5-fold in the Abiraterone solubility dmso I124L mutant compared with the wild-type MetA (Table 2). This finding is consistent with the slight increase in k cat/Km of 58% compared with the native enzyme. Thus, the stabilizing mutations had little to no effect on the catalytic activity of the MetA enzyme. Table 2 Kinetic parameters of the wild-type and stabilized
MetA enzymes Enzyme k cat (s-1) Succinyl-CoA L-homoserine K m (mM) k cat/K M (M-1 s-1) K m (mM) k cat/K M (M-1 s-1) MetA, wt 36.72 ± 0.9 0.37 ± 0.05 9.9*104 1.25 ± 0.3 2.93*104 I124L 38.59 ± 0.5 0.38 ± 0.06 1.02*105 0.83 ± 0.15 4.65*104 I229Y 39.28 ± 0.5 0.36 ± 0.06 1.09*105 1.42 ± 0.1 2.76*104 MetA mutant enzymes exhibit reduced aggregation at an elevated temperature (45°C) in vitro and in vivo Native MetA was previously reported to become completely aggregated in vitro at temperatures of 44°C and higher .
To examine the aggregation-prone behavior of native and stabilized MetAs, we generated in vitro aggregates of the purified proteins as described in the Methods section. The native MetA enzyme was completely aggregated after heating at 45°C for 30 min (Figure 2). In contrast, the engineered I124L and I229Y mutant MetAs demonstrated a higher level of aggregation resistance; only 73% of I124L and 66% of I229Y were insoluble (Figure 2). Figure 2 Heat-induced aggregation of native and mutant MetAs in vitro . Aggregated GSK3235025 datasheet proteins were prepared through incubation at 45°C for 30 min as described in the Methods section; the soluble (black columns) and insoluble (gray columns) protein Farnesyltransferase fractions were separated by
centrifugation at 14,000 g for 30 min and analyzed through Western blotting with rabbit anti-MetA antibodies. The densitometric analysis of band intensity was conducted using WCIF Image J software. The total amount of MetAs before an incubation was equal to 1. The error bars represent the standard deviations of duplicate independent cultures. In addition, we examined the level of soluble MetA enzymes in vivo after heat shock at 45°C for 30 min (Additional file 4: Figure S3). The amount of the native MetA protein in the soluble fraction decreased to 52% following heat shock, whereas the relative amounts of soluble MetA I124L and I229Y mutants were 76% and 68%, respectively. The amount of insoluble native MetA protein increased 28-fold after heating, while those of stabilized MetA I124L and I229Y mutants increased 20- and 17-fold, respectively (Additional file 4: Figure S3). These results confirmed the higher resistance of the stabilized I124L and I229Y mutant enzymes to aggregation. MetA mutant enzymes are more stable in vivo at normal (37°C) and elevated (44°C) temperatures To determine the effects of these mutations on MetA stability in vivo, we analyzed the degradation of the mutant and native MetA enzymes after blocking protein synthesis using chloramphenicol.