TitleStructural analyses of chaperone-substrate interactions in
Type III secretion systems
NameChen, Li (author), Kalodimos, Charalampos (chair), Levy, Ronald (internal member), Ebright, Richard (internal member), Economou, Anastassios (outside member), Rutgers University, Graduate School - New Brunswick,
SubjectChemistry and Chemical Biology,
DescriptionThe type III secretion system (TTSS) is used by many Gram-negative bacteria to inject virulence proteins across lipid membranes directly into the cytoplasm of eukaryotic host cells. Chaperones are important components of TTS systems wherein they assist
with the assembly and operation of the entire machinery. Generally, the absence of the
chaperone results in rapid degradation, aggregation or reduced secretion of its cognate substrates. CesAB has been identified as the chaperone of the translocator EspA in one of the best characterized type III translocon, the enteropathogenic Escherichia coli (EPEC).
CesAB maintains the stability of EspA in bacterial cytoplasm by forming stable complex with it. CesAB exists as a homodimer in solution and it undergoes a subunit exchange mechanism to bind to EspA. Our biophysical data have shown that CesAB is a partially folded homodimer in solution. The solution structure of CesAB homodimer was determined by nuclear
magnetic resonance (NMR) spectroscopy. Multidimensional heteronuclear NMR
experiments in combination with other biophysical techniques were used to accomplish
structure determination. Structural and dynamic NMR studies reveal that CesAB exists as a loosely packed, conformationally dynamic homodimer in solution, properties that set it apart from other chaperones. We have characterized the binding of chaperone CesAB to the substrate EspA, a process required for bacterial pathogenicity. The structure of CesAB homodimer provides atomic details of the subunit exchange mechanism to interact with EspA. CesAB adopts
an autoinhibited conformation to prevent self-aggregation and it is rapidly activated for
EspA binding by transiently exposing part of the binding site in a mechanism facilitated by packing defects at its homodimeric coiled-coil subunit interface. EspA uses structural mimicry to offset the “weak spots” in CesAB and induce folding of both proteins into the
stable heterodimeric complex. Our results present a novel regulatory mechanism in protein-protein interactions mediated by finely-tuned structural instability coupled with molecular mimicry. We show that this mechanism is shared by other chaperone-substrate systems.
NoteIncludes bibliographical references
Noteby Li Chen
CollectionGraduate School - New Brunswick Electronic Theses and Dissertations
Organization NameRutgers, The State University of New Jersey
RightsThe author owns the copyright to this work.