Amino acid and cDNA sequences of a methionine‐rich 2S protein from sunflower seed (Helianthus annuus L.)

Abstract

The amino acid sequence of a methionine-rich 2s seed protein from sunflower (Heliunthus annuus L.) and the sequence of a cDNA clone which codes for the entire primary translation product have been determined. The mature protein consists of a single polypeptide chain of 103 amino acids (molecular mass 12133 Da) which contains 16 residues of methionine and 8 residues of cysteine. The cDNA sequence established that the protein is synthesized as a precursor of 141 residues with a typical hydrophobic signal sequence of 25 residues followed by a further 13-residue hydrophobic pro-sequence which is presumably removed by post-translational cleavage. The sequence of the mature protein and that deduced from the cDNA were identical with no evidence of processing at the C-terminus. Comparison of the sunflower methionine-rich protein sequence with sequences of other seed 2s proteins from dicotyledons and monocotyledons showed limited but distinct sequence similarities; in particular the arrangement of the cysteine residues was conserved. The sunflower protein shows 34% identity with the methionine-rich Brazil nut 2s protein and the prepro regions of the precursors of these two proteins show about 50% identity. This similarity indicates that these methionine-rich 2s proteins have diverged as a subclass of the 2s superfamily of proteins which contain only 2-3% methionine. While the related 2s proteins from other dicotyledons are processed to a small and large subunit, the sunflower protein is not cleaved in this way.The seed storage proteins of most dicotyledonous plants contain two major protein classes, globulins and albumins, which are distinguished on the basis of solubility [l]. These proteins are expressed during seed development as precursors which undergo co-and post-translational modification prior to deposition in protein bodies [2]. The globulins, which are soluble in high-salt buffers and have sedimentation coefficients of 7s and 11S, are characterized by high levels of arginine, glutamine and asparagine, which provide a source of nitrogen for the developing seedling [2].The albumins are a more diverse group of proteins, usually soluble in water, with sedimentation coefficients of approximately 2s and some are rich in cysteine. While some 2s proteins appear to have only a storage function, some others such as lectins and protease and a-amylase inhibitors have biological activity. As a consequence of this these proteins are nutritionally undesirable. The sequences of a number of 2s seed storage proteins from different plants have shown that some of these proteins share sequence similarities and they have been grouped into a 2s superfamily of related sulfur- (EC 3.4.21.19).Note. The novel nucleotide sequence data published here have been deposited with the EMBL sequence data bank and are available under the accession number X56686. The novel amino acid sequence data have been deposited with the EMBL sequence data bank. rich seed proteins [3]. The 2s proteins from castor bean [4], rapeseed [5], mustard seed [6] Brazi...

Disulphide structure of a sunflower seed albumin: conserved and variant disulphide bonds in the cereal prolamin superfamily

“…SFA8 was purified from sunflower Hybrid 246 as described by [7] with an additional final separation by RP-HPLC on a SynChropak RP-P C18 Semi-preparative column (10X 250 ram) with a linear gradient (25% to 55%) of acetonitrile containing 0.07% (v/v) TFA in 0.05% (v/v) aqueous TFA. …”

“…However, post-translational proteolysis does not occur in sunflower, and the albumin fraction consists of monomeric proteins of Mr about 10000 18000 [5,6]. We have therefore determined the disulphide structure of one such sunflower albumin, a methionine-rich component SFA8 [7]. The pattern of disulphide bonds is identical to that in the heterodimeric conglutin 5 [8] and comparison with structures reported for members of the prolamin and inhibitor groups shows the presence of conserved and variant disulphide bonds in this superfamily of seed proteins.…”

Seed storage albumins: biosynthesis, trafficking and structures

“…The most common Nterminal residue for mature albumin subunits is proline, which effectively 'caps' the mature proteins. N-terminal prolines have been shown for the monomeric SFA8 (Kortt et al 1991) and both the small and large subunits of PawS1 and PawS2 (Mylne et al 2011). Another common N-terminal residue is pyro-Glu, which is caused by the side chain cyclisation of either glutamic acid or glutamine.…”

“…Not all albumins are cleaved into small and large subunits; e.g. the sunflower SFA8 albumin has been found to be a monomer in its mature form (Kortt et al 1991). Subsequent to the action of AEP, the activity of an aspartic exo-protease has been proposed to further process albumin by trimming the Cterminal regions of the cleaved propetides (Hiraiwa et al 1997).…”

Genetic contributions to agricultural sustainability

“…Sulphur-rich proteins that have been expressed in GM dicots include 2S seed albumins from sunflower, Brazil nut and sesame, proteins that contain up to 18% methionine residues (Altenbach et al 1989;Kortt et al 1991;Tai et al 1999a,b). This strategy has mainly been applied to the grain legumes owing to their low-intrinsic methionine concentrations; however, seeds of other species such as maize and canola have also been modified, not because they lack methionine themselves, but as a means of providing additional protein methionine in animal feed formulations containing grain legumes.…”