Interactions between metabolic intermediates and beta-galactosidase from Escherichia coli

Highly active spore biocatalyst by self-assembly of co-expressed anchoring scaffoldin and multimeric enzyme

We report a spore-based biocatalysis platform capable of producing and self-assembling active multimeric enzymes on a spore surface with a high loading density. This was achieved by co-expressing both a spore surface-anchoring scaffoldin protein containing multiple cohesin domains and a dockerin-tagged enzyme of interest in the mother cell compartment during Bacillus subtilis sporulation. Using this method, tetrameric β-galactosidase was successfully displayed on the spore surface with a loading density of 1.4 × 10⁴ active enzymes per spore particle. The resulting spore biocatalysts exhibited high conversion rates of transgalactosylation in water/organic emulsions. With easy manufacture, enhanced thermostability, excellent reusability, and long-term storage stability at ambient temperature, this approach holds a great potential in a wide range of biocatalysis applications especially involving organic phases.

Protein isoaspartate methyltransferase is a multicopy suppressor of protein aggregation in Escherichia coli

We used preS2-S'-beta-galactosidase, a three-domain fusion protein that aggregates extensively at 43 degrees C in the cytoplasm of Escherichia coli, to search for multicopy suppressors of protein aggregation and inclusion body formation and took advantage of the known differential solubility of preS2-S'-beta-galactosidase at 37 and 43 degrees C to develop a selection procedure for the gene products that would prevent its aggregation in vivo at 43 degrees C. First, we demonstrate that the differential solubility of preS2-S'-beta-galactosidase results in a lactose-positive phenotype at 37 degrees C as opposed to a lactose-negative phenotype at 43 degrees C. We searched for multicopy suppressors of preS2-S'-beta-galactosidase aggregation by selecting pink lactose-positive colonies on a background of white lactose-negative colonies at 43 degrees C after transformation of bacteria with an E. coli gene bank. We discovered that protein isoaspartate methyltransferase (PIMT) is a multicopy suppressor of preS2-S'-beta-galactosidase aggregation at 43 degrees C. Overexpression of PIMT reduces the amount of preS2-S'-beta-galactosidase found in inclusion bodies at 43 degrees C and increases its amount in soluble fractions. It reduces the level of isoaspartate formation in preS2-S'-beta-galactosidase and increases its thermal stability in E. coli crude extracts without increasing the thermostability of a control protein, citrate synthase, in the same extracts. We could not detect any induction of the heat shock response resulting from PIMT overexpression, as judged from amounts of DnaK and GroEL, which were similar in the PIMT-overproducing and control strains. These results suggest that PIMT might be overburdened in some physiological conditions and that its overproduction may be beneficial in conditions in which protein aggregation occurs, for example, during biotechnological protein overproduction or in protein aggregation diseases.

Thermoprotection by glycine betaine and choline

Glycine betaine is mostly known as an osmoprotectant. It is involved in the osmotic adaptation of eukaryotic and bacterial cells, and accumulates up to 1 M inside cells subjected to an osmotic upshock. Since, like other osmolytes, it can act as a protein stabilizer, its thermoprotectant properties were investigated. In vitro, like protein chaperones such as DnaK, glycine betaine and choline protect citrate synthase against thermodenaturation, and stimulate its renaturation after urea denaturation. In vivo, the internal concentration of glycine betaine is neither increased nor decreased after heat shock (this contrasts with a massive increase after osmotic upshock). However, even in exponential-phase bacteria grown in usual minimal salts media, the internal glycine betaine concentration attains levels (around 50 mM) which can protect proteins against thermodenaturation in vitro. Furthermore, glycine betaine and choline restore the viability of a dnaK deletion mutant at 42 degrees C, suggesting that glycine betaine not only acts as a thermoprotectant in vitro, but also acts as a thermoprotectant for Escherichia coli cells in vivo.

Thermal inactivation and reactivation of an enzyme in vivo. Pantothenate hydrolase of Pseudomonas fluorescens

Thermal inactivation and reactivation of pantothenate hydrolase were studied in whole cells of Pseudomonas fluorescens. The enzyme is susceptible to thermal inactivation in whole cells at 37-40 degrees C, and is reactivated when the temperature is lowered again. Chloramphenicol does not prevent reactivation. The activation energy of enzyme inactivation in vivo is about 540kJ/mol. This activation energy is 220kJ/mol in vitro, but it is increased to 550-630kJ/mol by several metabolites, such as succinate, glyoxylate and oxalate. Generally, good carbon sources, causing rapid growth, protect the enzyme from thermal inactivation in vivo, and enable reactivation to occur at a fast rate. The enzyme is also inactivated below 35 degrees C, showing an activation energy of about 35kJ/mol. Good carbon sources prevent this inactivation as well, and cause slight reactivation. Glycine, although not utilized for growth, protects the enzyme well from this inactivation but not from inactivation at 37-40 degrees C, and prevents reactivation totally. From the activation energies of inactivation and the effects of the various carbon sources, it appears possible that changes in the concentrations of intracellular metabolites may be responsible for the changes in inactivation and reactivation.