title: Mature forms of the major seed storage albumins in sunflower: A mass spectrometric approach.
abstract: Seed storage albumins are abundant, water-soluble proteins that are degraded to provide critical nutrients for the germinating seedling. It has been established that the sunflower albumins encoded by SEED STORAGE ALBUMIN 2 (SESA2), SESA20 and SESA3 are the major components of the albumin-rich fraction of the common sunflower Helianthus annuus. To determine the structure of sunflowers most important albumins we performed a detailed chromatographic and mass spectrometric characterization to assess what post-translational processing they receive prior to deposition in the protein storage vacuole. We found that SESA2 and SESA20 each encode two albumins. The first of the two SESA2 albumins (SESA2-1) exists as a monomer of 116 or 117 residues, differing by a threonine at the C-terminus. The second of the two SESA2 albumins (SESA2-2) is a monomer of 128 residues. SESA20 encodes the albumin SESA20-2, which is a 127-residue monomer, whereas SESA20-1 was not abundant enough to be structurally described. SESA3, which has been partly characterized previously, was found in several forms with methylation of its asparagine residues. In contrast to other dicot albumins, which are generally matured into a heterodimer, all the dominant mature sunflower albumins SESA2, SESA20-2, SESA3 and its post-translationally modified analogue SESA3-a are monomeric.
  
  
  
  Sunflower plants have been bred to thrive in various climate zones making them favored crops to meet the growing worldwide demand by humans for protein. The abundance of seed storage proteins makes them an important source of protein for animal and human nutrition. This study explores the structures of the dominant sunflower napin-type seed storage albumins to understand what structures evolution has favored in the most abundant proteins in sunflower seed.
authors.affiliation: The University of Queensland, School of Biomedical Sciences, Brisbane, QLD 4072, Australia.
authors.forename: Bastian
authors.initials: B
authors.lastname: Franke
authors.affiliation: CSIRO Agriculture, 306 Carmody Road, St Lucia, QLD 4067, Australia.
authors.forename: Michelle L
authors.initials: ML
authors.lastname: Colgrave
authors.affiliation: The University of Western Australia, School of Chemistry and Biochemistry & ARC Centre of Excellence in Plant Energy Biology, 35 Stirling Highway, Crawley, Perth 6009, Australia.
authors.forename: Joshua S
authors.initials: JS
authors.lastname: Mylne
authors.affiliation: The University of Queensland, School of Biomedical Sciences, Brisbane, QLD 4072, Australia. Electronic address: j.rosengren@uq.edu.au.
authors.forename: K Johan
authors.initials: KJ
authors.lastname: Rosengren
mesh_terms: D000418:Albumins / Q000032:analysis*; D002845:Chromatography; D006368:Helianthus / Q000737:chemistry*; D013058:Mass Spectrometry; D010940:Plant Proteins / Q000032:analysis; D011499:Protein Processing, Post-Translational; D040901:Proteomics / Q000379:methods*; D055314:Seed Storage Proteins / Q000032:analysis* / Q000378:metabolism
chemical_list: D000418:Albumins; D010940:Plant Proteins; D055314:Seed Storage Proteins
keywords: Asparaginyl endopeptidase (AEP); Helianthus annuus; Napin; Post-translational processing; Seed storage albumin