This is the GASA gibberellin regulated cysteine rich protein (GRPs) family. The expression of these proteins is up-regulated by the plant hormone gibberellin, most of these proteins have a role in plant development and some of its members have antimicrobial activity [, ]. There are 12 cysteine residues conserved within the alignment giving the potential for these proteins to possess 6 disulphide bonds.Included in this family are some GRPs found in fruits and pollens that have been identified as allergens, including peach Pru p 7, Japanese apricot Pru m 7, orange Cit s 7, pomegranate Pun g 7, and cypress pollen GRP [, , ].
Members of this group are response regulators containing CheY-like receiver and HTH (helix-turn-helix) DNA-binding domains. Several members of this group have been characterised as response regulators controlling the genes involved in metabolism of citrate or C4-dicarboxylates (aspartate, fumarate, malate, and succinate). In Klebsiella pneumoniae, the phosphorylation of CitB, subsequent conformational changes and increase of apparent DNA-binding affinity (10 to 100-fold), and specific binding to the two sites in the citC-citS intergenic region have been shown experimentally []. The DcuS/R system in Escherichia coli is involved in C4-dicarboxylate-stimulated regulation of the genes encoding the anaerobic fumarate respiratory system []. The DpiB/A system (synonyms: CriR, CitB, but note that the name CitB can also be used for unrelated proteins) is involved in transcriptional regulation of the cit operon (citrate-specific fermentation genes) and of genes involved in plasmid inheritance [].Response regulators of the microbial two-component signal transduction systems typically consist of an N-terminal CheY-like receiver domain and a C-terminal output (usually DNA-binding) domain [, ]. In response to an environmental stimulus, a phosphoryl group is transferred from the His residue of sensor histidine kinase to an Asp residue in the CheY-like receiver domain of the cognate response regulator. Phosphorylation of the CheY-like receiver domain induces conformational changes that activate an associated output domain. Phosphorylation-induced conformational changes in the response regulator molecule have been demonstrated in direct structural studies []. In members of this group, these conformational changes affect the binding of the associated HTH domains to their recognition sites on the chromosomal DNA.HTH domains are very diverse with respect to their sequence, as well as the specific binding sites that they recognise [, , ]. There have been several attempts to classify them [, ]. A detailed sequence analysis of response regulator proteins has been hampered by the remarkable sequence conservation of their N-terminal CheY-like receiver domain, which largely masked (dis)similarities of the DNA-binding domains of various response regulators.For additional information please see [, ].
