Bisphosphonate esters interact with HMG-CoA reductase membrane domain to induce its degradation

In all eukaryotic cells that have been examined, specific membrane arrays are induced in response to increased levels of the ER membrane protein, HMG-CoA reductase. Analysis of these inducible membranes has the potential to reveal basic insights into general membrane assembly. Yeast express two HMG-CoA reductase isozymes, and each isozyme induces a morphologically distinct proliferation of the endoplasmic reticulum. The isozyme encoded by HMG1 induces karmellae, which are long stacks of membranes that partially enclose the nucleus. In contrast, the isozyme encoded by HMG2 induces short stacks of membrane that may be associated with the nucleus, but are frequently present at the cell periphery. To understand the molecular nature of the different cellular responses to Hmg1p and Hmg2p, we mapped the region of Hmg1p that is needed for karmellae assembly. For this analysis, a series of exchange alleles was examined in which a portion of the Hmg2p membrane domain was replaced with the corresponding Hmg1p sequences. Results of this analysis indicated that the ER lumenal loop between predicted transmembrane domains 6 and 7 was both necessary and sufficient for karmellae assembly, when present in the context of an HMG-CoA reductase membrane domain. Immunoblotting experiments ruled out the simple possibility that differences in the amounts of the various chimeric HMG-CoA reductase proteins was responsible for the altered cellular responses. Our results are consistent with the hypothesis that each yeast isozyme induces or organizes a qualitatively different organization of ER membrane.

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Mutation in the Lumenal Part of the Membrane Domain of HMG-CoA Reductase Alters Its Regulated Degradation

Biochemical and Biophysical Research Communications ◽

10.1006/bbrc.1995.1026 ◽

1995 ◽

Vol 206 (1) ◽

pp. 186-193 ◽

Cited By ~ 6

Author(s):

M.S. Sekler ◽

R.D. Simoni

Keyword(s):

Membrane Domain ◽

Hmg Coa Reductase ◽

Coa Reductase

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The Role of the 3-Hydroxy 3-Methylglutaryl Coenzyme A Reductase Cytosolic Domain in Karmellae Biogenesis

Molecular Biology of the Cell ◽

10.1091/mbc.10.10.3409 ◽

1999 ◽

Vol 10 (10) ◽

pp. 3409-3423 ◽

Cited By ~ 19

Author(s):

Deborah A. Profant ◽

Christopher J. Roberts ◽

Ann J. Koning ◽

Robin L. Wright

Keyword(s):

Coenzyme A ◽

Tertiary Structure ◽

Catalytic Domain ◽

Carboxyl Terminus ◽

Membrane Domain ◽

Hmg Coa Reductase ◽

Cytosolic Domain ◽

Coa Reductase ◽

Er Membrane

In all cells examined, specific endoplasmic reticulum (ER) membrane arrays are induced in response to increased levels of the ER membrane protein 3-hydroxy 3-methylglutaryl coenzyme A (HMG-CoA) reductase. In yeast, expression of Hmg1p, one of two yeast HMG-CoA reductase isozymes, induces assembly of nuclear-associated ER stacks called karmellae. Understanding the features of HMG-CoA reductase that signal karmellae biogenesis would provide useful insights into the regulation of membrane biogenesis. The HMG-CoA reductase protein consists of two domains, a multitopic membrane domain and a cytosolic catalytic domain. Previous studies had indicated that the HMG-CoA reductase membrane domain was exclusively responsible for generation of ER membrane proliferations. Surprisingly, we discovered that this conclusion was incorrect: sequences at the carboxyl terminus of HMG-CoA reductase can profoundly affect karmellae biogenesis. Specifically, truncations of Hmg1p that removed or shortened the carboxyl terminus were unable to induce karmellae assembly. This result indicated that the membrane domain of Hmg1p was not sufficient to signal for karmellae assembly. Using β-galactosidase fusions, we demonstrated that the carboxyl terminus was unlikely to simply serve as an oligomerization domain. Our working hypothesis is that a truncated or misfolded cytosolic domain prevents proper signaling for karmellae by interfering with the required tertiary structure of the membrane domain.

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Mutations within the membrane domain of HMG-CoA reductase confer resistance to sterol-accelerated degradation

The Journal of Lipid Research ◽

10.1194/jlr.m600476-jlr200 ◽

2006 ◽

Vol 48 (2) ◽

pp. 318-327 ◽

Cited By ~ 13

Author(s):

Peter C. W. Lee ◽

Andrew D. Nguyen ◽

Russell A. DeBose-Boyd

Keyword(s):

Membrane Domain ◽

Hmg Coa Reductase ◽

Accelerated Degradation ◽

Coa Reductase

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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

The Journal of Cell Biology ◽

10.1083/jcb.117.5.959 ◽

1992 ◽

Vol 117 (5) ◽

pp. 959-973 ◽

Cited By ~ 128

Author(s):

J Roitelman ◽

EH Olender ◽

S Bar-Nun ◽

WA Dunn ◽

RD Simoni

Keyword(s):

Endoplasmic Reticulum ◽

Coenzyme A ◽

Cultured Cells ◽

Critical Role ◽

Transmembrane Helix ◽

Chimeric Protein ◽

Membrane Domain ◽

Hmg Coa Reductase ◽

Coa Reductase ◽

Peptide G

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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Loose Morphology and High Dynamism of OSER Structures Induced by the Membrane Domain of HMG-CoA Reductase

International Journal of Molecular Sciences ◽

10.3390/ijms22179132 ◽

2021 ◽

Vol 22 (17) ◽

pp. 9132

Author(s):

Ricardo Enrique Grados-Torrez ◽

Carmen López-Iglesias ◽

Joan Carles Ferrer ◽

Narciso Campos

Keyword(s):

Endoplasmic Reticulum ◽

Smooth Endoplasmic Reticulum ◽

Eukaryotic Cell ◽

Membrane Association ◽

Membrane Domain ◽

Active Components ◽

Hmg Coa Reductase ◽

Intracellular Movement ◽

Coa Reductase ◽

Confocal And Electron Microscopy

The membrane domain of eukaryotic HMG-CoA reductase (HMGR) has the conserved capacity to induce endoplasmic reticulum (ER) proliferation and membrane association into Organized Smooth Endoplasmic Reticulum (OSER) structures. These formations develop in response to overexpression of particular proteins, but also occur naturally in cells of the three eukaryotic kingdoms. Here, we characterize OSER structures induced by the membrane domain of Arabidopsis HMGR (1S domain). Immunochemical confocal and electron microscopy studies demonstrate that the 1S:GFP chimera co-localizes with high levels of endogenous HMGR in several ER compartments, such as the ER network, the nuclear envelope, the outer and internal membranes of HMGR vesicles and the OSER structures, which we name ER-HMGR domains. After high-pressure freezing, ER-HMGR domains show typical crystalloid, whorled and lamellar ultrastructural patterns, but with wide heterogeneous luminal spaces, indicating that the native OSER is looser and more flexible than previously reported. The formation of ER-HMGR domains is reversible. OSER structures grow by incorporation of ER membranes on their periphery and progressive compaction to the inside. The ER-HMGR domains are highly dynamic in their formation versus their disassembly, their variable spherical-ovoid shape, their fluctuating borders and their rapid intracellular movement, indicating that they are not mere ER membrane aggregates, but active components of the eukaryotic cell.

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