Evolutionary origins of a bioactive peptide buried within Preproalbumin

Plant Cell. 2014 Mar;26(3):981-95. doi: 10.1105/tpc.114.123620. Epub 2014 Mar 28.


The de novo evolution of proteins is now considered a frequented route for biological innovation, but the genetic and biochemical processes that lead to each newly created protein are often poorly documented. The common sunflower (Helianthus annuus) contains the unusual gene PawS1 (Preproalbumin with SFTI-1) that encodes a precursor for seed storage albumin; however, in a region usually discarded during albumin maturation, its sequence is matured into SFTI-1, a protease-inhibiting cyclic peptide with a motif homologous to unrelated inhibitors from legumes, cereals, and frogs. To understand how PawS1 acquired this additional peptide with novel biochemical functionality, we cloned PawS1 genes and showed that this dual destiny is over 18 million years old. This new family of mostly backbone-cyclic peptides is structurally diverse, but the protease-inhibitory motif was restricted to peptides from sunflower and close relatives from its subtribe. We describe a widely distributed, potential evolutionary intermediate PawS-Like1 (PawL1), which is matured into storage albumin, but makes no stable peptide despite possessing residues essential for processing and cyclization from within PawS1. Using sequences we cloned, we retrodict the likely stepwise creation of PawS1's additional destiny within a simple albumin precursor. We propose that relaxed selection enabled SFTI-1 to evolve its inhibitor function by converging upon a successful sequence and structure.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amino Acid Sequence
  • Evolution, Molecular*
  • Molecular Sequence Data
  • Peptides / chemistry
  • Peptides / genetics*
  • Phylogeny
  • Prealbumin / chemistry
  • Prealbumin / genetics*
  • Protein Precursors / chemistry
  • Protein Precursors / genetics
  • Seeds / genetics
  • Sequence Homology, Amino Acid


  • Peptides
  • Prealbumin
  • Protein Precursors
  • preproalbumin