Comparison of the Amino Acid Sequences of Hen Plasma-, Yolk-, and White-Riboflavin Binding Proteins

Abstract

The amino acid sequence of hen egg yolk-riboflavin binding protein (yolk-RBP) was determined by conventional methods. The sequence was identical with that of hen egg white-riboflavin binding protein except that their carboxyltermini were different, that of yolk-RBP lacked 11 or 13 amino acid residues, while hen plasma-RBP had the same C-terminal sequence as white-RBP. This indicated that the C-terminal 11 or 13 amino acid residues in plasma-RBP might be cleaved off during the incorporation from the blood into the oocyte or in the yolk fluid. Yolk-RBP had the same characteristics as white-RBP, such as N-terminal pyroglutamic acid, polymorphism in the amino acid sequence (Lys/Asn) at the fourteenth residue from the N-terminal end, carbohydrate chains attached to both Asn(36) and Asn(147) residues, and phosphate groups bound to some serine residues in the sequence of Ser(185) to Ser(197) as a cluster. These results led us to the conclusion that yolk- and white-RBPs are bio-synthesized from the same gene in the different organs (liver and oviduct). The carbohydrate composition of yolk-RBP was identical to that of plasma-RBP but different from that of white-RBP showing that the processing of the carbohydrate chains in the liver was different from that in the oviduct.

Specific postendocytic proteolysis of apolipoprotein B in oocytes does not abolish receptor recognition.

“…In addition to VLDL, most, if not all, yolk components are believed to be transported across the plasma membrane of the oocyte by way of specific receptors. Systems of receptor-mediated endocytosis may exist for transferrin (2,3), various vitamin-binding proteins (4)(5)(6)(7)(8)(9)(10)(11)(12), and IgG (13,14). Though direct biochemical demonstration of oocyte receptors for most of these proteins has not been reported, we have recently characterized the chicken oocyte plasma membrane proteins responsible for the transport of VLDL (1) and vitellogenin, another major yolk component (15).…”

“…This has been suggested for riboflavin-binding protein (16), which exists in three closely related but distinct forms in the laying hen that can be isolated from plasma, egg white, and yolk. The egg white form is distinguished from the other two forms by its different carbohydrate composition; the yolk protein is a truncated form of the plasma protein, lacking 11 or 13 amino acid residues at the carboxyl terminus (5,6). The carboxylterminal truncation in yolk riboflavin-binding protein has been proposed to be elicited by specific intraoocytically localized protease(s) (6,17).…”

“…The egg white form is distinguished from the other two forms by its different carbohydrate composition; the yolk protein is a truncated form of the plasma protein, lacking 11 or 13 amino acid residues at the carboxyl terminus (5,6). The carboxylterminal truncation in yolk riboflavin-binding protein has been proposed to be elicited by specific intraoocytically localized protease(s) (6,17). Another example of specific postendocytic processing is provided by the vitellogenins, a family of glycophospholipoproteins with molecular masses of -240 kDa, which are degraded inside the oocyte to lipovitellin(s) (the amino-terminal portion of vitellogenins), phosvitin(s) (the central, phosphoserine/serine-rich domain), and carboxyl-terminal polypeptides termed phosvettes or lipovitellin(s) II.…”

Complete Mapping of Divergent Amino Acids Responsible for Differential Ligand Binding of Folate Receptors α and β

“…A Structural Model of FR-FR shows considerable (ϳ30%) amino acid sequence identity with the 219-residue chicken riboflavin-binding protein (cRBP) (53). The amino acid sequence alignment of the two proteins has been reported (46).…”

Riboflavin binding protein contains a type II copper binding site

“…This protein binds riboflavin, a nutrient essential for embryonic development, in a 1:1 molar ratio, and transports the nutrient into the egg. There are several isoforms of RBP in the egg that vary slightly in size, due to loss of amino acids residues at the N-terminus, and to variations in phosphorylation and glycosylation post-translational modifications [1,2]. The egg white form (wRBP) is produced in the oviduct, and the yolk form (yRBP) is produced in the liver and transported to the developing oocyte [2][3][4][5].…”