Cloning of a wheat 15-kDa grain softness protein (GSP). GSP is a mixture of puroindoline-like polypeptides.
The wheat starch 15-kDa protein (called grain softness protein or GSP) consists of a major polypeptide and several minor polypeptides. An antiserum raised against GSP was used to screen a wheat cDNA library. A cDNA family encoding approximately 15-kDa proteins that included a heptapeptide sequence previously isolated from protease digests of GSP was identified. A partial cDNA was used in a prokaryotic expression system to produce a fusion protein which reacted strongly against the original anti-GSP serum. A new antiserum raised against the fusion protein produced a weak reaction against a 15-kDa polypeptide extracted from wheat seeds. The results suggest that the proteins encoded by the cDNA family form a minor component of the mixture of 15-kDa polypeptides defined as GSP. RNA complementary to the cDNAs could be extracted from both soft and hard wheat grains from about half-way through grain filling. The encoded proteins are novel members of the 2S superfamily of seed proteins, a diverse family of proteins which maintain a characteristic framework of cysteine residues. The deduced proteins show the highest similarity to the oat 16-kDa avenin and to wheat puroindoline (a lipid-binding 15-kDa protein from wheat). Review of previously published data shows that puroindoline is also closely related to the major polypeptide of GSP, suggesting that the lipid-binding properties of GSP polypeptides may influence grain softness.
Rahman
S
S
Grain Quality Research Laboratory, CSIRO Division of Plant Industry, North Ryde, Australia.
Jolly
C J
CJ
Skerritt
J H
JH
Wallosheck
A
A
D000595:Amino Acid Sequence; D001483:Base Sequence; D015152:Blotting, Northern; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D008969:Molecular Sequence Data; D005810:Multigene Family / Q000235:genetics; D010446:Peptide Fragments / Q000737:chemistry / Q000235:genetics / Q000276:immunology; D010940:Plant Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012639:Seeds / Q000737:chemistry / Q000235:genetics*; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012689:Sequence Homology, Nucleic Acid; D014908:Triticum / Q000737:chemistry / Q000235:genetics*
D018076:DNA, Complementary; C088852:GSP-1 protein, Triticum aestivum; D010446:Peptide Fragments; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; C082942:puroindoline protein, Triticum aestivum