Retinol binding protein 4

Retinol binding protein 4, plasma
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Available structures PDB Ortholog search: PDBe, RCSB List of PDB id codes 1BRP, 1BRQ, 1JYD, 1JYJ, 1QAB, 1RBP, 1RLB, 2WQ9, 2WQA, 2WR6, 3BSZ, 3FMZ, 4O9S, 4PSQ
Identifiers
Symbols	RBP4 ; MCOPCB10; RDCCAS
External IDs	OMIM: 180250 MGI: 97879 HomoloGene: 4908 ChEMBL: 3100 GeneCards: RBP4 Gene
Gene ontology Molecular function • protein binding • retinal binding • retinol binding • retinol transporter activity • protein heterodimerization activity Cellular component • extracellular region • extracellular space • cytosol • protein complex • extracellular exosome Biological process • retinoid metabolic process • eye development • gluconeogenesis • heart development • visual perception • phototransduction, visible light • maintenance of gastrointestinal epithelium • lung development • positive regulation of insulin secretion • response to retinoic acid • retinol transport • retinol metabolic process • glucose homeostasis • response to ethanol • embryonic organ morphogenesis • embryonic skeletal system development • cardiac muscle tissue development • female genitalia morphogenesis • positive regulation of immunoglobulin secretion • negative regulation of cardiac muscle cell proliferation • embryonic retina morphogenesis in camera-type eye • uterus development • vagina development • urinary bladder development • heart trabecula formation Sources: Amigo / QuickGO
RNA expression pattern
More reference expression data
Orthologs
Species	Human	Mouse
Entrez	5950	19662
Ensembl	ENSG00000138207	ENSMUSG00000024990
UniProt	P02753	Q00724
RefSeq (mRNA)	NM_006744	NM_001159487
RefSeq (protein)	NP_006735	NP_001152959
Location (UCSC)	Chr 10: 93.59 – 93.6 Mb	Chr 19: 38.12 – 38.13 Mb
PubMed search	[1]	[2]

Retinol binding protein 4, plasma, also known as RBP4, is a protein that in humans is encoded by the RBP4 gene.

Function

This protein belongs to the lipocalin family and is the specific carrier for retinol (vitamin A alcohol) in the blood. It delivers retinol from the liver stores to the peripheral tissues. In plasma, the RBP-retinol complex interacts with transthyretin, which prevents its loss by filtration through the kidney glomeruli. A deficiency of vitamin A blocks secretion of the binding protein posttranslationally and results in defective delivery and supply to the epidermal cells.

Clinical significance

Retinol-binding protein 4 has recently been described as an adipokine that contributes to insulin resistance in the AG4KO mouse model. It is secreted by adipocytes, and can act as a signal to other cells, when there is a decrease in plasma glucose concentration.

Mutations in the RBP4 gene have recently been linked to a form of autosomal dominant microphthalmia, anophthalmia, and coloboma (MAC) disease. A unique feature of this disease is the maternal inheritance effect, meaning the disease occurs when a fetus inherits a mutated copy of the RBP4 gene from its mother, but not its father. The physiologic basis lies in pregnancy whereby the mutated gene product, retinol binding protein (RBP), has negative effects in transferring vitamin A from maternal liver storage sites to the placenta, and then again on the fetal circulation side when delivering vitamin A from the placenta to developing fetal tissues, most notably the developing eye. This 'double whammy' effect does not exist when the mutant RBP4 gene is inherited from the father. The above mechanism is separate from previously known types of maternal inheritance effects such as genomic imprinting, mitochondrial inheritance, or maternal oocyte mRNA transfer. The authors of the above study cite the potential of vitamin A supplementation in pregnant females who are known to carry an RBP4 mutation with retinyl ester which utilizes an RBP-independent pathway to deliver retinoids from the maternal intestines directly to the placenta and ultimately is uptaken by the fetus. The key would be to supplement during the first several months of life when the eye begins to develop, as supplementing later in pregnancy would be too late to avoid any potential MAC disease.

See also

• Retinol binding protein

External links

• RBP4 protein, human at the US National Library of Medicine Medical Subject Headings (MeSH)