RBP4 is a single polypeptide chain with a hydrophobic pocket where retinol binds.
The RBP4-retinol complex then binds transthyretin in circulation to prevent renal filtration of RBP4.
 
In serum, TTR and RBP4 bind in a 1 to 1 stoichiometry (two molecules of TTR combine with two molecules of RBP4 to form a complex with a total molecular weight of approximately 80,000 Daltons).
RBP4 is a single polypeptide chain with a hydrophobic pocket where retinol binds. The RBP4-retinol complex then binds transthyretin in circulation to prevent renal filtration of RBP4.  
In serum, TTR and RBP4 bind in a 1 to 1 stoichiometry (two molecules of TTR combine with two molecules of RBP4 to form a complex with a total molecular weight of approximately 80,000 Daltons).
Retinol binding protein 4