Plant seed storage proteins, whose principal function appears to be the majornitrogen source for the developing plant, can be classified, on the basis oftheir structure, into different families. 11S-type globulins are non-glycosylated proteins which form hexameric structures [, ]. Each of the subunits in the hexamer is itself composed of an acidic and a basic chain derived from a single precursor and linked by a disulphide bond. This structure is shown in the followingrepresentation.+-------------------------+| |xxxxxxxxxxxCxxxxxxxxxxxxxxxxxxxxxxNGxCxxxxxxxxxxxxxxxxxxxxxxx|------Acidic-subunit-------------||-----Basic-subunit------||-----------------About-480-to-500-residues-----------------|'C': conserved cysteine involved in a disulphide bond.Members of the 11-S family include pea and broad bean legumins, oil seed rapecruciferin, rice glutelins, cotton beta-globulins, soybean glycinins, pumpkin11-S globulin, oat globulin, sunflower helianthinin G3, etc.This family represents the precursor protein which is cleaved into the two chains. These proteins contain two β-barrel domains.This family is a member of the 'cupin' superfamily on thebasis of their conserved barrel domain ('cupa' is the Latin termfor a small barrel).
Pyridoxal-dependent decarboxylases that act on ornithine-, lysine-, arginine- and related substrates can be classified into different familieson the basis of sequence similarity [, ]. One of these families includeseukaryotic ornithine decarboxylase (ODC), which catalyses the transformation of ornithine into putrescine; prokaryotic diaminopimelic acid decarboxylase(DAPDC), which catalyses the conversion of diaminopimelic acid into lysine,the final step of lysine biosynthesis; Pseudomonas syringae pv. tabaciprotein, tabA, which is probably involved in tabtoxin biosynthesis andis similar to DAPDC; and bacterial and plant biosynthetic argininedecarboxylase (ADC), which catalyses the transformation of arginine into agmatine, the first step in putrescine synthesis from arginine.Although these proteins, which are known collectively as group IVdecarboxylases [], probably share a common evolutionary origin, theirlevels of sequence similarity are low, being confined to a few shortconserved regions.The tomato ADC gene contains an open reading frame encoding a polypeptideof 502 amino acids and a predicted molecular mass of ~55kDa []. The predicted amino acid sequence shares 47 and 38% identify with oat and Escherichia coli ADCs, respectively. Gel blot hybridisation experiments show that,in tomato, ADC is encoded by a single gene and is expressed as a transcriptof ~2.2 kb in the fruit pericarp and leaf tissues [].
This entry represents the WRKY domain superfamily.The WRKY domain is a 60 amino acid region that is defined by the conserved amino acid sequence WRKYGQK at its N-terminal end, together with a novel zinc-finger-like motif. The WRKY domain is found in one or two copies in a superfamily of plant transcription factors involved in the regulation of various physiological programs that are unique to plants, including pathogen defence, senescence, trichome development and the biosynthesis of secondary metabolites. The WRKY domain binds specifically to the DNA sequence motif (T)(T)TGAC(C/T), which is known as the W box. The invariant TGAC core of the W box is essential for function and WRKY binding []. Some proteins known to contain a WRKY domain include Arabidopsis thaliana ZAP1 (Zinc-dependent Activator Protein-1) and AtWRKY44/TTG2, a protein involved in trichome development and anthocyanin pigmentation; and wild oat ABF1-2, two proteins involved in the gibberelic acid-induced expression of the alpha-Amy2 gene.Structural studies indicate that this domain is a four-stranded β-sheet with a zinc binding pocket, forming a novel zinc and DNA binding structure []. The WRKYGQK residues correspond to the most N-terminal β-strand, which enables extensive hydrophobic interactions, contributing to the structural stability of the β-sheet.
Plant seed storage proteins, whose principal function appears to be the majornitrogen source for the developing plant, can be classified, on the basis oftheir structure, into different families. 11-S are non-glycosylated proteinswhich form hexameric structures [, ]. Each of the subunits in the hexamer isitself composed of an acidic and a basic chain derived from a single precursorand linked by a disulphide bond. This structure is shown in the followingrepresentation.+-------------------------+| |xxxxxxxxxxxCxxxxxxxxxxxxxxxxxxxxxxNGxCxxxxxxxxxxxxxxxxxxxxxxx|------Acidic-subunit-------------||-----Basic-subunit------||-----------------About-480-to-500-residues-----------------|'C': conserved cysteine involved in a disulphide bond.Members of the 11-S family include pea and broad bean legumins, oil seed rapecruciferin, rice glutelins, cotton beta-globulins, soybean glycinins, pumpkin11-S globulin, oat globulin, sunflower helianthinin G3, etc.This family represents the precursor protein which is cleaved into the two chains. These proteins contain two β-barrel domains.This family is a member of the 'cupin' superfamily on thebasis of their conserved barrel domain ('cupa' is the Latin termfor a small barrel).The signature pattern for this family includes the conserved cleavage site between the acidic and basic subunits (Asn-Gly) and a proximal cysteine residue which is involved in the inter-chain disulphide bond.
The WRKY domain is a 60 amino acid region that is defined by the conserved amino acid sequence WRKYGQK at its N-terminal end, together with a novel zinc-finger-like motif. The WRKY domain is found in one or two copies in a superfamily of plant transcription factors involved in the regulation of various physiological programs that are unique to plants, including pathogen defence, senescence, trichome development and the biosynthesis of secondary metabolites. The WRKY domain binds specifically to the DNA sequence motif (T)(T)TGAC(C/T), which is known as the W box. The invariant TGAC core of the W box is essential for function and WRKY binding []. Some proteins known to contain a WRKY domain include Arabidopsis thaliana ZAP1 (Zinc-dependent Activator Protein-1) and AtWRKY44/TTG2, a protein involved in trichome development and anthocyanin pigmentation; and wild oat ABF1-2, two proteins involved in the gibberelic acid-induced expression of the alpha-Amy2 gene.Structural studies indicate that this domain is a four-stranded β-sheet with a zinc binding pocket, forming a novel zinc and DNA binding structure []. The WRKYGQK residues correspond to the most N-terminal β-strand, which enables extensive hydrophobic interactions, contributing to the structural stability of the β-sheet.
