Catalyzes the dephosphorylation of O-phospho-L-serine into L-serine, a step in the L-serine biosynthetic pathway (PubMed:25037224, PubMed:25521849). Exhibits high specificity for L-phosphoserine compared to substrates like L-phosphothreonine (5% relative activity) and L-phosphotyrosine (1.7% relative activity) (PubMed:25521849). In the host, induces significant cytoskeleton rearrangements through cofilin dephosphorylation and its subsequent activation, and affects the expression of genes that regulate actin dynamics. It specifically interacts with HSP90, HSP70 and HSP27 that block apoptotic pathways but not with other HSPs. Also interacts with GAPDH. It actively dephosphorylates MAP kinase p38 and NF-kappa B p65 (specifically at Ser-536) that play crucial roles in inflammatory and immune responses. This in turn leads to down-regulation of Interleukin 8, a chemotactic and inflammatory cytokine. Thus might help the pathogen to evade the host's immune response (PubMed:26984196). Exogenous addition of purified SerB2 protein to human THP-1 cells (that can be differentiated into macrophage-like cells) induces microtubule rearrangements; the phosphatase activity is co-related to the elicited rearrangements, while addition of the ACT-domains alone elicits no rearrangements (PubMed:25521849). H2O + O-phospho-L-serine = L-serine + phosphate H2O + O-phospho-D-serine = D-serine + phosphate H2O + O-phospho-L-seryl-[protein] = L-seryl-[protein] + phosphate H2O + O-phospho-L-threonyl-[protein] = L-threonyl-[protein] + phosphate Binds 1 Mg(2+) ion per subunit (By similarity). Can also use Mn(2+) (PubMed:25037224, PubMed:25521849). Clofazimine, a drug being evaluated for XDR and MDR tuberculosis, inhibits SerB2 phosphatase activity and reverses the various functional effects described above and interactions with host proteins (PubMed:26984196). Is inhibited by known PSP inhibitors such as chlorpromazine, DL-AP3 and sodium orthovanadate, but not by okadaic acid (PubMed:25037224, PubMed:25521849). By binding to the ACT domains, amino-acids have various effects on enzyme activity: L-serine and L-glycine act as inhibitors, whereas L-lysine, L-tyrosine and L-phenylalanine are activators (PubMed:25521849). High throughput screen has been performed to identify specific PSP inhibitors with activity against intracellular bacteria; the two best hits identified in this screen, clorobiocin and rosaniline, are bactericidal and kill bacteria in infected macrophages in a dose-dependent manner (PubMed:25037224). kcat is 8.83 min(-1) (PubMed:25037224). kcat is 25400 sec(-1) (PubMed:25521849). Optimum pH is 7.5 (PubMed:25037224, PubMed:25521849). Activity declines progressively before pH 7.5 and is almost abolished at 6.0 while at higher pH the enzyme remains active till pH 9.0 (PubMed:25521849). Optimum temperature is 37 degrees Celsius. Activity declines at higher temperatures and is completely abolished by 50 degrees Celsius. Amino-acid biosynthesis; L-serine biosynthesis; L-serine from 3-phospho-D-glycerate: step 3/3. Homodimer. The dimeric population shifts to a tetramer in the presence of L-serine, which inactivates the enzyme. Is secreted into the cytosol of infected macrophages and is found in bronchoalveolar lavage samples of tuberculosis patients. Co-localizes with host tubulin. Folds into three domains, i.e. two ACT domains occurring in tandem at the N-terminus followed by the classical phosphatase (PSP) domain. The PSP domain alone is capable of hydrolyzing L-phosphoserine, albeit with much reduced efficacy. The ACT domains are involved in amino acid binding and play an important role in modulating enzymatic activity. Transposon mutagenesis experiments have identified that SerB2 is essential for the pathogen's viability while SerB1 is not. Belongs to the HAD-like hydrolase superfamily. SerB family.