Antigen: human sRBP4 amino acids 28-37 (RVKENFDKAR) · Host: rabbit · Application(s): WB · Serum retinol binding protein 4 (sRBP4) binds one equivalent of vitamin A and is one of the major retinol carriers found in the blood of mammals.^1,2 Human RBP4 is a monomeric 21 kDa β-sheet-rich protein that contains three disulfide bonds and belongs to the lipocalin protein family.³ sRBP4 is synthesized and sequestered in hepatocytes until retinol binding triggers its secretion.³ In plasma, sRBP4 typically forms a 1:1 complex with the 55 kDa tetrameric protein transthyretin (TTR) which prevents RBP from being removed from the plasma by glomerular filtration.⁴ Recent studies have shown that sRBP4 is an adipocyte-derived “signal” that may contribute to the pathogenesis of type 2 diabetes.^5,6 Elevation of sRBP4 causes systemic insulin resistance whereas reduction of serum concentrations improves insulin action.^5,7,8 The highest known concentrations of this protein exist in serum, liver, and skeletal muscle.^9,10,11

1 Noy, N. Retinoid-binding proteins: Mediators of retinoid action. Biochem J 348 481-495 (2000).

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3 Cowan, S.W., Newcomer, M.E., and Jones, T.A. Crystallographic refinement of human serum retinol binding protein at 2Å resolution. Proteins 8 44-61 (1990).

4 Sivaprasadarao, A., and Findlay, J.B.C. Expression of functional human retinol-binding protein in Escherichia coli using a secretion vector. Biochem J 296 209-215 (1993).

5 Yang, Q., Graham, T.E., Mody, N., et al. Serum retinol binding protein 4 contributes to insulin resistance in obesity and type 2 diabetes. Nature 436 356-362 (2005).

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9 Polonsky, K.S. Retinol-binding protein 4, insulin resistance, and type 2 diabetes. N Engl J Med 354(24) 2596-2598 (2006).

10 Tamori, Y., Sakaue, H., and Kasuga, M. RBP4, an unexpected adipokine. Nat Med 12(1) 30-31 (2006).

11 missing reference text

Noy, N. Retinoid-binding proteins: Mediators of retinoid action. Biochem J 348 481-495 (2000).

Cowan, S.W., Newcomer, M.E., and Jones, T.A. Crystallographic refinement of human serum retinol binding protein at 2Å resolution. Proteins 8 44-61 (1990).

Yang, Q., Graham, T.E., Mody, N., et al. Serum retinol binding protein 4 contributes to insulin resistance in obesity and type 2 diabetes. Nature 436 356-362 (2005).

Graham, T.E., Yang, Q., Blüher, M., et al. Retinol-binding protein 4 and insulin resistance in lean, obese, and diabetic subjects. N Engl J Med 354(24) 2552-2563 (2006).

Tamori, Y., Sakaue, H., and Kasuga, M. RBP4, an unexpected adipokine. Nat Med 12(1) 30-31 (2006).

Polonsky, K.S. Retinol-binding protein 4, insulin resistance, and type 2 diabetes. N Engl J Med 354(24) 2596-2598 (2006).

Muoio, D.M., and Newgard, C.B. A is for adipokine. Nature 436 337-338 (2005).

Sivaprasadarao, A., and Findlay, J.B.C. Expression of functional human retinol-binding protein in Escherichia coli using a secretion vector. Biochem J 296 209-215 (1993).

Xie, Y., Lashuel, H.A., Miroy, G.J., et al. Recombinant human retinol-binding protein refolding, native disulfide formation, and characterization. Protein Expr Purif 14 31-37 (1998).

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