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

Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, Russian Federation.
FEBS Letters (Impact Factor: 3.58). 12/1996; 396(2-3):285-8. DOI: 10.1016/0014-5793(96)01117-9
Source: PubMed

ABSTRACT Disulphide mapping of a methionine-rich 2S albumin from sunflower seeds showed four intra-chain disulphide bonds which are homologous with those in a related heterodimeric albumin from lupin seeds (conglutin delta). Similar conserved disulphide bonds are also present in alpha-gliadin and gamma-gliadin storage proteins of wheat, but a lower level of conservation is present in a further related group of proteins, the cereal inhibitors of alpha-amylase and trypsin. These differences may relate to the different functions of the proteins.

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    ABSTRACT: Alignment of 98 S-rich prolamin amino acid sequences illustrated that four cysteines were preserved nearly 100% and four cysteines were less well conserved. These residues form two to four intramolecular disulfide bonds in several S-rich prolamins. For maize gamma zein, it is unknown whether the eight C-terminal cysteines form intramolecular disulfide bonds. If gamma zein contains intramolecular disulfide bonds, modifications of critical cysteines in soluble thioredoxin–gamma zein fusion protein might prevent disulfide bond formation and result in misfolded and insoluble protein in Escherichia coli. Individual modification of conserved cysteines C128 and C136 resulted in a four-fold reduction in solubility and a significant decrease in expression level compared to wild-type fusion protein. Modification of conserved C156 resulted in a two-fold reduction in expression level but not a significant change in solubility until combined with a non-deleterious Q181R modification. This suggested that C128 and C136 were involved in disulfide bonds critical for protein folding, whereas C156 was more critical for protein stability. Modification of a non-conserved N-terminal cysteine residue (C117) resulted in increased protein solubility, suggesting it was not involved in an intramolecular disulfide bond. From these data and a review of the literature, a disulfide map for gamma zein is proposed.
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