科研之友
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摘要
Milk lipid is secreted by a unique process, during which triacylglycerol droplets bud from mammary cells coated with an outer bilayer of apical membrane. In all current schemes, the integral protein butyrophilin 1A1 (B ) is postulated to serve as a transmembrane scaffold, which interacts either with itself or with the peripheral proteins, xanthine oxidoreductase (XOR) and possibly perilipin-2 (PLIN2), to form an immobile bridging complex between the droplet and apical surface. In one such scheme, B on the surface of cytoplasmic lipid droplets interacts directly with B in the apical membrane without binding to either XOR or PLIN2. We tested these models using both biochemical and morphological approaches. B was concentrated in the apical membrane in all species examined and contained mature N-linked glycans. We found no evidence for the association of unprocessed B with intracellular lipid droplets. B -enhanced green fluorescent protein was highly mobile in areas of mouse milk-lipid droplets that had not undergone post-secretion changes, and endogenous mouse B comprised only 0.5-0.7% (w/w) of the total protein, i.e. over 50-fold less than in the milk-lipid droplets of cow and other species. B is the major component of an immobile global adhesive complex and suggest that interactions between B and other proteins at the time of secretion are more transient than previously predicted. B in lipid droplets marks it as a potential mobile signaling molecule in milk.
- 出版日期2013-9
