Biomedical subjects

D-W Zhu

Publications and source records attributed to D-W Zhu.

3 recordsLinked to original sources

PubMed2006

Attempts to rationalize protein crystallization using relative crystallizability.

Protein crystal growth (PCG) remains the bottleneck of crystallography despite many decades of study. The nucleation zone in the two-dimensional-phase diagram has been used to evaluate the relative crystallizability of proteins, which is expressed as a percentage over the phase area delineated by experimental protein and precipitating agent concentration ranges. For protein-salts which are subject to a direct temperature effect on solubility, as represented by Egg Lysozyme, a decrease in temperature augments the nucleation zone percentage whereas for those with retrograde solubility as a function of temperature, for example fructose-1,6-bisphosphatase in the presence and absence of AMP, an increase in temperature can significantly enhance the relative crystallizability. These results have been confirmed by the number of "hits" using PEGs as precipitating agents in Sparse Matrix Screen experiments for different proteins and are in excellent agreement with the relative crystallizability. The relationship between solubility dependence, relative crystallizability and crystallization success, has been evidenced. Such crystallizability can become a guide to identify efficient crystallization regions, providing a rational approach to PCG and structural biology.

Adenosine Monophosphate↗

PubMed2006

Structural basis of the multispecificity demonstrated by 17beta-hydroxysteroid dehydrogenase types 1 and 5.

17Beta-hydroxysteroid dehydrogenases/ketosteroid reductases (17beta-HSDs/KSRs) catalyze the last step of sex steroid synthesis or the first step of their degradation, and are thus critical for many physiological processes. The multispecificity demonstrated by 17beta-HSDs is important for steroid metabolism in gonadal and peripheral tissues, and is a consequence of the architecture of their binding and catalytic sites. Structurally, most of the family members are short chain dehydrogenase-reductases (SDRs) except the type 5 enzyme, which is an aldo-keto reductase (AKR). 17Beta-HSD type 1, a representative of the SDR family, has been studied extensively since the 1950s. However, its structure was not determined until the 1990s. It has always been considered as estrogen specific, in accord with the narrow binding tunnel that has been structurally determined and has been found to be complementary to estrogens. A recent study revealed that, in spite of the enzyme's narrow binding tunnel, the pseudo-symmetry of C19 steroids leads to its alternative binding, resulting in the multispecificity of the enzyme. Expressed in ovary, breast and placenta, the enzyme catalyzes the formation of another estrogen A-diol from DHEA in addition to the biosynthesis of estradiol; it also inactivates the most active androgen DHT by both 17beta-hydroxysteroid oxidation and 3-ketosteroid reduction. Type 5 17beta-HSD (AKR1C3) differs significantly from the type 1 enzyme by possessing a spacious and flexible steroid-binding site. This is estimated to be about 960 or 470 A3 in ternary complex with testosterone or 4-dione, respectively, whereas the binding site volume of 17beta-HSD1 is only about 340 A3. This characteristic of the 17beta-HSD5 binding site permits the docking of various steroids in different orientations, which encompasses a wider range of activities from 20alpha-, 17beta- and 3alpha-HSD/KSR to prostaglandin 11-ketoreductase. The in vitro activities of the enzyme are significantly lower than the type 1 enzyme. In the ternary complex with testosterone, the steroid C3-C17 position is quasi-reversed as compared to the complex with 4-dione. The multi-specificity contributes significantly to steroid metabolism in peripheral tissues, due to the high levels of 17beta-HSD5 mRNA in both breast and prostate tissues.

17-Hydroxysteroid Dehydrogenases↗

PubMed2004

Protein crystal growth on board Shenzhou 3: a concerted effort improves crystal diffraction quality and facilitates structure determination.

The crystallization of 16 proteins was carried out using 60 wells on board Shenzhou 3 in 2002. Although the mission was only 7 days, careful and concerted planning at all stages made it possible to obtain crystals of improved quality compared to their ground controls for some of the proteins. Significantly improved resolutions were obtained from diffracted crystals of 4 proteins. A complete data set from a space crystal of the PEP carboxykinase yielded significantly higher resolution (1.46A vs. 1.87A), I/sigma (22.4 vs. 15.5), and a lower average temperature factor (29.2A(2) vs. 42.9A(2)) than the best ground-based control crystal. The 3-D structure of the enzyme is well improved with significant ligand density. It has been postulated that the reduced convection and absence of macromolecule sedimentation under microgravity have advantages/benefits for protein crystal growth. Improvements in experimental design for protein crystal growth in microgravity are ongoing.

Crystallization↗