Biomedical subjects

Guangyu Zhu

Publications and source records attributed to Guangyu Zhu.

22 records · Page 2Linked to original sources

PubMed2003

Crystal structure of GGA2 VHS domain and its implication in plasticity in the ligand binding pocket.

Golgi-localized, gamma-ear-containing, ARF binding (GGA) proteins regulate intracellular vesicle transport by recognizing sorting signals on the cargo surface in the initial step of the budding process. The VHS (VPS27, Hrs, and STAM) domain of GGA binds with the signal peptides. Here, a crystal structure of the VHS domain of GGA2 is reported at 2.2 A resolution, which permits a direct comparison with that of homologous proteins, GGA1 and GGA3. Significant structural difference is present in the loop between helices 6 and 7, which forms part of the ligand binding pocket. Intrinsic fluorescence spectroscopic study indicates that this loop undergoes a conformational change upon ligand binding. Thus, the current structure suggests that a conformational change induced by ligand binding occurs in this part of the ligand pocket.

ADP-Ribosylation Factors↗

PubMed2002

High resolution crystal structures of human Rab5a and five mutants with substitutions in the catalytically important phosphate-binding loop.

GTPase domain crystal structures of Rab5a wild type and five variants with mutations in the phosphate-binding loop are reported here at resolutions up to 1.5 A. Of particular interest, the A30P mutant was crystallized in complexes with GDP, GDP+AlF(3), and authentic GTP, respectively. The other variant crystals were obtained in complexes with a non-hydrolyzable GTP analog, GppNHp. All structures were solved in the same crystal form, providing an unusual opportunity to compare structures of small GTPases with different catalytic rates. The A30P mutant exhibits dramatically reduced GTPase activity and forms a GTP-bound complex stable enough for crystallographic analysis. Importantly, the A30P structure with bound GDP plus AlF(3) has been solved in the absence of a GTPase-activating protein, and it may resemble that of a transition state intermediate. Conformational changes are observed between the GTP-bound form and the transition state intermediate, mainly in the switch II region containing the catalytic Gln(79) residue and independent of A30P mutation-induced local alterations in the P-loop. The structures suggest an important catalytic role for a P-loop backbone amide group, which is eliminated in the A30P mutant, and support the notion that the transition state of GTPase-mediated GTP hydrolysis is of considerable dissociative character.

Catalysis↗

PubMedDate not supplied

Enzyme-carrying polymeric nanofibers prepared via electrospinning for use as unique biocatalysts.

Improvement of catalytic efficiency of immobilized enzymes via materials engineering was demonstrated through the preparation of bioactive nanofibers. Bioactive polystyrene (PS) nanofibers with a typical diameter of 120 nm were prepared and examined for catalytic efficiency for biotransformations. The nanofibers were produced by electrospinning functionalized PS, followed by the chemical attachment of a model enzyme, alpha-chymotrypsin. The observed enzyme loading as determined by active site titration was up to 1.4% (wt/wt), corresponding to over 27.4% monolayer coverage of the external surface of nanofibers. The apparent hydrolytic activity of the nanofibrous enzyme in aqueous solutions was over 65% of that of the native enzyme, indicating a high catalytic efficiency as compared to other forms of immobilized enzymes. Furthermore, nanofibrous alpha-chymotrypsin exhibited a much-improved nonaqueous activity that was over 3 orders of magnitude higher than that of its native counterpart suspended in organic solvents including hexane and isooctane. It appeared that the covalent binding also improved the enzyme's stability against structural denaturation, such that the half-life of the nanofibrous enzyme in methanol was 18-fold longer than that of the native enzyme.

Animals↗

PubMedDate not supplied

Self-assembling of polymer-enzyme conjugates at oil/water interfaces.

Interface-binding enzymes are desirable for biphasic reactions in that they offer simultaneous access to substrates dissolved in both phases across the interface. It has been shown that conjugating water-soluble enzymes with hydrophobic polymers facilitated the assembling of enzymes at oil/water interfaces. In this work, the interfacial assembling of alpha-chymotrypsin conjugated with polystyrene, poly(methyl methacrylate), and poly(l-lactic acid) was examined using the pendant drop method. The interface-assembling process of the conjugates from the organic phase followed a similar pattern of that of native alpha-chymotrypsin from the aqueous buffer phase, i.e., the interfacial tension decreased gradually with time. However, when the conjugates were dispersed in the form of particulates in the aqueous phase, in which the conjugate was insoluble, the assembling occurred faster and the interfacial tension quickly approached zero. It was suspected that the assembling in this case involved two steps, i.e., the adsorption of the particulates and the subsequent rearrangement, dissociation, and redispersion of the conjugates at the interface. The effect of other factors, including the polarity of organic solvent and pH and ionic strength of the aqueous phase, was evaluated. It was found that the polar solvent slightly facilitated the assembling, whereas pH and ionic strength showed minimal effects.

Biochemistry↗