This protein family includes two copies of a five residue motif is found in a number of bacterial proteins bearing similarity to the protein CpxP (Swiss:P32158). This is a periplasmic protein that aids in combating extracytoplasmic protein-mediated toxicity, and may also be involved in the response to alkaline pH [1]. Another member of this family, Spy (Swiss:P77754) is also a periplasmic protein that may be involved in the response to stress [2]. The homology between CpxP and Spy may indicate that these two proteins are functionally related [1].

1: CpxP, a stress-combative member of the Cpx regulon. Danese PN, Silhavy TJ; J Bacteriol 1998;180:831-839. PMID:9473036

2: A new periplasmic protein of Escherichia coli which is synthesized in spheroplasts but not in intact cells. Hagenmaier S, Stierhof YD, Henning U; J Bacteriol 1997;179:2073-2076. PMID:9068658

3: The crystal structure Escherichia coli Spy. Kwon E, Kim DY, Gross CA, Gross JD, Kim KK; Protein Sci. 2010; [Epub ahead of print] PMID:20799348