed committed step at the molecular level.…”