In molecular biology, ephrins are a family of proteins

Protein family

A protein family is a group of evolutionarily-related proteins, and is often nearly synonymous with gene family. The term protein family should not be confused with family as it is used in taxonomy....

 that are ligands of class V (EPH-related) receptor protein-tyrosine kinases. These receptors

Receptor (biochemistry)

In biochemistry, a receptor is a molecule found on the surface of a cell, which receives specific chemical signals from neighbouring cells or the wider environment within an organism...

 and their ligands

Ligand (biochemistry)

In biochemistry and pharmacology, a ligand is a substance that forms a complex with a biomolecule to serve a biological purpose. In a narrower sense, it is a signal triggering molecule, binding to a site on a target protein.The binding occurs by intermolecular forces, such as ionic bonds, hydrogen...

 have been implicated in regulating neuronal axon guidance

Axon guidance

Axon guidance is a subfield of neural development concerning the process by which neurons send out axons to reach the correct targets...

 and in patterning of the developing nervous system

Nervous system

The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

 and may also serve a patterning and compartmentalisation role outside of the nervous system

Nervous system

The nervous system is an organ system containing a network of specialized cells called neurons that coordinate the actions of an animal and transmit signals between different parts of its body. In most animals the nervous system consists of two parts, central and peripheral. The central nervous...

.

Ephrins are membrane-attached protein

Protein

Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...

s of 205 to 340 residues

Residue (chemistry)

In chemistry, residue is the material remaining after a distillation or an evaporation, or to a portion of a larger molecule, such as a methyl group. It may also refer to the undesired byproducts of a reaction....

. Attachment appears to be crucial for their normal function. Type-A ephrins are linked to the membrane

Cell membrane

The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...

 via a glycosylphosphatidylinositol (GPI)-linkage, while type-B ephrins are type-I membrane proteins.

Types include:

• EFNA1
• EFNA2
  EFNA2
  Ephrin-A2 is a protein that in humans is encoded by the EFNA2 gene.-Further reading:...
  
  
• EFNA3
  EFNA3
  Ephrin-A3 is a protein that in humans is encoded by the EFNA3 gene.-Further reading:...
  
  
• EFNA4
  EFNA4
  Ephrin-A4 is a protein that in humans is encoded by the EFNA4 gene.-Further reading:...
  
  
• EFNA5
  EFNA5
  Ephrin-A5 is a protein that in humans is encoded by the EFNA5 gene.-Further reading:...
  
  
• EFNB1
  EFNB1
  Ephrin-B1 is a protein that in humans is encoded by the EFNB1 gene.Mutations in this protein are responsible for most cases of craniofrontonasal syndrome.-Further reading:...
  
  
• EFNB2
  EFNB2
  Ephrin-B2 is a protein that in humans is encoded by the EFNB2 gene.-Further reading:...
  
  
• EFNB3
  EFNB3
  Ephrin-B3 is a protein that in humans is encoded by the EFNB3 gene.-Further reading:...