The Cytoplasm-Entry Domain of Antibacterial CdiA Is a Dynamic α-Helical Bundle with Disulfide-Dependent Structural Features

Publication date: Available online 8 June 2019Source: Journal of Molecular BiologyAuthor(s): Nicholas L. Bartelli, Sheng Sun, Grant C. Gucinski, Hongjun Zhou, Kiho Song, Christopher S. Hayes, Frederick W. DahlquistAbstractMany Gram-negative bacterial species use contact-dependent growth inhibition (CDI) systems to compete with neighboring cells. CDI+ strains express cell-surface CdiA effector proteins, which carry a toxic C-terminal region (CdiA-CT) that is cleaved from the effector upon transfer into the periplasm of target bacteria. The released CdiA-CT consists of two domains. The C-terminal domain is typically a nuclease that inhibits cell growth, and the N-terminal “cytoplasm-entry” domain mediates toxin translocation into the target-cell cytosol. Here, we use nuclear magnetic resonance and circular dichroism spectroscopic approaches to probe the structure, stability and dynamics of the cytoplasm-entry domain from Escherichia coli STEC_MHI813. Chemical shift analysis reveals that the CdiA-CTMHI813 entry domain is composed of a C-terminal helical bundle and a dynamic N-terminal region containing two disulfide linkages. Disruption of the disulfides by mutagenesis or chemical reduction destabilizes secondary structure over the N-terminus, but has no effect on the C-terminal helices. Though critical for N-terminal structure, the disulfides have only modest effects on global thermodynamic stability, and the entry domain exhibits characteristics of a molten globule. We fin...
Source: Journal of Molecular Biology - Category: Molecular Biology Source Type: research