A novel multiprotein complex is required to generate the prechylomicron transport vesicle from intestinal ER.

Dietary lipid absorption is dependent on chylo- micron production whose rate-limiting step across the intes- tinal absorptive cell is the exit of chylomicrons from the endoplasmic reticulum (ER) in its ER-to-Golgi transport vesicle, the prechylomicron transport vesicle (PCTV). This study addresses the composition of the budding complex for PCTV. Immunoprecipitation (IP) studies from rat intes- tinal ER solubilized in Triton X-100 suggested that vesicle- associated membrane protein 7 (VAMP7), apolipoprotein B48 (apoB48), liver fatty acid-binding protein (L-FABP), CD36, and the COPII proteins were associated on incuba- tion of the ER with cytosol and ATP. This association was confi rmed by chromatography of the solubilized ER over Sephacryl S400-HR in which these constituents cochromato- graphed with an apparent kDa of 630. No multiprotein com- plex was detected when the ER was chromatographed in the absence of PCTV budding activity (resting ER or PKC de- pletion of ER and cytosol). Treatment of the ER with anti- apoB48 or anti-VAMP7 antibodies or using gene disrupted L-FABP or CD36 mice all signifi cantly inhibited PCTV gen- eration. A smaller complex (no COPII proteins) was formed when only rL-FABP was used to bud PCTV. The data sup- port the conclusion that the PCTV budding complex in in- testinal ER is composed of VAMP7, apoB48, CD36, and L-FABP, plus the COPII proteins. —Siddiqi, S., U. Saleem, N. Abumrad, N. Davidson, J. Storch, S. A. Siddiqi, and C. M. Mansbach II. A novel multiprotein complex is required to generate the prechylomicron transport vesicle from intesti- nal ER. J. Lipid Res. 2010. 51: 1918-1928.