Latest revision as of 18:00, 27 October 2020

CesT T3SS substrate chaperone

CesF and CesT are chaperone proteins that facilitate effector protein secretion in E. coli type-III secretion system. CesF has been proven to be necessary for secretion of EspF, while CesT is essential for Tir and Map effector protein secretion. We try to incorporate those two chaperones into our system because it was omitted in the engineered E. coli T3SS system we are using.

IISER_Bhopal 2020

(Author: Priya Sharma)

CesT is a T3SS-specific multi-cargo chaperone found in E. coli[1] that interacts with multiple bacterial effectors. It was initially discovered as a chaperone of Tir (translocated intimin receptor). [2]
Carbon storage regulator A (CsrA) is a widely distributed post-transcriptional regulator of translation initiation that binds to mRNA in gram-negative bacteria. It was identified for its effects on carbon metabolism.
T3SS is involved in host cell sensing and post-attachment remodeling of gene expressions in enteropathogenic Escherichia coli (EPEC) and enterohemorrhagic Escherichia coli (EHEC)[2]. CesT senses the activation of the Type III Secretion System via the release and translocation of Tir, one of its substrates. [2] [3] It transduces this information to the trans-acting post-transcriptional regulatory factor CsrA through sequestration, hindering CsrA’s ability to act on and silence its target mRNA.[3] CsrA plays an important role in, among other events, E. coli’s central carbon metabolism, helping regulate the mode of carbon source utilisation. CesT, therefore, acts as a module that senses T3SS activity and modifies E. coli’s metabolic program in response.

Carbon storage regulator A / Ribosomal RNA small subunit methyltransferase A (CsrA/RsmA) proteins primarily bind to the sequence motif A(N)GGA in single-stranded mRNA in the vicinity of the Shine–Dalgarno (SD) sequence to repress translation. [4]

Ces T antagonizes the post-transcriptional regulator CsrA as it binds to a region overlapping with its mRNA binding site[2]. CesT competitively inhibits CsrA/mRNA interactions hence it can be used for regulating the expression of a specific mRNA in EPEC and EHEC. [2]

Figure 1: 3D structure of CesT (dimer)

Additionally, we codon optimized the existing sequence for expression in Escherichia coli (Part name: BBa_K3450019).

References

1. Thomas, N. A. et al. CesT is a multi-effector chaperone and recruitment factor required for the efficient type III secretion of both LEE- and non-LEE-encoded effectors of enteropathogenic Escherichia coli. 57, 1762–1779 (2005).
2. Ye, F., Yang, F., Yu, R. et al. Molecular basis of binding between the global post-transcriptional regulator CsrA and the T3SS chaperone CesT. Nat Commun 9, 1196 (2018).
3. Elbaz N, Socol Y, Katsowich N, Rosenshine I. 2019. Control of type III secretion system effector/chaperone ratio fosters pathogen adaptation to host-adherent lifestyle. mBio 10:e02074-19
4. Kulkarni, P. R., Jia, T., Kuehne, S. A., Kerkering, T. M., Morris, E. R., Searle, M. S., Heeb, S., Rao, J., & Kulkarni, R. V. (2014). A sequence-based approach for prediction of CsrA/RsmA targets in bacteria with experimental validation in Pseudomonas aeruginosa. Nucleic acids research, 42(11), 6811–6825. https://doi.org/10.1093/nar/gku309

Sequence and Features