BPI fold containing family A, member 4 (BPIFA4) is a non-human protein encoded by the ''Bpifa4'' gene in monkey and cow. It is also known as Latherin in horse, encoded by the ''Lath/Bpifa4'' gene but somewhat divergent from the other species. Latherin/BPIFA4 is a secreted protein found in saliva and sweat. In humans, no protein is normally expressed and BPIFB5P is present only as a

pseudogene Pseudogenes are nonfunctional segments of DNA that resemble functional genes. Most arise as superfluous copies of functional genes, either directly by DNA duplication or indirectly by Reverse transcriptase, reverse transcription of an mRNA trans ...

''BPIFB5P''. However, it has appeared as a secreted product in breast cancer cell lines, previously named BASE (''b''reast cancer ''a''nd ''s''alivary gland ''e''xpression) protein.

Superfamily

BPIFA3 is a member of a BPI fold

protein superfamily A protein superfamily is the largest grouping (clade) of proteins for which common ancestry can be inferred (see homology (biology), homology). Usually this common ancestry is inferred from structural alignment and mechanistic similarity, even if n ...

defined by the presence of the bactericidal/permeability-increasing protein fold (BPI fold) which is formed by two similar domains in a "boomerang" shape. This superfamily is also known as the BPI/LBP/PLUNC family or the BPI/ LPB/ CETP family. The BPI fold creates apolar binding pockets that can interact with hydrophobic and amphipathic molecules, such as the acyl carbon chains of lipopolysaccharide found on Gram-negative bacteria, but members of this family may have many other functions. BPIFfamily-BPIF-A4P

Genes for the BPI/LBP/PLUNC superfamily are found in all vertebrate species, including distant homologs in non-vertebrate species such as insects, mollusks, and roundworms. Within that broad grouping is the BPIF gene family whose members encode the BPI fold

structural motif In a polymer, chain-like biological molecule, such as a protein or nucleic acid, a structural motif is a common Biomolecular structure#Tertiary structure, three-dimensional structure that appears in a variety of different, evolutionarily unrel ...

and are found clustered on a single chromosome, e.g., Chromosome 20 in humans, Chromosome 2 in mouse, Chromosome 3 in rat, Chromosome 17 in pig, Chromosome 13 in cow. The BPIF gene family is split into two groupings, BPIFA and BPIFB. In humans, BIPFA consists of 3 protein encoding genes ''

BPIFA1 BPI fold containing family A, member 1 (BPIFA1), also known as Palate, lung, and nasal epithelium clone (PLUNC), is a protein that in humans is encoded by the ''BPIFA1'' gene. It was also formerly known as "Secretory protein in upper respiratory ...

'', ''

BPIFA2 BPI fold containing family A, member 2 (BPIFA2), also known as Parotid Secretory Protein (PSP), is a protein that in humans is encoded by the ''BPIFA2'' gene. The ''BPIFA2'' gene sequence predicts multiple transcripts ( splice variants); 2 mRNA ...

'', '' BPIFA3'', and 1 pseudogene ''BPIFA4P''; while BPIFB consists of 5 protein encoding genes '' BPIFB1'', ''

BPIFB2 BPI fold-containing family B, member 2, (BPIFB2) also known as bactericidal/permeability-increasing protein-like 1, (BPI-like 1) is a protein that in humans is encoded by the ''BPIFB2'' gene. Superfamily BPIFB2 is a member of a BPI fold prote ...

'', ''

BPIFB3 BPI fold containing family B, member 3 (BPIFB3) is a protein that in humans is encoded by the ''BPIFB3'' gene. Two variants have been detected in humans. Superfamily BPIFB3 is a member of a BPI fold protein superfamily defined by the prese ...

'', '' BPIFB4'', ''

BPIFB6 BPI fold containing family B, member 6 (BPIFB6), also known as bactericidal/permeability-increasing protein-like 3 (BPIL3), is a protein that in humans is encoded by the ''BPIFB6'' gene, also known as ''BPIL3'' and ''LPLUNC6''. It is expressed ...

'' and 2 pseudogenes '' BPIFB5P'', ''

BPIFB9P Vomeromodulin is a non-human protein also known as BPI fold containing family B, member 9 (BPIFB9) in the rat encoded by the ''Bpifb9/RYF3'' gene, and as BPI fold containing family B, member 9A (BPIFB9A) encoded by the ''Bpifb9a'' gene in the m ...

''. What appears as pseudogenes in humans may appear as fully functional genes in other species.

Function

In humans, the expression of the ''BPIFA4P'' pseudogene into functional BPIFA4 protein is unclear. Although identified as a pseudogene not capable of coding for a protein, the RNA sequence for a putative protein has been detected at moderate levels in several glands (including salivary and mammillary), skin, and breast cancer. This is consistent with the expression of normal BPIFA4/Latherin found in saliva and sweat of other species such as cow, horse, and sheep. The function of BPIFA4 in those species is associated with BPIFA gene family members' properties of being a

surfactant Surfactants are chemical compounds that decrease the surface tension between two liquids, between a gas and a liquid, or interfacial tension between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming ...

and binding to bacterial lipopolysaccharides. Sweat helps animals cool down, and in animals with pelts (fur) BPIFA4/Latherin significantly reduces surface tension of sweat, acting as a wetting agent to facilitate evaporative cooling. Further, it is speculated that the presence of a surfactant protein in the saliva of ruminant animals (e.g., cow, horse, sheep) may assist in

mastication Chewing or mastication is the process by which food is crushed and ground by teeth. It is the first step of digestion, and it increases the surface area of foods to allow a more efficient break down by enzymes. During the mastication process, th ...

of large quantities of vegetable matter in their diet. BPIFA4 in saliva also may function as a first line of defense against bacteria, via bactericidal functions similar to other BIPFA and BIPFB family members.

References

External links

* {{UCSC gene info, BPIFA4P Pseudogenes Genes on human chromosome 20