Surprisingly, the MglAT78D modification, which perfects the overall consensus with all other GTPases (outside of the MglA group), abolished the activity of MglA, even though MglA protein was produced (Figure 9D) and yielded a localization pattern similar to the WT (as previously shown in Figure 3A). The T78D mutant had an even, smooth border (Figure 9C) and was unable to swarm (Figure 9B). Additionally, motility on 1.5% agarose and in MC was completely abolished (Table 1). Figure 9 Mutations in T78 demonstrate the requirement of a novel
PM3 substitution. This panel shows the phenotypes of strains MxH2247 (T78A), MxH2432 (T78D) and MxH2248 (T78S). See Figure 2 legend. Other substitutions at Thr78 had less severe effects. The motility defect of a ΔmglBA strain was complemented only poorly by the AZD8931 mouse mglAT78A allele, which also makes MglA protein (Figure 9D). Although small flares, suggestive of S-motility, were present at the edges of colonies formed by strain MxH2247 (Figure 9C), the swarming rates were very low
(Figure 9B). Isolated cells characteristic of A-motility were not seen at the edges of MxH2247 colonies although some movement was observed by videomicroscopy on 1.5% agarose (0.7 ± 1.1 μm/min). Gliding in MC (3.0 ± 1.4 μm/min) was only marginally better than the Δmgl parent. A conservative threonine to serine substitution yielded stable, functional MglA. As shown in Figure 8C, the edge morphology of MxH2248 (MglAT78S) was indistinguishable from the WT. Swarming of the T78S mutant was 100% of the control strain on a 1.5% selleck screening library agar but only 26% of the control on 0.3% agar suggesting that S-motility is impaired specifically in this mutant (Figure 9B). Consistent with this, videomicroscopy showed that the T78S mutant restored gliding speeds to 66% of the control on agarose (A-motility) but gliding rates on MC were only 56% of the control. Some mglA mutants impart a dominant negative phenotype Mutations in mglA that alter residues critical for protein interaction might have a dominant effect on motility and
can be useful tools to identify protein partners and mafosfamide suppressors. To identify such residues and determine the phenotype of mutant forms of MglA in the presence of WT MglA, we constructed merodiploid strains. Mutant alleles of mglA with normal mglB and the mgl regulatory buy Ro 61-8048 region were integrated at the chromosomal site of DK1622 (mglB + A + ), resulting in two tandem copies of mglB and mglA each expressed from the mgl promoter. Two additional controls were included in these assays to examine the effect of multiple copies of mglB and mglA on motility. One strain (MxH2375) contained two WT copies of mglBA and one strain (MxH2391) contained an additional copy of mglB, to simulate the effects of a merodiploid that carries an allele of mglA that fails to produce stable MglA protein, but produces extra MglB.