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      Regulation of acyl-CoA:diacylglycerol acyltransferase-1 by protein phosphorylation

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      Jiayi_Han_Thesis.pdf (2.009Mb)
      Date
      2011-06
      Author
      Han, Jiayi
      Type
      Thesis
      Degree Level
      Masters
      Metadata
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      Abstract
      Triacylglycerols are the predominant molecules of energy storage in eukaryotes. Triacylglycerol synthesis is catalyzed by acyl-CoA:diacylglycerol acyltransferase (DGAT) enzymes, DGAT1 and DGAT2. Although the use of molecular tools, including targeted disruption of either DGAT enzyme, has shed light on their metabolic functions, little is known about the mechanisms responsible for regulating DGAT activity. Several lines of evidence from previous studies have suggested that DGAT1, but not DGAT2, is subject to regulation by phosphorylation and that protein kinase A (PKA)-dependent pathways are likely involved. In this study, the role of PKA in regulating DGAT activity and triacylglycerol synthesis during lipolysis was investigated. By using 3T3-L1 adipocytes, in vitro DGAT activity was shown to increase 2 fold during lipolysis. This data suggests that PKA might phosphorylate and activate DGAT1 during lipolysis to promote the recycling/re-esterification of excessive free fatty acids into triacylglycerols before they reach toxic levels within the cell. Additionally, high-performance liquid chromatography – electrospray ionization – mass spectrometry/mass spectrometry was exploited to identify PKA phosphorylation sites of DGAT1, and serine-17, -20 and -25 were identified as potential PKA phosphorylation sites using this methodology. The functional importance of these three potential phosphorylation sites was examined. Mutations of these sites to alanines (to prevent phosphorylation) or aspartates (to mimic phosphorylation) gave rise to enzymes functioning similarly to wild-type DGAT1. These phosphorylation sites appeared to be functionally silent as they were not involved in regulating DGAT1 activity, multimer formation, or enzyme stability. However, PKA phosphorylation at these three sites seemed to play a role in affinity of DGAT1 for its diacylglycerol substrate. These results indicate the existence of other unidentified, functionally active PKA phosphorylation sites or phosphorylation sites of other kinases, which are involved in regulating DGAT1.
      Degree
      Master of Science (M.Sc.)
      Department
      Biochemistry
      Program
      Biochemistry
      Supervisor
      Stone, Scot
      Committee
      Qiu, Xiao; Khandelwal, Ramji; Moore, Stanley; Pato, Mary
      Copyright Date
      June 2011
      URI
      http://hdl.handle.net/10388/etd-06152011-123626
      Subject
      phosphorylation
      protein kinase A
      mass spectrometry
      triacylglycerols
      acyl-CoA: diacylglycerol acyltransferase
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