β-lactam antibiotic binding sites in Streptococcus pneumoniae StkP kinase extracellular region / 中华微生物学和免疫学杂志

ABSTRACT

Objective:To analyze the binding ability of motifs in the serine/threonine kinase StkP extracellular region (EC-StkP) of Streptococcus pneumoniae to β-lactam antibiotics. Methods:Three motifs (SXXK) in the EC-StkP were mutated into AXXA, respectively or simultaneously. Four mutant plasmids (EC- stkp-AXXA1, EC- stkp-AXXA2, EC- stkp-AXXA3 and EC- stkp-AXXA4) were transfected into recipient cells for cloning and expression. SDS-PAGE combined with gel image analysis was used to detect the expression of the recombinant mutant proteins (EC-rStkP-AXXA1, EC-rStkP-AXXA2, EC-rStkP-AXXA3 and EC-rStkP-AXXA4). The expressed mutated proteins were extracted and purified by Ni-NTA affinity chromatography. The binding abilities of the mutant proteins to penicillin (PCN) and cefotaxime (CTX) were detected by isothermal titration calorimetry (ITC 200) and surface plasmon resonance (Biacore t200). Results:PCN and CTX could not bind to the expressed proteins with mutations in the first or the third motif (EC-rStkP-AXXA1, EC-rStkP-AXXA3, EC-rStkP-AXXA4). EC-rStkP-AXXA2 could weakly bind to CTX, but not to PCN.Conclusions:All three motifs in the EC-StkP of Streptococcus pneumoniae could bind to β-lactam antibiotics with the first and the third motifs being more important.