Item

Abstract

Yersinia pestis secretes a bacterial protein toxin named pesticin (Pst) that kills related bacteria of the same ecological niche by cleaving the murein (peptidoglycan). In order to get to the target in the periplasm the activity domain (A domain) of Pst (lysozyme) is equipped with a receptor domain (R domain) through which it binds specifically to the FyuA receptor protein at the surface of sensitive cells and a translocation domain (T domain) for translocation across the outer membrane. The R and T domain sequences and crystal structures are unique and reflect the specific import mechanism. In contrasts, the crystal structure of the A domain strongly resembles the crystal structure of phage T4 lysozyme (e gene product) despite of only 13% sequence identity. Replacement of the A domain by T4 lysozyme results in a toxic protein in which T4 lysozyme is carried by the pesticin R and T domains into the periplasm. The protein unfolds to enter the periplasm from outside cells and from the cytoplasm of a deriivative with an added signal peptide. Cross-linking by introduced cystine bridges prevents uptake which is relieved by reduction. Mutations in the predicted active site inactivate Pst and show a similar but not identical reaction center to phage T4 lysozyme.