Homology between the primary structures of beta-lactoglobulins and human retinol-binding protein: evidence for a similar biological function?
Two types of beta-lactoglobulins were identified and isolated from horse colostrum: beta-1g I and beta-1g II. The amino-acid sequence of some tryptic peptides from the new monomeric beta-lactoglobulin II was determined and aligned to the other beta-lactoglobulins of known sequence and to the human plasma retinol-binding protein. The comparison of the primary structures of beta-lactoglobulins and human retinol-binding protein shows an unexpectedly high homology of 25%. We found 37 identities among 149 possible homologous residues. Among them is a tryptophan residue at position 19 of beta-lg which might represent the binding site of beta-ionone. These data suggest a common origin of beta-lactoglobulin and human retinol-binding protein and imply that beta-lactoglobulins may be involved in the metabolism of retinol.
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D006736:Horses; D006801:Humans; D007782:Lactoglobulins / Q000378:metabolism; D012177:Retinol-Binding Proteins / Q000378:metabolism; D054839:Retinol-Binding Proteins, Plasma
D007782:Lactoglobulins; D012177:Retinol-Binding Proteins; D054839:Retinol-Binding Proteins, Plasma