Latherin - a surface active protein from horse sweat

Latherin - a surface active protein from horse sweat

Our interest in surfactant proteins now extends to latherin, which is a detergent-like protein present in horse sweat.  Horses are flight animals and have a problem in dissipating heat when exercising.  To do this they sweat heavily, which is an unusual form of thermoregulation in mammals, although humans do it.  Human sweat is high in salt and low in protein, but horse sweat is the other way around.  Latherin is one of the most abundant proteins in horse sweat, and was originally described by John Beeley and David Eckersall at this university.  Latherin is the protein that causes the foaming of a sweating horse, particularly where harness and saddle rub.  Its function is probably to wet the hair and facilitate the rapid translocation of sweat water from the skin to the surface of the pelt to allow evaporative cooling.  We have cloned cDNA encoding latherin and can now make it with the help of bacteria but without horses.  This recombinant form of the protein is highly surface active.  We have now found that it is also produced in the salivary glands of horses, and that it is also made by zebras, onagers and wild asses.  The amino acid sequence of latherin shows that it is a member of a mysterious family of proteins, the PLUNCs, that are produced in various forms in the oral and upper respiratory tracts of humans.  So, in horses, latherin may have originally been a salivary protein that has been adapted to facilitate the action of sweat, and its surfactant activity in the mouth may be useful in dealing with the dry, fibrous diet to which horses and their kind appear to be specialised.

(Photo courtesy of Reuters)