Regulation of Effector Delivery by Type III Secretion Chaperone Proteins in Erwinia amylovora.

Luisa F Castiblanco,George W Sundin,Lindsay R Triplett

doi:10.3389/fmicb.2018.00146

Luisa F Castiblanco, George W Sundin + Show 1 more

Open Access

https://doi.org/10.3389/fmicb.2018.00146

Copy DOI

Abstract

Type III secretion (TTS) chaperones are critical for the delivery of many effector proteins from Gram-negative bacterial pathogens into host cells, functioning in the stabilization and hierarchical delivery of the effectors to the type III secretion system (TTSS). The plant pathogen Erwinia amylovora secretes at least four TTS effector proteins: DspE, Eop1, Eop3, and Eop4. DspE specifically interacts with the TTS chaperone protein DspF, which stabilizes the effector protein in the cytoplasm and promotes its efficient translocation through the TTSS. However, the role of E. amylovora chaperones in regulating the delivery of other secreted effectors is unknown. In this study, we identified functional interactions between the effector proteins DspE, Eop1, and Eop3 with the TTS chaperones DspF, Esc1 and Esc3 in yeast. Using site-directed mutagenesis, secretion, and translocation assays, we demonstrated that the three TTS chaperones have additive roles for the secretion and translocation of DspE into plant cells whereas DspF negatively affects the translocation of Eop1 and Eop3. Collectively, these results indicate that TTS chaperone proteins exhibit a cooperative behavior to orchestrate the effector secretion and translocation dynamics in E. amylovora.

Highlights

The delivery of effector proteins via the type III secretion system (TTSS) is a critical step for pathogenesis of many Gram-negative bacteria (Büttner and He, 2009; Raymond et al, 2013; Galán et al, 2014)
In order to assess whether DspF, Esc1, and Esc3 interact with multiple TTS effector proteins in E. amylovora, we performed a series of yeast two hybrid analyses
We examined the roles of DspF and two other TTS chaperones, Esc1 and Esc3, for interactions with effector proteins, effects on secretion and translocation of effectors, and effects on bacterial pathogenicity

Summary

Introduction

The delivery of effector proteins via the type III secretion system (TTSS) is a critical step for pathogenesis of many Gram-negative bacteria (Büttner and He, 2009; Raymond et al, 2013; Galán et al, 2014). The translocation efficiency of many effector proteins depends on a physical association with cytoplasmic type III secretion (TTS) chaperone proteins (Luo et al, 2001; Parsot et al, 2003; Matsumoto and Young, 2009; Triplett et al, 2009). TTS chaperones are typically low molecular weight acidic proteins that remain within the bacterial cytoplasm and form dimeric or hexameric structures that bind to their target effectors (Thomas et al, 2012; Tsai et al, 2015). TTS chaperones are categorized into three groups: class I TTS chaperones bind to effector proteins, class II TTS chaperones bind to type III pore-forming (translocon) proteins, and class III TTS chaperones bind to needle proteins

Methods

Results

Conclusion