This short domain is found in one or two copies at the amino terminus of ClpA and ClpB proteins from bacteria and eukaryotes. The function of these domains is uncertain but they may form a protein binding site [1]. In many bacterial species, including E.coli, this region represents the N-terminus of one of the key components of the pathogenicity island complex that injects toxin from one bacterium into another [2,3].

1: Structure and activity of ClpB from Escherichia coli. Role of the amino-and -carboxyl-terminal domains. Barnett ME, Zolkiewska A, Zolkiewski M; J Biol Chem 2000;275:37565-37571. PMID:10982797

2: Hcp family proteins secreted via the type VI secretion system coordinately regulate Escherichia coli K1 interaction with human brain microvascular endothelial cells. Zhou Y, Tao J, Yu H, Ni J, Zeng L, Teng Q, Kim KS, Zhao GP, Guo X, Yao Y; Infect Immun. 2012;80:1243-1251. PMID:22184413

3: The rise of the Type VI secretion system. Filloux A; F1000Prime Rep. 2013;5:52. PMID:24381728