Biomedical subjects

K Pieterse

Publications and source records attributed to K Pieterse.

5 recordsLinked to original sources

PubMed2007

Passive coping and psychological distress in women adhering to regular breast cancer surveillance.

Since 2000 the MRISC study evaluates the psychological consequences of regular breast cancer surveillance for women at increased risk for hereditary breast cancer. Coping style may influence these psychological consequences. In a cohort of 357 women at increased risk for hereditary breast cancer, the impact of coping styles on the course, divided into level and trend of psychological distress (general and breast cancer specific) was examined, around two consecutive surveillance appointments. With structural equation modelling we found passive coping to be associated with higher levels of both general and breast cancer specific distress. Seeking social support, expression of emotions and thinking comforting thoughts were associated with lower levels of psychological distress. Coping style was not associated with the trend of psychological distress around the two surveillance appointments. It is recommendable to take coping styles into account when counselling these high-risk women.

Adaptation, Psychological↗

PubMed2006

Coarse-grained transmembrane proteins: hydrophobic matching, aggregation, and their effect on fusion.

Molecular transport between organelles is predominantly governed by vesicle fission and fusion. Unlike experimental vesicles, the fused vesicles in molecular dynamics simulations do not become spherical readily, because the lipid and water distribution is inappropriate for the fused state and spontaneous amendment is slow. Here, we study the hypothesis that enhanced transport across the membrane of water, lipids, or both is required to produce spherical vesicles. This is done by adding several kinds of model proteins to fusing vesicles. The results show that equilibration of both water and lipid content is a requirement for spherical vesicles. In addition, the effect of these transmembrane proteins is studied in bilayers and vesicles, including investigations into hydrophobic matching and aggregation. Our simulations show that the level of aggregation does not only depend on hydrophobic mismatch, but also on protein shape. Additionally, one of the proteins promotes fusion by inducing pore formation. Incorporation of these proteins allows even flat membranes to fuse spontaneously. Moreover, we encountered a novel spontaneous vesicle enlargement mechanism we call the engulfing lobe, which may explain how lipids added to a vesicle solution are quickly incorporated into the inner monolayer.

Lipid Bilayers↗

PubMed2006

A detailed look at vesicle fusion.

Many different hypotheses on the molecular mechanisms of vesicle fusion exist. Because these mechanisms cannot be readily asserted experimentally, we address the problem by a coarse-grained molecular dynamics simulations study and compare the results with the results of other techniques. The simulations performed include the fusion of small and large vesicles and exocytosis, i.e., the fusion of small vesicles with flat bilayers. We demonstrate that the stalk, the initial contact between two fusing vesicles, is initiated by lipid tails that extend spontaneously. The stalk is revealed to be composed of the contacting monolayers only, yet without hydrophobic voids. Anisotropic and radial expansion of the stalk have been theorized; we show that stalk evolution can proceed via both pathways starting from similar setups and that water triggers the transition from elongated stalk to hemifusion diaphragm.

Exocytosis↗

PubMed2005

The bilayer-vesicle transition is entropy driven.

Self-assembled bilayer membranes have a remarkable inclination to form closed shells or vesicles. This bilayer-vesicle transition has been shown experimentally and by various kinds of computer simulation techniques. Here we study this transition using coarse-grained molecular dynamics. The advantage of this simulation technique is that it allows for a detailed analysis of the transition, such as changes of the internal energy. Generally it is assumed that the bilayer-vesicle transition is driven by minimization of the edge energy. However, our simulations, which include solvent particles, show an increase in the potential energy of the system during the transition, implicating that the transition is not energy but entropy driven.

Computer Simulation↗

PubMed2000

Ladderlike oligomers; intramolecular hydrogen bonding, push-pull character, and electron affinity.

Symmetrical 2,5-bis(2-aminophenyl)pyrazines have been synthesized by application of the Stille coupling strategy. These cotrimers feature three important properties, namely strong intramolecular hydrogen bonding, push-pull character, and high electron affinity. The presence of intramolecular hydrogen bonds has been confirmed by 1H NMR, IR spectroscopy, and single-crystal X-ray diffraction. The hydrogen bond strength can be increased by substituting the amino groups with stronger electron-withdrawing functionalities. Despite the anticipated enhanced pi-conjugation through planarization, a hypsochromic shift was observed in the UV/Vis spectra, explained by a decrease in push-pull character. The electron affinity of the cotrimers was deduced from the first reduction potentials measured by cyclic voltammetry and is related to the electron-withdrawing character of the amino substituents. The results obtained have been compared with those of the corresponding 4-aminophenyl analogues and show that intramolecular hydrogen bonds can be used to design polymers with enhanced pi conjugation as well as a high electron affinity.

Journal Article↗