PLATYPUS INSULIN - INDICATIONS FROM THE AMINO-ACID-SEQUENCE OF SIGNIFICANT DIFFERENCES IN STRUCTURE FROM PORCINE INSULIN

Insulin from a monotreme, the platypus (Ornithorhynchus anatinus), was isolated and the amino acid sequence determined, It differs from pig insulin at eleven amino acid sites, mainly on the surface of the monom er. Substitutions relative to pig insulin occur in the monomer-monomer interface, the dimer-dimer interface and the receptor binding region, The residues A5 Glu, A8 Lys and A13 Met have not been reported before in any insulin, Multiple sequence comparison studies reveal a relativ ely close relationship with the nearest group of relatives to the plat ypus, the mammals. The relationship of the platypus sequence to reptil ian insulin sequences (and amphibian and avian insulin sequences in th is case) is sufficiently close to support the observation that platypu s has retained some ancient reptilian characteristics over the course of evolution. Model building the platypus insulin sequence on the stru cture of porcine insulin indicates that there may be some interesting differences.