Supplementary Material for: Expression and Characterization of Serotype 2 Streptococcus suis Arginine Deiminase

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