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Ronnie Willaert

Publications and source records attributed to Ronnie Willaert.

4 recordsLinked to original sources
PubMed2006

Ss-LrpB from Sulfolobus solfataricus condenses about 100 base pairs of its own operator DNA into globular nucleoprotein complexes.

Ss-LrpB from the hyperthermoacidophilic crenarchaeote Sulfolobus solfataricus P2 is a member of the Lrp-like family of Bacterial/Archaeal transcription regulators that binds its own control region at three regularly spaced and partially conserved 15-bp-long imperfect palindromes. We have used atomic force microscopy to analyze the architecture of Ss-LrpB.DNA complexes with a different stoichiometry formed with the wild type operator and with an operator mutant. Binding of dimeric Ss-LrpB to all three target sites is accompanied by the formation of globular complexes, in which the protein induces strong DNA deformations. Furthermore, DNA contour length foreshortening of these complexes indicates DNA wrapping, with about 100 bp being condensed. The average bending angle is 260 degrees . The establishment of protein-protein contacts between Ss-LrpB dimers in these globular complexes will contribute to the cooperativity of the binding. The profound remodeling of the control region is expected to have a strong impact on gene expression and might constitute the key element in the autoregulatory process.

DNA, Archaeal↗
PubMed2005

Continuous production of L(+)-tartaric acid from cis-epoxysuccinate using a membrane recycle reactor.

The one-step bioconversion of cis-epoxysuccinate (CES) to L(+)-tartaric acid by dried Rhodococcus rhodochrous cells containing CES hydrolase activity was studied by using a continuous bioconversion process. The influence of the pH and the temperature was assessed. A mathematical model was used to quantify the CES hydrolase activity and stability. The optimal pH, which resulted in a maximal CES hydrolase activity and stability, was pH 8.0. A large increase in stability (half-life time) could be obtained when the temperature was decreased from 37 to 14 degrees C during the continuous bioconversion. A total bioconversion was maintained for more than 100 days. This resulted in a large value for the specific productivity since the effect of the large increase in stability was much more important than the decrease of activity at the lower temperature. This continuous bioconversion process was further optimised by calculating the productivity for several continuously stirred tank reactors in series. The specific productivity could be nearly doubled when the number of reactors in the series was increased from 1 to 4.

Bioreactors↗
PubMed2005

Protein crystallization in hydrogel beads.

The use of hydrogel beads for the crystallization of proteins is explored in this contribution. The dynamic behaviour of the internal precipitant, protein concentration and relative supersaturation in a gel bead upon submerging the bead in a precipitant solution is characterized theoretically using a transient diffusion model. Agarose and calcium alginate beads have been used for the crystallization of a low-molecular-weight (14.4 kDa, hen egg-white lysozyme) and a high-molecular-weight (636.0 kDa, alcohol oxidase) protein. Entrapment of the protein in the agarose-gel matrix was accomplished using two methods. In the first method, a protein solution is mixed with the agarose sol solution. Gel beads are produced by immersing drops of the protein-agarose sol mixture in a cold paraffin solution. In the second method (which was used to produce calcium alginate and agarose beads), empty gel beads are first produced and subsequently filled with protein by diffusion from a bulk solution into the bead. This latter method has the advantage that a supplementary purification step is introduced (for protein aggregates and large impurities) owing to the diffusion process in the gel matrix. Increasing the precipitant, gel concentration and protein loading resulted in a larger number of crystals of smaller size. Consequently, agarose as well as alginate gels act as nucleation promoters. The supersaturation in a gel bead can be dynamically controlled by changing the precipitant and/or the protein concentration in the bulk solution. Manipulation of the supersaturation allowed the nucleation rate to be varied and led to the production of large crystals which were homogeneously distributed in the gel bead.

Alginates↗