New insights into other importantPublisher: NPG; Journal: Nature: Nature; Article Type: Biology letter DOI: 10.1038/nature06269Page 2 of 33 symbiotic functions including H 2 metabolism, CO 2 -reductive acetogenesis and N 2 fixation are also provided by this first system-wide gene analysis of a microbial community specialized towards plant lignocellulose degradation. Our results underscore how complex even a 1-μl environment can be.All known termite species form obligate, nutritional mutualisms with diverse gut microbial species found nowhere else in nature 3 . Despite nearly a century of study, however, science still has only a meagre understanding of the exact roles of the host and symbiotic microbiota in the complex processes of lignocellulose degradation and conversion. Especially conspicuous is our poor understanding of the hindgut communities of wood-feeding 'higher'termites, the most species-rich and abundant of all termite lineages 4 . Higher termites do not contain hindgut flagellate protozoa, which have long been known to be sources of cellulases and hemicellulases in the 'lower' termites. The host tissue of all wood-feeding termites is known to be the source of one cellulase, a single-domain glycohydrolase family 9 enzyme that is secreted and active in the anterior compartments of the gut tract 5 . Only in recent years has research provided support for a role of termite gut bacteria in the production of relevant hydrolytic enzymes. That evidence includes the observed tight attachment of bacteria to wood particles, the antibacterial sensitivity of particle-bound cellulase activity 2 , and the discovery of a gene encoding a novel endoxylanase (glycohydrolase family 11) from bacterial DNA harvested from the gut tract of a Nasutitermes species 6 . Here, in an effort to learn about gene-centred details relevant to the diverse roles of bacterial symbionts in these successful wood-degrading insects,we initiated a metagenomic analysis of a wood-feeding 'higher' termite hindgut community, performed a proteomic analysis with clarified gut fluid from the same sample, and examined a set of candidate enzymes identified during the course of the study for demonstrable cellulase activity.A nest of an arboreal species closely related to Nasutitermes ephratae and N. corniger ( Supplementary Fig. 1) was collected near Guápiles, Costa Rica. From worker specimens, luminal contents were sampled specifically from the largest hindgut compartment, the microbedense, microlitre-sized region alternatively known as the paunch or the third proctodeal segment (P3; Fig. 1a). In the interest of interpretive clarity, we specifically excluded sampling from and analysis of the microbiota attached to the P3 epithelium and the other distinct microbial communities associated with the other hindgut compartments.Publisher: NPG; Journal: Nature: Nature; Article Type: Biology letter DOI: 10.1038/nature06269Page 3 of 33Total community DNA from pooled P3 luminal contents was purified, cloned and sequenced. About 71 million base pairs of Sang...

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In the liver 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase is present not only in the endoplasmic reticulum but also in the peroxisomes. However, to date no information is available regarding the function of the peroxisomal HMG-CoA reductase in cholesterol/isoprenoid metabolism, and the structure of the peroxisomal HMG-CoA reductase has yet to be determined. We have identified a mammalian cell line that expresses only one HMG-CoA reductase protein and that is localized exclusively to peroxisomes. This cell line was obtained by growing UT2 cells (which lack the endoplasmic reticulum HMG-CoA reductase) in the absence of mevalonate. The cells exhibited a marked increase in a 90-kDa HMG-CoA reductase that was localized exclusively to peroxisomes. The wild type Chinese hamster ovary cells contain two HMG-CoA reductase proteins, the well characterized 97-kDa protein, localized in the endoplasmic reticulum, and a 90-kDa protein localized in peroxisomes. The UT2 cells grown in the absence of mevalonate containing the up-regulated peroxisomal HMG-CoA reductase are designated UT2*. A detailed characterization and analysis of this cell line is presented in this study.In mammalian cells, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) 1 reductase is the rate-limiting enzyme for the synthesis of mevalonic acid, the precursor of cholesterol and other non-sterol isoprenoids. We and others (1-4) have demonstrated that HMG-CoA reductase is localized in two distinct intracellular compartments, endoplasmic reticulum (ER) and peroxisomes. ER HMG-CoA reductase is a 97-kDa transmembrane glycoprotein. A short non-conserved sequence links the multiple transmembrane domain to the highly conserved catalytic domain, which extends out into the cytosol. Because of its role in cholesterol biosynthesis, the regulation of HMG-CoA reductase has been intensely studied. The levels of the ER enzyme are regulated by transcription (5-7), translation (8, 9), and enzyme degradation (10, 11). Another critical role for this enzyme has emerged in recent years, due to the requirement of farnesyl diphosphate and geranyl-geranyl diphosphate in isoprenylation of proteins (12). Keller et al. (1) were the first to demonstrate that in the liver HMG-CoA reductase is present not only in the ER but also within the peroxisomes. The function of the peroxisomal reductase in cholesterol/isoprenoid metabolism has yet to be defined. However, it is clear that the ER and peroxisomal HMG-CoA reductases can be regulated differently and, therefore, may play different functional roles (2, 13). The ER reductase has a diurnal cycle distinct from that of the peroxisomal reductase (13). However, the two reductases can also be regulated coordinately. Both reductase activities are induced by cholestyramine (a bile acid resin) (2). No information is available regarding the function of the peroxisomal reductase in cholesterol/ isoprenoid metabolism, nor has the structure of the peroxisomal HMG-CoA reductase been determined. Accordingly, to facilitate our studies of the f...

We have previously identified a CHO cell line (UT2 cells) that expresses only one 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase protein which is localized exclusively in peroxisomes [Engfelt, H.W., Shackelford, J.E., Aboushadi, N., Jessani, N., Masuda, K., Paton, V.G., Keller, G.A., and Krisans, S.K. (1997) J. Biol. Chem. 272, 24579-24587]. In this study, we utilized the UT2 cells to determine the properties of the peroxisomal reductase independent of the endoplasmic reticulum (ER) HMG-CoA reductase. We demonstrated major differences between the two proteins. The peroxisomal reductase is not the rate-limiting enzyme for cholesterol biosynthesis in UT2 cells. The peroxisomal reductase protein is not phosphorylated, and its activity is not altered in the presence of inhibitors of cellular phosphatases. Its rate of degradation is not accelerated in response to mevalonate. Finally, the degradation process is not blocked by N-acetyl-Leu-Leu-norleucinal (ALLN). Furthermore, the peroxisomal HMG-CoA reductase is significantly more resistant to inhibition by statins. Taken together, the data support the conclusion that the peroxisomal reductase is functionally and structurally different from the ER HMG-CoA reductase.

Our group and others have recently demonstrated that peroxisomes contain a number of enzymes involved in cholesterol biosynthesis that previously were considered to be cytosolic or located in the endoplasmic reticulum (ER). Peroxisomes have been shown to contain HMG-CoA reductase, mevalonate kinase, phosphomevalonate kinase, phosphomevalonate decarboxylase, isopentenyl diphosphate isomerase, and FPP synthase. Four of the five enzymes required for the conversion of mevalonate to FPP contain a conserved putative PTS1 or PTS2, supporting the concept of targeted transport into peroxisomes. To date, no information is available regarding the function of the peroxisomal HMG-CoA reductase in cholesterol/isoprenoid metabolism, and the structure of the peroxisomal HMG-CoA reductase has yet to be determined. We have identified a mammalian cell line that expresses only one HMG-CoA reductase protein, and which is localized exclusively to peroxisomes, to facilitate our studies on the function, regulation, and structure of the peroxisomal HMG-CoA reductase. This cell line was obtained by growing UT2 cells (which lack the ER HMG-CoA reductase) in the absence of mevalonate. The surviving cells exhibited a marked increase in a 90-kD HMG-CoA reductase that was localized exclusively to peroxisomes. The wild-type CHO cells contain two HMG-CoA reductase proteins, the well-characterized 97-kD protein localized in the ER, and a 90-kD protein localized in peroxisomes. We have also identified the mutations in the UT2 cells responsible for the lack of the 97-kD protein. In addition, peroxisomal-deficient Pex2 CHO cell mutants display reduced HMG-CoA reductase levels and have reduced rates of sterol and nonsterol biosynthesis. These data further support the proposal that peroxisomes play an essential role in isoprenoid biosynthesis.