Members of this family function as activators of D-amino acid oxidase. This enzyme catalyzes the oxidative deamination of D-3,4-dihydroxyphenylalanine (D-DOPA) and D-serine - a precursor of dopamine and a participant in glutamatergic transmission, respectively []. Variation in the DAO activator gene have been associated with bipolar disorder and major depression [], although other studies have cast doubt on such a link [].
This entry represents the enzyme 5'-methylthioadenosine/S-adenosylhomocysteine nucleosidase, which acts on its two substrates at the same active site, from the Rhizobiales (alphaproteobacteria).This clade of sequences is sufficiently distinct from the characterised proteins [, ]which form as to cast some doubt on the accuracy of annotations based on sequence similarity alone. This enzyme is involved in the recycling of the components of S-adenosylmethionine after it has donated one of its two non-ribose sulphur ligands to an acceptor. In the case of 5'-methylthioadenosine this represents the first step of the methionine salvage pathway in bacteria [, ]. This enzyme is widely distributed in bacteria.
Escherichia coli stringent starvation protein B (SspB), is thought to enhance the specificity of degradation of tmRNA-tagged proteins by the ClpXP protease. The tmRNA tag, also known as ssrA, is an 11-aa peptide added to the C terminus of proteins stalled during translation, targets proteins for degradation by ClpXP and ClpAP. SspB is a cytoplasmic protein that specifically binds to residues 1-4 and 7 of the tag. Binding of SspB enhances degradation of tagged proteins by ClpX, and masks sequence elements important for ClpA interactions, inhibiting degradation by ClpA []. However, more recent work has cast doubt on the importance of SspB in wild-type cells []. SspB is encoded in an operon whose synthesis is stimulated by carbon, amino acid, and phosphate starvation. SspB may play a special role during nutrient stress, for example by ensuring rapid degradation of the products of stalled translation, without causing a global increase in degradation of all ClpXP substrates [].
Escherichia coli stringent starvation protein B (SspB), is thought to enhance the specificity of degradation of tmRNA-tagged proteins by the ClpXP protease. The tmRNA tag, also known as ssrA, is an 11-aa peptide added to the C terminus of proteins stalled during translation, targets proteins for degradation by ClpXP and ClpAP. SspB is a cytoplasmic protein that specifically binds to residues 1-4 and 7 of the tag. Binding of SspB enhances degradation of tagged proteins by ClpX, and masks sequence elements important for ClpA interactions, inhibiting degradation by ClpA []. However, more recent work has cast doubt on the importance of SspB in wild-type cells []. SspB is encoded in an operon whose synthesis is stimulated by carbon, amino acid, and phosphate starvation. SspB may play a special role during nutrient stress, for example by ensuring rapid degradation of the products of stalled translation, without causing a global increase in degradation of all ClpXP substrates [].The structure of SspB revealed an SH3-like topology, sharing some similarity with the Sm-like fold [].
