User:Jgedwards/Thymosins

New article name is Thymosins

Thymosins are small peptides present in animal tissues, and so-named from their original isolation from thymus. They have diverse biological functions and two in particular, thymosins α1 and β4, have potentially important uses in medicine.

Discovery
The discovery of thymosins in the mid 1970s emerged from investigations of the role of  the thymus in development of the vertebrate immune system. Begun by Allan Goldstein in the Laboratory of Abraham White at the Albert Einstein College of Medicine in New York, the work continued  at University of Texas Medical Branch in Galveston. The supposition that the role of the thymus might  involve a hormone-like mechanism led to the isolation from thymus tissue of  a biologically active preparation. Known as "Thymosin Fraction 5", this was able to restore  some aspects of immune function in animals lacking thymus gland. Fraction 5 was found to contain a number of small peptides, which were named "thymosins" and classified as α, β and γ thymosins on the basis of their behaviour in an electric field.

When individual thymosins were isolated from Fraction 5  and characterized, they were found  to have extremely varied and important biological properties. However they are not truly thymic hormones,   several are widely distributed throughout many different tissues and apart from thymosin α1 are not restricted in occurrence to thymus tissue.

Distribution
Monomeric β-thymosins, i.e. those of molecular weight similar to those originally isolated by Goldstein, are found only in cells of multicellular animals *. They are absent from some invertebrates, which do nevertheless possess proteins constructed from several end-to-end repeats of  β-thymosin sequences. Genomics has shown that tetrapods (land vertebrates) each express three β-thymosins, which are the species equivalents (orthologues) of human β4, β10 and β15 thymosins respectively. Bony fish in general express orthologues of thsee same three, plus an additional copy of the β4 orthologue.

Relation to the WH2 sequence module
The N-terminal half of β-thymosins bears a strong similarity in amino acid sequence to a very widely distributed sequence module, the WH2 (Wasp Homology 2) domain. *. Evidence from X-ray crystallography shows that this part of β-thymosins and WH2 modules  bind to actin in a near-identical manner, adopting as they bind, a  conformation which has been referred to as the  β-thymosin/WH2 fold. β-thymosins may therefore have evolved by addition of novel C-terminal sequence to an ancestral WH2 module. However, sequence similarity searches designed to identify  present-day WH2 domains * fail to recognise β-thymosins, and so the sequence and functional similarities may result  result from  convergent evolution.