Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have raised two monospecific antibodies against synthetic peptides derived from the membrane domain of the ER glycoprotein 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, the rate limiting enzyme in the cholesterol biosynthetic pathway. This domain, which was proposed to span the ER membrane seven times (Liscum, L., J. Finer-Moore, R. M. Stroud, K. L. Luskey, M. S. Brown, and J. L. Goldstein. 1985. J. Biol. Chem. 260:522-538), plays a critical role in the regulated degradation of the enzyme in the ER in response to sterols. The antibodies stain the ER of cells and immunoprecipitate HMG-CoA reductase and HMGal, a chimeric protein composed of the membrane domain of the reductase fused to Escherichia coli beta-galactosidase, the degradation of which is also accelerated by sterols. We show that the sequence Arg224 through Leu242 of HMG-CoA reductase (peptide G) faces the cytoplasm both in cultured cells and in rat liver, whereas the sequence Thr284 through Glu302 (peptide H) faces the lumen of the ER. This indicates that a sequence between peptide G and peptide H spans the membrane of the ER. Moreover, by epitope tagging with peptide H, we show that the loop segment connecting membrane spans 3 and 4 is sequestered in the lumen of the ER. These results demonstrate that the membrane domain of HMG-CoA reductase spans the ER eight times and are inconsistent with the seven membrane spans topological model. The approximate boundaries of the proposed additional transmembrane segment are between Lys248 and Asp276. Replacement of this 7th span in HMGal with the first transmembrane helix of bacteriorhodopsin abolishes the sterol-enhanced degradation of the protein, indicating its role in the regulated turnover of HMG-CoA reductase within the endoplasmic reticulum.
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PMID:Immunological evidence for eight spans in the membrane domain of 3-hydroxy-3-methylglutaryl coenzyme A reductase: implications for enzyme degradation in the endoplasmic reticulum. 137 17

Farnesyl acetate and ethyl farnesyl ether, two analogues of farnesyl pyrophosphate, stimulate post-transcriptional down-regulation of 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase, the rate-limiting enzyme in the biosynthesis of cholesterol and isoprenoids. Farnesyl acetate and ethyl farnesyl ether reduce translation of HMG-CoA reductase mRNA and enhance degradation of the enzyme, the same regulatory effects attributed to the putative non-sterol regulatory metabolite (Goldstein, J.L., and Brown, M.S. (1990) Nature 343, 425-430). HMGal, a fusion protein consisting of the membrane domain of HMG-CoA reductase linked to Escherichia coli beta-galactosidase, is subject to the same regulated degradation as HMG-CoA reductase (Skalnik, D. G., Narita, H., Kent, C., and Simoni, R. D. (1988) J. Biol. Chem. 263, 6836-6841). At 10 micrograms/ml (37.8 microM), farnesyl acetate and ethyl farnesyl ether trigger a 50-80% reduction in HMGal activity. Farnesyl acetate reduces the synthesis of HMG-CoA reductase and HM-Gal by 60-80%, but neither farnesyl compound affects HMG-CoA reductase mRNA levels. Farnesyl acetate and ethyl farnesyl ether stimulated the degradation of HMG-CoA reductase and HMGal, reducing the half-lives of the enzymes by 40-70%. In addition to their regulatory effects on HMG-CoA reductase, these farnesyl compounds also directly disrupt sterol synthesis.
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PMID:Non-sterol compounds that regulate cholesterogenesis. Analogues of farnesyl pyrophosphate reduce 3-hydroxy-3-methylglutaryl-coenzyme A reductase levels. 812 18