Vitamin D-binding protein (IPR000213)

Short name: VitD-bd

Overlapping homologous superfamilies


Family relationships

  • ALB/AFP/VDB (IPR000264)
    • Vitamin D-binding protein (IPR000213)


A number of serum transport proteins are known to be evolutionarily related, including albumin, alpha-fetoprotein, vitamin D-binding protein and afamin [PMID: 2481749, PMID: 2423133, PMID: 7517938]. Albumin is the main protein of plasma; it binds water, cations (such as Ca2+, Na+ and K+), fatty acids, hormones, bilirubin and drugs - its main function is to regulate the colloidal osmotic pressure of blood. Alphafeto- protein (alpha-fetoglobulin) is a foetal plasma protein that binds various cations, fatty acids and bilirubin. The biological role of afamin (alpha-albumin) has not yet been characterised. Vitamin D-binding protein (DBP) is an abundant serum glycoprotein secreted by the liver; the protein transports vitamin D sterols, binds to actin, and is found on the surface of B-lymphocytes and subpopulations of T-lymphocytes [PMID: 2419332]. The full length DBP contains 476-amino acids, including a 16-amino acid signal sequence. Sequence analysis reveals 23% similarity to albumin and to alpha-fetoprotein [PMID: 2419332]. DBP contains a characteristic placement of cysteine residues, identical to that in albumin, suggesting a similar folding structure. Albumin and alpha-fetoprotein contain three internally repeated domains [PMID: 2419332]. DBP shows similarity to the first two domains and has a truncated third domain, supporting the view that DBP is a member of the albumin/alpha-fetoprotein multigene family [PMID: 2419332]. Within the sequence, regularly-spaced disulphide bridges generate a 3-domain folding structure, each domain containing ~170 amino acids, with 5 or 6 internal disulphide bonds, as shown schematically below:

                    +---+          +----+                        +-----+
                    |   |          |    |                        |     |
   |                 |       |     |              |               |
   +-----------------+       +-----+              +---------------+

GO terms

Biological Process

GO:0051180 vitamin transport

Molecular Function

GO:0005499 vitamin D binding
GO:0090482 vitamin transmembrane transporter activity

Cellular Component

GO:0005615 extracellular space

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.