Several cDNAs related to an ABA-induced cDNA from barley aleurone were isolated from barley and corn seedlings that were undergoing dehydration. Four different barley polypeptides with sizes of 22.6, 16.2, 14.4 and 14.2 kDa and a single corn polypeptide with a size of 17.0 kDa were predicted from the nucleotide sequences of the cDNAs. These dehydration-induced proteins (dehydrins) are very similar to each other and to a previously identified rice protein induced by ABA and salt, and have at least some similarity to a previously identified cotton embryo protein. Each dehydrin is extremely hydrophilic, glycine-rich, cysteine- and tryptophan-free and contains repeated units in a conserved linear order. A lysine-rich repeating unit occurs twice in each protein, once at the carboxy terminus and once partway through the polypeptide, adjacent to a succession of serines. This repeating unit and the adjacent flanking run of serines are conserved with minimal variation among all dehydrins. Another repeating unit is flanked by the two copies of the lysine-rich unit, and varies in number from one to five copies. This latter repeating unit is less conserved than the former, varying even within a singly dehydrin. The messenger RNAs corresponding to each cDNA are abundant in dehydrating, but not in well-watered seedlings. The amino acid sequence of tryptic peptides from purified dehydration-induced proteins of corn established that the corn cDNAs correspond to a protein that is produced in abundance during the response of corn seedlings to dehydration.

Crystallographic studies of neuraminidase-sialic acid complexes indicate that sialic acid is distorted on binding the enzyme. Three arginine residues on the enzyme interact with the carboxylate group of the sugar which is observed to be equatorial to the saccharide ring as a consequence of its distorted geometry. The glycosidic oxygen is positioned within hydrogen-bonding distance of Asp-151, implicating this residue in catalysis.

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Single-chain variable fragments (scFvs) of anti-neuraminidase antibody NC10 were constructed by joining the VH and VL domains with 10-residue (Gly4Ser)2 and five-residue (Gly4Ser) linkers; a zero-residue linker scFv was constructed by joining the C-terminal residue of the VH domain to the N-terminus of the VL domain. The scFv with the 10- and five-residue linkers exclusively formed dimeric antibody fragments (M(r) 52000). These were shown to be bivalent and were able to cross-link two neuraminidase tetramers to form a 'sandwich' type complex; each antigen combining site could also bind an anti-idiotype Fab'. The zero-residue linker scFv (M(r) 70000) was shown to form a trimer with three active antigen combining sites, each binding an anti-idiotype Fab' to yield a complex of M(r) 212000. The orientation of the combining sites in the zero-residue linker scFv, however, was such that it could not cross-link tetramers of neuraminidase. BIAcore biosensor experiments showed that the affinity of each individual antigen combining site in both the 10- and five-residue linker scFv dimers and zero-residue linker scFv trimer was essentially the same when the scFvs were immobilized onto the sensor surface. However, when the scFvs were used as the analyte, the dimeric and trimeric scFvs showed an apparent increase in binding affinity due to the avidity of binding the multivalent scFvs.

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...

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