Expression and Characterization of Serotype 2 Streptococcus suis Arginine Deiminase

Abstract

Background: Arginine deiminase (ArcA) has been speculated to facilitate the intracellular survival of Streptococcus suis under acidic conditions. However, the physical and biological properties and function of SS2-ArcA have not yet been elucidated. Methods: Recombinant SS2-ArcA (rSS2-ArcA) was expressed and purified using Ni-NTA affinity chromatography. Under various pH and temperature conditions, the enzymatic properties of purified rSS2-ArcA and crude native SS2-ArcA were determined. Results: The SS2-arcA-deduced amino acid sequence contained a conserved catalytic triad (Cys399-His273-Glu218). The optimum temperature and pH of 47-kDa rSS2-ArcA and crude native SS2-ArcA were 42°C and pH 7.2. The rSS2-ArcA and crude native SS2-ArcA were stable for 3 h at 4 and 25°C, respectively. The pH stability and dependency tests suggested that rSS2-ArcA and crude native SS2-ArcA were functionally active in acidic conditions. The <smlcap>L</smlcap>-arginine substrate binding affinity (K_m) values of rSS2-ArcA (specific activity 16.00 U/mg) and crude native SS2-ArcA (specific activity 0.23 U/mg) were 0.058 and 0.157 m<smlcap>M</smlcap>, respectively. rSS2-ArcA exhibited a weak binding affinity with the common ArcA inhibitors <smlcap>L</smlcap>-canavanine and <smlcap>L</smlcap>-NIO. Furthermore, the partial inactivation of SS2-ArcA significantly impaired the viability and growth of SS2 at pH 4.0, 6.0, and 7.5. Conclusions: This study profoundly demonstrated the involvement of ArcA enzymatic activity in S. suis survival under acidic conditions.