Activities of overt and latent diacylglycerol acyltransferases (DGATs I and II) in liver microsomes of ob/ob mice

Waterman, IJ; Zammit, V A

doi:10.1038/sj.ijo.0801981

Cited by 18 publications

(8 citation statements)

References 11 publications

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“…This model agrees with previous biochemical studies in which the active site of DGAT (and that of the family member acyl-CoA:monoacylglycerol acyltransferase) was oriented toward the cytosol (24). A latent DGAT activity (present only after treating membranes with disrupting agents) has been detected in rat liver microsomes (25)(26)(27)(28), suggesting that there are active sites on both sides of the ER membrane. Our topology data suggest that DGAT2 is not responsible for this latent activity.…”

Section: Discussionsupporting

confidence: 81%

Membrane Topology and Identification of Key Functional Amino Acid Residues of Murine Acyl-CoA:Diacylglycerol Acyltransferase-2

Stone

Levin

Farese

2006

Journal of Biological Chemistry

197

211

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Triacylglycerols are the predominant molecules of energy storage in eukaryotes. However, excessive accumulation of triacylglycerols in adipose tissue leads to obesity and, in nonadipose tissues, is associated with tissue dysfunction. Hence, it is of great importance to have a better understanding of the molecular mechanisms of triacylglycerol synthesis. The final step in triacylglycerol synthesis is catalyzed by the acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes, DGAT1 and DGAT2. Although recent studies have shed light on metabolic functions of these enzymes, little is known about the molecular aspects of their structures or functions. Here we report the topology for murine DGAT2 and the identification of key amino acids that likely contribute to enzymatic function. Our data indicate that DGAT2 is an integral membrane protein with both the N and C termini oriented toward the cytosol. A long hydrophobic region spanning amino acids 66 -115 likely comprises two transmembrane domains or, alternatively, a single domain that is embedded in the membrane bilayer. The bulk of the protein lies distal to the transmembrane domains. This region shares the highest degree of homology with other enzymes of the DGAT2 family and contains a sequence HPHG that is conserved in all family members. Mutagenesis of this sequence in DGAT2 demonstrated that it is required for full enzymatic function. Additionally, a neutral lipid-binding domain that is located in the putative first transmembrane domain was also required for full enzymatic function. Our findings provide the first insights into the topography and molecular aspects of DGAT2 and related enzymes.

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Section: Discussionsupporting

confidence: 81%

Membrane Topology and Identification of Key Functional Amino Acid Residues of Murine Acyl-CoA:Diacylglycerol Acyltransferase-2

Stone

Levin

Farese

2006

Journal of Biological Chemistry

197

211

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“…Increased expression of the gene for DGAT has been shown to promote VLDL secretion in the McA RH7777 cell line, but it also results in cellular accumulation of TG (20). In leptin-deficient (ob/ob) mice, a mouse model of diet-induced obesity and insulin resistance, both hepatic dgat1 and dgat2 activities are increased more than twofold compared with wild-type controls in conjunction with an upregulation of hepatic srebp1 gene (35) despite an absence of the sterol response element in their promoters. These mice also develop increased hepatic lipogenesis, accumulation of hepatic TG, and hepatic VLDL overproduction.…”

Section: Discussionmentioning

confidence: 99%

“…Likewise, the reduction in hepatic TG content in the face of increased lipogenesis and TG production suggests a role for additional regulatory factors. PUFA circulate mainly in the form of PL and CE, with those in TG and nonesterified fatty acid (NEFA) forming a minor component (35). The nearly complete absence of PUFA-CE in the apoB-containing lipoproteins in both ldlr Ϫ/Ϫ ϫlcat Ϫ/Ϫ and lcat Ϫ/Ϫ mice would likely impact on the hepatic abundance of PUFA as exogenous source.…”

Section: Discussionmentioning

confidence: 99%

Coordinated alteration of hepatic gene expression in fatty acid and triglyceride synthesis in LCAT-null mice is associated with altered PUFA metabolism

Song¹,

Zhu²,

Picardo³

et al. 2006

American Journal of Physiology-Endocrinology and Metabolism

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“…This difference is also supported by previous reports on rat liver and yeast DGAT enzymes. Two types of DGAT activities were detected from liver microsomes: one is overt and regulates the cytosolic TAG pools, and the other is latent and plays a role in TAG secretion (22,23). In yeast cells, inactivation of the yeast DGAT1 gene resulted in the reduction of DGAT activity on lipid particles, but without significant effect on DGAT activity in the ER (24).…”

Section: Discussionmentioning

confidence: 99%

Catalytic properties of MGAT3, a putative triacylgycerol synthase

Cao

Cheng

Shi

2007

Journal of Lipid Research

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Acyl-coenzyme A:monoacylglycerol acyltransferase 3 (MGAT3) is a member of the MGAT family of enzymes that catalyze the synthesis of diacylglycerol (DAG) from monoacylglycerol (MAG), a committed step in dietary fat absorption. Although named after the initial identification of its MGAT activity, MGAT3 shares higher sequence homology with acyl-coenzyme A:diacylglycerol acyltransferase 2 (DGAT2) than with other MGAT enzymes, suggesting that MGAT3 may also possess significant DGAT activity. This study compared the catalytic properties of MGAT3 with those of MGAT1 and MGAT2 enzymes using both MAG and DAG as substrates. Our results showed that in addition to the expected MGAT activity, the recombinant MGAT3 enzyme expressed in Sf-9 insect cells displayed a strong DGAT activity relative to that of MGAT1 and MGAT2 enzymes in the order MGAT3 . MGAT1 . MGAT2. In contrast, none of the three MGAT enzymes recognized biotinylated acyl-CoA or MAG as a substrate. Although MGAT3 possesses full DGAT activity, it differs from DGAT1 in catalytic properties and subcellular localization. The MGAT3 activity was sensitive to inhibition by the presence of 1% CHAPS, whereas DGAT1 activity was stimulated by the detergent. Consistent with high sequence homology with DGAT2, the MGAT3 enzyme demonstrated a similar subcellular distribution pattern to that of DGAT2, but not DGAT1, when expressed in COS-7 cells. Our data suggest that MGAT3 functions as a novel triacylglycerol (TAG) synthase that catalyzes efficiently the two consecutive acylation steps in TAG synthesis.-Cao, J., L. Cheng, and Y. Shi. Catalytic properties of MGAT3, a putative triacylgycerol synthase. J. Lipid Res. 2007. 48: 583-591.

show abstract

Activities of overt and latent diacylglycerol acyltransferases (DGATs I and II) in liver microsomes of ob/ob mice

Cited by 18 publications

References 11 publications

Membrane Topology and Identification of Key Functional Amino Acid Residues of Murine Acyl-CoA:Diacylglycerol Acyltransferase-2

Membrane Topology and Identification of Key Functional Amino Acid Residues of Murine Acyl-CoA:Diacylglycerol Acyltransferase-2

Coordinated alteration of hepatic gene expression in fatty acid and triglyceride synthesis in LCAT-null mice is associated with altered PUFA metabolism

Catalytic properties of MGAT3, a putative triacylgycerol synthase

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