Streptococcus suis DivIVA Protein Is a Substrate of Ser/Thr Kinase STK and Involved in Cell Division Regulation.

Hua Ni,Zhu-Qing Shao,Feng Zheng,Weiwei Fan,Xiangrong Cao,Hongfen Hou,Changjun Wang,Chaolong Li,Dan Hu,Qianqian Wu,Xuhui Zhu,Xiuzhen Pan

doi:10.3389/fcimb.2018.00085

Abstract

Streptococcus suis serotype 2 is an important swine pathogen and an emerging zoonotic agent that causes severe infections. Recent studies have reported a eukaryotic-like Ser/Thr protein kinase (STK) gene and characterized its role in the growth and virulence of different S. suis 2 strains. In the present study, phosphoproteomic analysis was adopted to identify substrates of the STK protein. Seven proteins that were annotated to participate in different cell processes were identified as potential substrates, which suggests the pleiotropic effects of stk on S. suis 2 by targeting multiple pathways. Among them, a protein characterized as cell division initiation protein (DivIVA) was further investigated. In vitro analysis demonstrated that the recombinant STK protein directly phosphorylates threonine at amino acid position 199 (Thr-199) of DivIVA. This effect could be completely abolished by the T199A mutation. To determine the specific role of DivIVA in growth and division, a divIVA mutant was constructed. The ΔdivIVA strain exhibited impaired growth and division, including lower viability, enlarged cell mass, asymmetrical division caused by aberrant septum, and extremely weak pathogenicity in a mouse infection model. Collectively, our results reveal that STK regulates the cell growth and virulence of S. suis 2 by targeting substrates that are involved in different biological pathways. The inactivation of DivIVA leads to severe defects in cell division and strongly attenuates pathogenicity, thereby indicating its potential as a molecular drug target against S. suis.

Highlights

Streptococcus suis (S. suis) is an important swine pathogen that causes a wide range of diseases, including arthritis, endocarditis, meningitis, pneumonia, and septicemia (Staats et al, 1997)
S. suis 2 Ser/Thr protein kinase (STK) Substrates Are Involved in Different Biological Processes of the Bacterium eukaryotelike STK (eSTK) regulates various cellular processes in bacteria, including cell growth and division, metabolism, stress response, and virulence
The results from the present and two previous studies (Zhu et al, 2014; Zhang et al, 2017) suggest that numerous biological activities of the stk mutants of S. suis 2 are affected to different extents such as delayed growth rate, abnormal cell division, sensitivity to oxidative stress, and attenuated virulence

Summary

Introduction

Streptococcus suis (S. suis) is an important swine pathogen that causes a wide range of diseases, including arthritis, endocarditis, meningitis, pneumonia, and septicemia (Staats et al, 1997). Recent genetic studies have suggested that serotypes 20, 22, 26, 32, 33, and Characterization of Streptococcus suis DivIVA. Among the remaining serotypes, S. suis 2 is considered to be the most virulent and it is frequently isolated from clinically diseased piglets (Lun et al, 2007). S. suis 2 caused two large outbreaks of human infection in China, which resulted in 38 deaths out of 204 reported cases and 14 deaths out of 25 cases in 2005 and 1998, respectively (Tang et al, 2006). The expression levels of these virulence factors are affected by a series of important transcription factors, various two-component signal transduction (TCS) systems and orphan regulators (Li et al, 2008, 2011; Pan et al, 2009; Aranda et al, 2010; Fulde et al, 2011; Willenborg et al, 2011; Zheng et al, 2011; Tang et al, 2012; Wang et al, 2012)

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