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Recent data concerning the effect of soybean 7S globulin subunits on the upregulation of LDL receptors in Hep G2 cells identified the alpha' subunit as the candidate responsible for this biological effect. In vivo evaluation of this subunit on cholesterol homeostasis was hampered by the lack of suitable amounts of alpha' chain. A novel separation procedure allowed us to investigate the effects of alpha' subunit administration on plasma cholesterol and triglyceride levels, as well as on the activity of liver beta-VLDL receptors of rats fed a hypercholesterolemic (HC) diet. Rats were divided into 9 groups fed the following diets for 28 d: standard diet; HC diet; HC diets + 5, 10, and 20 mg/(kg body weight. d) of alpha' subunit; HC diets + 50, 100, and 200 mg/(kg body weight. d) of soybean 7S globulin; HC diet + 200 mg/(kg body weight. d) clofibrate. The highest dose of the alpha' subunit decreased plasma cholesterol and triglycerides 36 and 34%, respectively, in rats fed the HC diet; 10-fold amounts clofibrate reduced plasma cholesterol and triglycerides 38 and 41%. The activity of liver beta-VLDL receptors of rats fed the HC diet with the highest dose of the alpha' subunit had a 96% increase in binding compared with the HC diet group, thus restoring the receptor activity to that of rats fed the standard diet. These results represent the first in vivo evidence of both the plasma lipid-lowering properties and the upregulation of liver beta-VLDL receptors induced by the soybean alpha' subunit.

We found that the human intestinal isolate Bifidobacterium bifidum MIMBb75 strongly adhered to Caco-2 cells. Proteinase K and lithium chloride treatments showed that proteins play a key role in MIMBb75 adhesion to Caco-2 cells. By studying the cell wall-associated proteins, we identified a surface protein, which we labeled BopA. We purified the protein chromatographically and found that it functioned as an adhesion promoter on Caco-2 cells. In silico analysis of the gene coding for this protein and globomycin experiments showed that BopA is a cysteine-anchored lipoprotein expressed as a precursor polypeptide. A database search indicated that BopA appears to function biologically as an oligopeptide/tripeptide-solute-binding protein in the ABC transport system. We discovered a protein corresponding to BopA and its gene in eight other highly adherent B. bifidum strains. Finally, we found that B. bifidum MIMBb75 and BopA affected the production of interleukin-8 in Caco-2 epithelial cells. BopA is the first protein described to date to be directly involved in the adhesion of bifidobacteria to Caco-2 cells and to show immunomodulatory activity.

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