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Conserved structural features anchor biofilm‐associated RTX –adhesins to the outer membrane of bacteria
Author(s) -
Guo Shuaiqi,
Langelaan David N.,
Phippen Sean W.,
Smith Steven P.,
Voets Ilja K.,
Davies Peter L.
Publication year - 2018
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/febs.14441
Subject(s) - periplasmic space , bacterial adhesin , bacterial outer membrane , chemistry , biophysics , bacteria , biofilm , cell wall , c terminus , protein structure , biochemistry , microbiology and biotechnology , biology , escherichia coli , gene , genetics , amino acid
Repeats‐in‐toxin ( RTX ) adhesins are present in many Gram‐negative bacteria to facilitate biofilm formation. Previously, we reported that the 1.5‐ MD a RTX adhesin ( Mp IBP ) from the Antarctic bacterium, Marinomonas primoryensis , is tethered to the bacterial cell surface via its N‐terminal Region I ( RI ). Here, we show the detailed structural features of RI . It has an N‐terminal periplasmic retention domain ( RIN ), a central domain ( RIM ) that can insert into the β‐barrel of an outer‐membrane pore protein during Mp IBP secretion, and three extracellular domains at its C terminus ( RIC ) that transition the protein into the extender region ( RII ). RIN has a novel β‐sandwich fold with a similar shape to βγ‐crystallins and tryptophan RNA attenuation proteins. Because RIM undergoes fast and extensive degradation in vitro , its narrow cylindrical shape was rapidly measured by small‐angle X‐ray scattering before proteolysis could occur. The crystal structure of RIC comprises three tandem β‐sandwich domains similar to those in RII , but increasing in their hydrophobicity with proximity to the outer membrane. In addition, the key Ca 2+ ion that rigidifies the linkers between RII domains is not present between the first two of these RIC domains. This more flexible RI linker near the cell surface can act as a ‘pivot’ to help the 0.6‐μm‐long Mp IBP sweep over larger volumes to find its binding partners. Since the physical features of RI are well conserved in the RTX adhesins of many Gram‐negative bacteria, our detailed structural and bioinformatic analyses serve as a model for investigating the surface retention of biofilm‐forming bacteria, including human pathogens.