Primary Structure of Porcine Tropoelastin

Abstract

Structural studies on porcine aortic tropoelastin as obtained from copper-deficient swine have been performed on the whole protein as well as fragments produced by trypsin, subtilisin and thrombin digestion. Tryptic fragments fall into two catagories, those large, over 20 residues, and those small, 4 residues and less. Analyses of the small peptides has been accomplished by hand sequencing methods and by mass spectrometry. Analyses of the large fragments has been accomplished on the automated spinning cup amino acid sequencer. There is a striking difference in the composition of the two groups of peptides. The small ones contain a large amount of alanine, and appear to be present in sufficient amounts to indicate repeating sequences of these within the protein. The large tryptic fragments can be grouped together as those beginning with tyrosine, those beginning with alanine, and those beginning with other residues such as glycine, valine, phenylalanine and possibly leucine. The most striking feature of the large tryptic fragments is that they contain repeating structures of a tetrapeptlde, Pro-Gly-Gly-Val, of a pentapeptlde, Pro-Gly-Val-Gly-Val and of a hexapeptide, ProGly-Val-Gly-Val-Ala. They also appear to be deficient in alanine at their NH₂-termini, but enriched in this amino acid at their C-terminals. Subtilisin digestion of these large peptides gives arginine and lysine-containing fragments similar in composition to the small tryptic peptides. Only a few of the large tryptic peptides have been completely sequenced, but we do have sufficient information to indicate that at least 70% of these large fragments are over 50 residues in size. Some are over 100 residues long.