ABSTRACT
The creative process in art and science involves two phases-generating and exploring new and wild ideas (building castles in the sky) and then narrowing down and focusing on the most tractable and useful ones (building houses of cards that don't topple over).
Subject(s)
Awards and Prizes , Creativity , Science , Art , HumansABSTRACT
Truly creative works of science and art produce unexpected and surprising results-just like the punch line of a good joke that generates an unfamiliar twist on a familiar idea. Surprise stimulates curiosity, which triggers a search to reveal the mystery of things unknown.
Subject(s)
Art , Creativity , Science , Wit and Humor as Topic , Awards and Prizes , Humans , Paintings , SculptureABSTRACT
The cholesterol-sensing protein Scap induces cholesterol synthesis by transporting membrane-bound transcription factors called sterol regulatory element-binding proteins (SREBPs) from the endoplasmic reticulum (ER) to the Golgi apparatus for proteolytic activation. Transport requires interaction between Scap's two ER luminal loops (L1 and L7), which flank an intramembrane sterol-sensing domain (SSD). Cholesterol inhibits Scap transport by binding to L1, which triggers Scap's binding to Insig, an ER retention protein. Here we used cryoelectron microscopy (cryo-EM) to elucidate two structures of full-length chicken Scap: (1) a wild-type free of Insigs and (2) mutant Scap bound to chicken Insig without cholesterol. Strikingly, L1 and L7 intertwine tightly to form a globular domain that acts as a luminal platform connecting the SSD to the rest of Scap. In the presence of Insig, this platform undergoes a large rotation accompanied by rearrangement of Scap's transmembrane helices. We postulate that this conformational change halts Scap transport of SREBPs and inhibits cholesterol synthesis.
Subject(s)
Cholesterol/metabolism , Membrane Proteins/chemistry , Membrane Proteins/metabolism , Amino Acid Sequence , Animals , Antibodies/metabolism , Chickens , Membrane Proteins/isolation & purification , Membrane Proteins/ultrastructure , Models, Biological , Models, Molecular , Protein Binding , Protein Domains , Protein Structure, Secondary , Structure-Activity RelationshipABSTRACT
Tragic events such as pandemics can be remembered as well as foreshadowed by works of art. Paintings by the artists Edvard Munch and John Singer Sargent (1918-19) tell us in real time what it was like to be stricken by the Spanish flu. Paintings by Edward Hopper (1940s and '50s) foretell the lockdown and social distancing of today's COVID-19 pandemic.
Subject(s)
Coronavirus Infections , Influenza Pandemic, 1918-1919 , Medicine in the Arts , Pandemics , Pneumonia, Viral , COVID-19 , Coronavirus Infections/epidemiology , Disease Outbreaks , Famous Persons , History, 20th Century , Humans , Influenza, Human/epidemiology , Pneumonia, Viral/epidemiology , World War IABSTRACT
The iconic phrase "a shot heard 'round the world" signifies an exceptional event. Seurat's masterpiece La Grande Jatte, painted with many thousand dots of color, came as a shot to the art world-a shot fired by the imagination of the artist and inspired by the color theories of a scientist.
Subject(s)
Awards and Prizes , Color Perception , Color , Creativity , Optical Illusions , Paintings/history , Chemistry , Coloring Agents/chemistry , France , History, 19th Century , History, 20th Century , Humans , PaintABSTRACT
Scap is a polytopic membrane protein that functions as a molecular machine to control the cholesterol content of membranes in mammalian cells. In the 21 years since our laboratory discovered Scap, we have learned how it binds sterol regulatory element-binding proteins (SREBPs) and transports them from the endoplasmic reticulum (ER) to the Golgi for proteolytic processing. Proteolysis releases the SREBP transcription factor domains, which enter the nucleus to promote cholesterol synthesis and uptake. When cholesterol in ER membranes exceeds a threshold, the sterol binds to Scap, triggering several conformational changes that prevent the Scap-SREBP complex from leaving the ER. As a result, SREBPs are no longer processed, cholesterol synthesis and uptake are repressed, and cholesterol homeostasis is restored. This review focuses on the four domains of Scap that undergo concerted conformational changes in response to cholesterol binding. The data provide a molecular mechanism for the control of lipids in cell membranes.
Subject(s)
Cholesterol/metabolism , Intracellular Signaling Peptides and Proteins/metabolism , Membrane Proteins/metabolism , Animals , Homeostasis , Humans , Intracellular Signaling Peptides and Proteins/chemistry , Intracellular Signaling Peptides and Proteins/genetics , Membrane Proteins/chemistry , Membrane Proteins/genetics , Models, Biological , Models, Molecular , Protein Conformation , Protein Transport , Proteolysis , Receptors, LDL/metabolism , Sterol Regulatory Element Binding Proteins/metabolismABSTRACT
Works of art and science that achieve masterpiece status share several characteristics: they convey a special type of originality that captures the imagination, they stand the test of time, and they change the way artists or scientists think about their field.
Subject(s)
Art , Creativity , Science , HumansABSTRACT
The Spanish artist Diego Velázquez created a puzzle-painting 360 years ago that to this day remains unsolved, but still mystifies and intrigues. Unlike artists who get their thrills by creating puzzles that stimulate the imagination, scientists get their kicks by solving puzzles that advance biomedical research.
Subject(s)
Awards and Prizes , Biomedical Research , Women's Health , Art/history , History, 17th Century , History, 20th Century , Science , WorkforceABSTRACT
For many scientific awards, such as Nobels and Laskers, the maximum number of recipients is three. This Rule of Three forces selection committees to make difficult decisions that increase the likelihood of singling out those individuals who open a new field and continue to lead it. The Rule of Three is reminiscent of art's three-panel triptych, a form that the modern master Francis Bacon used to distill complex stories in a bold way.
ABSTRACT
For more than a century, historians of science have been spinning a philosophical roulette wheel, pondering which is more important in the creative process: imagination or knowledge. The most original scientists (and artists) in our day discover newness by blending existing knowledge with imaginative thinking.
Subject(s)
Art , Creativity , Knowledge , Science , Animals , Art/history , Awards and Prizes , Chemistry, Physical/history , History, 20th Century , Horses/anatomy & histology , Horses/physiology , Science/historyABSTRACT
One-fourth of all deaths in industrialized countries result from coronary heart disease. A century of research has revealed the essential causative agent: cholesterol-carrying low-density lipoprotein (LDL). LDL is controlled by specific receptors (LDLRs) in liver that remove it from blood. Mutations that eliminate LDLRs raise LDL and cause heart attacks in childhood, whereas mutations that raise LDLRs reduce LDL and diminish heart attacks. If we are to eliminate coronary disease, lowering LDL should be the primary goal. Effective means to achieve this goal are currently available. The key questions are: who to treat, when to treat, and how long to treat.
Subject(s)
Cholesterol/metabolism , Coronary Vessels/pathology , Hydroxymethylglutaryl-CoA Reductase Inhibitors/therapeutic use , Plaque, Atherosclerotic/drug therapy , Animals , Cardiovascular Diseases/drug therapy , Cardiovascular Diseases/genetics , Cardiovascular Diseases/pathology , Coronary Vessels/metabolism , Dietary Fats/metabolism , Humans , Plaque, Atherosclerotic/genetics , Plaque, Atherosclerotic/metabolism , Receptors, LDL/metabolismABSTRACT
Wild-type (WT) mice maintain viable levels of blood glucose even when adipose stores are depleted by 6 d of 60% calorie restriction followed by a 23-h fast (hereafter designated as "starved" mice). Survival depends on ghrelin, an octanoylated peptide hormone. Mice that lack ghrelin suffer lethal hypoglycemia when subjected to the same starvation regimen. Ghrelin is known to stimulate secretion of growth hormone (GH), which in turn stimulates secretion of IGF-1 (insulin-like growth factor-1). In the current study, we found that starved ghrelin-deficient mice had a 90% reduction in plasma IGF-1 when compared with starved WT mice. Injection of IGF-1 in starved ghrelin-deficient mice caused a twofold increase in glucose production and raised blood glucose to levels seen in starved WT mice. Increased glucose production was accompanied by increases in plasma glycerol, fatty acids and ketone bodies, and hepatic triglycerides. All of these increases were abolished when the mice were treated with atglistatin, an inhibitor of adipose tissue triglyceride lipase. We conclude that IGF-1 stimulates adipose tissue lipolysis in starved mice and that this lipolysis supplies energy and substrates that restore hepatic gluconeogenesis. This action of IGF-1 in starved mice is in contrast to its known action in inhibiting adipose tissue lipase in fed mice. Surprisingly, the ghrelin-dependent maintenance of plasma IGF-1 in starved mice was not mediated by GH. Direct injection of GH into starved ghrelin-deficient mice failed to increase plasma IGF-1. These data call attention to an unsuspected role of IGF-1 in the adaptation to starvation.
Subject(s)
Blood Glucose , Insulin-Like Growth Factor I , Starvation , Adaptation, Physiological , Adipose Tissue/drug effects , Adipose Tissue/enzymology , Adipose Tissue/metabolism , Animals , Blood Glucose/metabolism , Fatty Acids/blood , Ghrelin/metabolism , Gluconeogenesis , Glycerol/blood , Growth Hormone/metabolism , Insulin-Like Growth Factor I/analysis , Insulin-Like Growth Factor I/metabolism , Ketone Bodies/blood , Lipase/antagonists & inhibitors , Lipase/metabolism , Lipolysis , Liver/metabolism , Mice , Phenylurea Compounds/pharmacology , Starvation/blood , Starvation/metabolism , Triglycerides/metabolismABSTRACT
Low-density lipoprotein (LDL) delivers cholesterol to mammalian cells through receptor-mediated endocytosis. The LDL cholesterol is liberated in lysosomes and transported to the plasma membrane (PM) and from there to the endoplasmic reticulum (ER). Excess ER cholesterol is esterified with a fatty acid for storage as cholesteryl esters. Recently, we showed that PM-to-ER transport of LDL cholesterol requires phosphatidylserine (PS). Others showed that PM-to-ER transport of cholesterol derived from other sources requires Asters (also called GRAMD1s), a family of three ER proteins that bridge between the ER and PM by binding to PS. Here, we use a cholesterol esterification assay and other measures of ER cholesterol delivery to demonstrate that Asters participate in PM-to-ER transport of LDL cholesterol in Chinese hamster ovary cells. Knockout of the gene encoding PTDSS1, the major PS-synthesizing enzyme, lowered LDL-stimulated cholesterol esterification by 85%, whereas knockout of all three Aster genes lowered esterification by 65%. The reduction was even greater (94%) when the genes encoding PTDSS1 and the three Asters were knocked out simultaneously. We conclude that Asters participate in LDL cholesterol delivery from PM to ER, and their action depends in large part, but not exclusively, on PS. The data also indicate that PS participates in another delivery pathway, so far undefined, that is independent of Asters.
Subject(s)
Cholesterol, LDL/metabolism , Membrane Proteins/metabolism , Phosphatidylserines/metabolism , Animals , Biological Transport , CHO Cells , Cell Membrane/metabolism , Cholesterol/metabolism , Cholesterol Esters/metabolism , Cricetinae , Cricetulus , Endocytosis , Endoplasmic Reticulum/metabolism , Lysosomes/metabolismABSTRACT
LDL delivers cholesterol to lysosomes by receptor-mediated endocytosis. Exit of cholesterol from lysosomes requires two proteins, membrane-bound Niemann-Pick C1 (NPC1) and soluble NPC2. NPC2 binds cholesterol with its isooctyl side chain buried and its 3beta-hydroxyl exposed. Here, we describe high-resolution structures of the N-terminal domain (NTD) of NPC1 and complexes with cholesterol and 25-hydroxycholesterol. NPC1(NTD) binds cholesterol in an orientation opposite to NPC2: 3beta-hydroxyl buried and isooctyl side chain exposed. Cholesterol transfer from NPC2 to NPC1(NTD) requires reorientation of a helical subdomain in NPC1(NTD), enlarging the opening for cholesterol entry. NPC1 with point mutations in this subdomain (distinct from the binding subdomain) cannot accept cholesterol from NPC2 and cannot restore cholesterol exit from lysosomes in NPC1-deficient cells. We propose a working model wherein after lysosomal hydrolysis of LDL-cholesteryl esters, cholesterol binds NPC2, which transfers it to NPC1(NTD), reversing its orientation and allowing insertion of its isooctyl side chain into the outer lysosomal membranes.
Subject(s)
Carrier Proteins/chemistry , Carrier Proteins/metabolism , Cholesterol/metabolism , Membrane Glycoproteins/chemistry , Membrane Glycoproteins/metabolism , Binding Sites , Crystallography, X-Ray , Humans , Intracellular Signaling Peptides and Proteins , Lysosomes/metabolism , Models, Molecular , Mutagenesis , Niemann-Pick C1 Protein , Protein Structure, TertiaryABSTRACT
Ghrelin is a 28 amino acid, appetite-stimulating peptide hormone secreted by the food-deprived stomach. Serine-3 of ghrelin is acylated with an eight-carbon fatty acid, octanoate, which is required for its endocrine actions. Here, we identify GOAT (Ghrelin O-Acyltransferase), a polytopic membrane-bound enzyme that attaches octanoate to serine-3 of ghrelin. Analysis of the mouse genome revealed that GOAT belongs to a family of 16 hydrophobic membrane-bound acyltransferases that includes Porcupine, which attaches long-chain fatty acids to Wnt proteins. GOAT is the only member of this family that octanoylates ghrelin when coexpressed in cultured endocrine cell lines with prepro-ghrelin. GOAT activity requires catalytic asparagine and histidine residues that are conserved in this family. Consistent with its function, GOAT mRNA is largely restricted to stomach and intestine, the major ghrelin-secreting tissues. Identification of GOAT will facilitate the search for inhibitors that reduce appetite and diminish obesity in humans.
Subject(s)
Acyltransferases/genetics , Acyltransferases/metabolism , Caprylates/metabolism , Ghrelin/metabolism , Amino Acid Sequence , Animals , Cloning, Molecular , Gene Expression Profiling , Genome , Humans , Membrane Proteins , Mice , Molecular Sequence Data , Organ Specificity , Protein Precursors/genetics , Protein Precursors/metabolism , RNA, Messenger/metabolism , Rats , Sequence AlignmentABSTRACT
Animal cells acquire cholesterol from receptor-mediated uptake of low-density lipoprotein (LDL), which releases cholesterol in lysosomes. The cholesterol moves to the endoplasmic reticulum (ER), where it inhibits production of LDL receptors, completing a feedback loop. Here we performed a CRISPR-Cas9 screen in human SV589 cells for genes required for LDL-derived cholesterol to reach the ER. We identified the gene encoding PTDSS1, an enzyme that synthesizes phosphatidylserine (PS), a phospholipid constituent of the inner layer of the plasma membrane (PM). In PTDSS1-deficient cells where PS is low, LDL cholesterol leaves lysosomes but fails to reach the ER, instead accumulating in the PM. The addition of PS restores cholesterol transport to the ER. We conclude that LDL cholesterol normally moves from lysosomes to the PM. When the PM cholesterol exceeds a threshold, excess cholesterol moves to the ER in a process requiring PS. In the ER, excess cholesterol acts to reduce cholesterol uptake, preventing toxic cholesterol accumulation. These studies reveal that one lipid-PS-controls the movement of another lipid-cholesterol-between cell membranes. We relate these findings to recent evidence indicating that PM-to-ER cholesterol transport is mediated by GRAMD1/Aster proteins that bind PS and cholesterol.
Subject(s)
Cell Membrane/metabolism , Cholesterol, LDL/metabolism , Endoplasmic Reticulum/metabolism , Lysosomes/metabolism , Phosphatidylserines/metabolism , Animals , Biological Transport , Cell Line , Cholesterol/metabolism , HumansABSTRACT
When mice are subjected to 60% calorie restriction for several days, they lose nearly all of their body fat. Although the animals lack energy stores, their livers produce enough glucose to maintain blood glucose at viable levels even after a 23-hour fast. This adaptation is mediated by a marked increase in plasma growth hormone (GH), which is elicited by an increase in plasma ghrelin, a GH secretagogue. In the absence of ghrelin, calorie-restricted mice develop hypoglycemia, owing to diminished glucose production. To determine the site of GH action, in the current study we used CRISPR/Cas9 and Cre recombinase technology to produce mice that lack GH receptors selectively in liver (L-Ghr-/- mice) or in adipose tissue (Fat-Ghr-/- mice). When subjected to calorie restriction and then fasted for 23 hours, the L-Ghr-/- mice, but not the Fat-Ghr-/- mice, developed hypoglycemia. The fall in blood glucose in L-Ghr-/- mice was correlated with a profound drop in hepatic triglycerides. Hypoglycemia was prevented by injection of lactate or octanoate, two sources of energy to support gluconeogenesis. Electron microscopy revealed extensive autophagy in livers of calorie-restricted control mice but not in L-Ghr-/- mice. We conclude that GH acts through its receptor in the liver to activate autophagy, preserve triglycerides, enhance gluconeogenesis, and prevent hypoglycemia in calorie-restricted mice, a model of famine.
Subject(s)
Autophagy , Blood Glucose/metabolism , Caloric Restriction , Growth Hormone/blood , Hypoglycemia/blood , Liver/metabolism , Starvation/blood , Animals , Blood Glucose/genetics , Chronic Disease , Disease Models, Animal , Growth Hormone/genetics , Hypoglycemia/genetics , Liver/pathology , Mice , Mice, Knockout , Starvation/genetics , Starvation/pathologyABSTRACT
Niemann-Pick C1 (NPC1), a membrane protein of lysosomes, is required for the export of cholesterol derived from receptor-mediated endocytosis of LDL. Lysosomal cholesterol export is reportedly inhibited by itraconazole, a triazole that is used as an antifungal drug [Xu et al. (2010) Proc Natl Acad Sci USA 107:4764-4769]. Here we show that posaconazole, another triazole, also blocks cholesterol export from lysosomes. We prepared P-X, a photoactivatable cross-linking derivative of posaconazole. P-X cross-linked to NPC1 when added to intact cells. Cross-linking was inhibited by itraconazole but not by ketoconazole, an imidazole that does not block cholesterol export. Cross-linking of P-X was also blocked by U18666A, a compound that has been shown to bind to NPC1 and inhibit cholesterol export. P-X also cross-linked to purified NPC1 that was incorporated into lipid bilayer nanodiscs. In this in vitro system, cross-linking of P-X was inhibited by itraconazole, but not by U18666A. P-X cross-linking was not prevented by deletion of the N-terminal domain of NPC1, which contains the initial binding site for cholesterol. In contrast, P-X cross-linking was reduced when NPC1 contained a point mutation (P691S) in its putative sterol-sensing domain. We hypothesize that the sterol-sensing domain has a binding site that can accommodate structurally different ligands.
Subject(s)
Biological Transport/genetics , Carrier Proteins/metabolism , Cholesterol/metabolism , Lysosomes/metabolism , Membrane Glycoproteins/metabolism , Triazoles/pharmacology , Androstenes/pharmacology , Animals , Antifungal Agents/pharmacology , Binding Sites/genetics , CHO Cells , Cell Line , Cricetulus , Endocytosis/physiology , Itraconazole/pharmacology , Ketoconazole/pharmacology , Protein Binding/physiology , Protein Domains/geneticsABSTRACT
Insulin increases lipid synthesis in liver by activating transcription of the gene encoding sterol regulatory element-binding protein-1c (SREBP-1c). SREBP-1c activates the transcription of all genes necessary for fatty acid synthesis. Insulin induction of SREBP-1c requires LXRα, a nuclear receptor. Transcription of SREBP-1c also requires transcription factor C/EBPß, but a connection between LXRα and C/EBPß has not been made. Here we show that LXRα and C/EBPß form a complex that can be immunoprecipitated from rat liver nuclei. Chromatin immunoprecipitation assays showed that the LXRα-C/EBPß complex binds to the SREBP-1c promoter in a region that contains two binding sites for LXRα and is known to be required for insulin induction. Knockdown of C/EBPß in fresh rat hepatocytes or mouse livers in vivo reduces the ability of insulin to increase SREBP-1c mRNA. The LXRα-C/EBPß complex is bound to the SREBP-1c promoter in the absence or presence of insulin, indicating that insulin acts not by increasing the formation of this complex, but rather by activating it.