TolB, N-terminal <p>TolB is a periplasmic protein from <taxon tax_id="562">Escherichia coli</taxon> that is part of the Tol-dependent translocation system involving group A and E colicins that is used to penetrate and kill cells [<cite idref="PUB00014149"/>, <cite idref="PUB00014150"/>]. TolB has two domains, an alpha-helical N-terminal domain that shares structural similarity with the C-terminal domain of transfer RNA ligases, and a beta-propeller C-terminal domain (<db_xref db="INTERPRO" dbkey="IPR011042"/>) that shares structural similarity with numerous members of the prolyl oligopeptidase family and, to a lesser extent, to class B metallo-beta-lactamases [<cite idref="PUB00014149"/>]. The function of the N-terminal domain is uncertain.</p>