NDLI: Phosphorylation of Sar1b Protein Releases Liver Fatty Acid-binding Protein from Multiprotein Complex in Intestinal Cytosol Enabling It to Bind to Endoplasmic Reticulum (ER) and Bud the Pre-chylomicron Transport Vesicle

Content Provider	Journal of Biological Chemistry (JBC)
Author	Siddiqi, Shahzad Ii, Charles M. Mansbach Mansbach, Charles M.
Abstract	Native cytosol requires ATP to initiate the budding of the pre-chylomicron transport vesicle from intestinal endoplasmic reticulum (ER). When FABP1 alone is used, no ATP is needed. Here, we test the hypothesis that in native cytosol FABP1 is present in a multiprotein complex that prevents FABP1 binding to the ER unless the complex is phosphorylated. We found on chromatography of native intestinal cytosol over a Sephacryl S-100 HR column that FABP1 (14 kDa) eluted in a volume suggesting a 75-kDa protein complex that contained four proteins on an anti-FABP1 antibody pulldown. The FABP1-containing column fractions were chromatographed over an anti-FABP1 antibody adsorption column. Proteins co-eluted from the column were identified as FABP1, Sar1b, Sec13, and small VCP/p97-interactive protein by immunoblot, LC-MS/MS, and MALDI-TOF. The four proteins of the complex had a total mass of 77 kDa and migrated on native PAGE at 75 kDa. When the complex was incubated with intestinal ER, there was no increase in FABP1-ER binding. However, when the complex member Sar1b was phosphorylated by PKCζ and ATP, the complex completely disassembled into its component proteins that migrated at their monomer molecular weight on native PAGE. FABP1, freed from the complex, was now able to bind to intestinal ER and generate the pre-chylomicron transport vesicle (PCTV). No increase in ER binding or PCTV generation was observed in the absence of PKCζ or ATP. We conclude that phosphorylation of Sar1b disrupts the FABP1-containing four-membered 75-kDa protein complex in cytosol enabling it to bind to the ER and generate PCTV.
Related Links	http://www.jbc.org/content/287/13/10178.abstract
Ending Page	10188
Starting Page	10178
Page Count	11
File Format	HTM / HTML PDF
ISSN	00219258
Journal	Journal of Biological Chemistry (JBC)
Issue Number	13
Volume Number	287
DOI	10.1074/jbc.M111.327247
e-ISSN	1083351X
Language	English
Publisher	American Society for Biochemistry and Molecular Biology
Publisher Date	2012-03-23
Access Restriction	Open
Subject Keyword	Lipid Absorption Lipid-binding Protein Protein Kinase C (PKC) Triglyceride Vesicles Chylomicrons Liver Fatty Acid-binding Protein Protein Phosphorylation Cell Biology
Content Type	Text
Resource Type	Article
Subject	Cell Biology Biochemistry Molecular Biology

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Phosphorylation of Sar1b Protein Releases Liver Fatty Acid-binding Protein from Multiprotein Complex in Intestinal Cytosol Enabling It to Bind to Endoplasmic Reticulum (ER) and Bud the Pre-chylomicron Transport Vesicle*

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