Structure of the aaa+ protease delivery protein sspB
In molecular biology the protein domain SspB refers to stringent starvation protein B which is a protein thought to act in concert with sspA in the regulation of several proteins during cell growth. The exact function of sspB remains to be fully elucidated.
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.
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