<p>The stress-response A/B barrel domain is found in a class of stress-responseproteins in plants. It is also found in some bacterial fructose-bisphosphate aldolase such as at the C terminus of a fructose 1,6-bisphosphate aldolase from Hydrogenophilus thermoluteolus (<db_xref db="SWISSPROT" dbkey="Q9ZA13"/>) [<cite idref="PUB00016501"/>]. <db_xref db="SWISSPROT" dbkey="Q93NG5"/> is found in the pA01 plasmid, which encodes genes for molybdopterin uptake and degradation of plant alkaloid nicotine.</p><p> The stress-response A/B barrel domain forms a very stable dimer. This dimerbelongs to the superfamily of dimeric alpha+beta barrels in which the twobeta-sheets form a beta-barrel. The two molecules in the dimer are related bya 2-fold axis parallel to helix H1 and beta-strands B3 and B4. C-terminal residues extending from the beta4 strand of each monomer wrap around and connect with the beta2 strand and alpha1 helix of the opposing monomer to form the dimer interface [<cite idref="PUB00031274"/>, <cite idref="PUB00022615"/>, <cite idref="PUB00031070"/>].The outer surface of the beta-sheets of the two molecules forms a beta-barrel-like structure defining a central pore.</p><p>The function of the stress-response A/B barrel domain is unknown [<cite idref="PUB00031274"/>, <cite idref="PUB00022615"/>, <cite idref="PUB00031070"/>], but it is upregulated in response to salt stress in <taxon tax_id="73824">Populus balsamifera</taxon> (balsam poplar) [<cite idref="PUB00016419"/>].</p>Some proteins known to contain a stress response A/B barrel domain are listedbelow:<p>- Arabidopsis thaliana At3g17210</p><p>- Arabidopsis thaliana At5g22580</p><p>-Populus tremula stable protein 1 (SP-1)(Populus species), a thermostable stress-responsive protein.</p><p>- Pseudomonas hydrogenothermophila fructose 1,6-bisphosphate aldolase (cbbA).</p><p> The structure of one of these proteins has been solved (<db_xref db="SWISSPROT" dbkey="Q9LUV2"/>) and the domain forms an alpha-beta barrel dimer [<cite idref="PUB00016433"/>].</p> Stress responsive alpha-beta barrel