title: Evolutionary origins of a bioactive peptide buried within Preproalbumin.
abstract: 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.
authors.affiliation: The University of Queensland, Institute for Molecular Bioscience, Brisbane 4072, Australia.
authors.forename: Alysha G
authors.initials: AG
authors.lastname: Elliott
authors.forename: Christina
authors.initials: C
authors.lastname: Delay
authors.forename: Huanle
authors.initials: H
authors.lastname: Liu
authors.forename: Zaiyang
authors.initials: Z
authors.lastname: Phua
authors.forename: K Johan
authors.initials: KJ
authors.lastname: Rosengren
authors.forename: Aurélie H
authors.initials: AH
authors.lastname: Benfield
authors.forename: Jose L
authors.initials: JL
authors.lastname: Panero
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Colgrave
authors.forename: Achala S
authors.initials: AS
authors.lastname: Jayasena
authors.forename: Kerry M
authors.initials: KM
authors.lastname: Dunse
authors.forename: Marilyn A
authors.initials: MA
authors.lastname: Anderson
authors.forename: Edward E
authors.initials: EE
authors.lastname: Schilling
authors.forename: Daniel
authors.initials: D
authors.lastname: Ortiz-Barrientos
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Mylne
mesh_terms: D000595:Amino Acid Sequence; D019143:Evolution, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry / Q000235:genetics*; D010802:Phylogeny; D011228:Prealbumin / Q000737:chemistry / Q000235:genetics*; D011498:Protein Precursors / Q000737:chemistry / Q000235:genetics; D012639:Seeds / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D010455:Peptides; D011228:Prealbumin; D011498:Protein Precursors; C014771:preproalbumin