Steric clashes with bound OMP peptides activate the DegS stress-response protease.
Escherichia coli senses envelope stress using a signaling cascade initiated when DegS cleaves a transmembrane inhibitor of a transcriptional activator for response genes. Each subunit of the DegS trimer contains a protease domain and a PDZ domain. During stress, unassembled outer-membrane proteins (OMPs) accumulate in the periplasm and their C-terminal peptides activate DegS by binding to its PDZ domains. In the absence of stress, autoinhibitory interactions, mediated by the L3 loop, stabilize inactive DegS, but it is not known how this autoinhibition is reversed during activation. Here, we show that OMP peptides initiate a steric clash between the PDZ domain and the L3 loop that results in a structural rearrangement of the loop and breaking of autoinhibitory interactions. Many different L3-loop sequences are compatible with activation but those that relieve the steric clash reduce OMP activation dramatically. Our results provide a compelling molecular mechanism for allosteric activation of DegS by OMP-peptide binding.
Department of Biology and.
Anna K
AK
de Regt
Department of Biology and Howard Hughes Medical Institute, Massachusetts Institute of Technology, Cambridge, MA 02139.
Tania A
TA
Baker
Department of Biology and bobsauer@mit.edu.
Robert T
RT
Sauer
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry* / Q000378:metabolism*; D004789:Enzyme Activation; D004926:Escherichia coli / Q000201:enzymology*; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000378:metabolism*; D008954:Models, Biological; D008969:Molecular Sequence Data; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism*; D011485:Protein Binding; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D001616:beta-Galactosidase / Q000378:metabolism
D001425:Bacterial Outer Membrane Proteins; D029968:Escherichia coli Proteins; D050505:Mutant Proteins; D010455:Peptides; C489349:degS protein, Escherichia coli; D001616:beta-Galactosidase
allosteric regulation; outer-membrane proteins; regulated intracellular proteolysis; stress sensor