Fig. 4.
Catalytic activity of the transglycosylase SLT domain of MltE is required for rdar morphotype expression. (A) Morphotypes of UMR1 ΔmltE ΔmltC overexpressing pMltE or pMltEE64Q. MltE expressed from a plasmid leads to an upregulation of the morphotype compared to that of strain UMR1 ΔmltE ΔmltC, while the expression of MltEE64Q showed a white and mucoid colony. VC, vector control pBad30. Strains were grown on Congo red agar plates for 24 h at 28°C. (B) Cell wall hydrolytic activity of lytic transglycosylases MltE and MltC. SLT domains from MltE and MltC were partially purified and resolved on SDS-PAGE gel containing M. luteus cells as substrates for lytic transglycosylase activity. The lytic transglycosylase activity of MltE was higher than the activity of MltC. The MltE and MltC proteins containing mutations in the conserved glutamyl residues show only residual hydrolytic activity. (C) An SDS-PAGE gel stained with Coomassie blue as a loading control. Lanes: 1, MltE; 2, MltEE64Q; 3, MltC; 4, MltCE219Q; and 5, molecular mass standard (in kDa).