Effect of molecular anisotropy on the nucleation of lysozyme

The growth of protein crystals is preceded by an induction period during which the protein solution prepares itself for crystallization. We have measured the length of the induction period for lysozyme as a function of the temperature for a solution of 16.9 mg/mL at pH 4.5 with 5% NaCl as the precipitating agent. The results are described with classical nucleation theory. The number of molecules in the critical nucleus n* turns out to be quite small: n* = 3-9. Such a small aggregate can hardly be considered as crystalline, as is assumed in the classical theory. By taking into account the anisotropy of the interaction between lysozyme molecules, we show that small nuclei, with n <6, will have a linear, fiberlike structure. Larger nuclei have a more compact structure. The energy of small, linear nuclei smoothly joins the values for larger nuclei and large crystalline aggregates. The data measured for the induction time can be grouped into two regions, one with short and one with long induction times. The transition point is near 22 degreesC. This implies that the best starting point for crystallization of lysozyme under the conditions we used is at or just below this temperature. The transition point corresponds approximately to the change from linear to more compact nuclei

Monolaterol, the first configurationally assigned phenylphenalenone derivative with a stereogenic center at C-9, from Monochoria elata

Phytochemical analysis of the roots of Monochoria elata resulted in the structure elucidation of monolaterol, the first configurationally assigned phenylphenalenone-type natural product with a stereogenic center at the phenyl-bearing carbon, C-9, and f

Development of a Functional cis-Prolyl Bond Biomimetic and Mechanistic Implications for Nickel Superoxide Dismutase

During recent years several peptide-based Ni superoxide dismutase (NiSOD) models have been developed. These NiSOD models show an important structural difference compared to the native NiSOD enzyme, which could cause a completely different mechanism of superoxide dismutation. In the native enzyme the peptide bond between Leu4 and Pro5 is cis-configured, while the NiSOD models exhibit a trans-configured peptide bond between these two residues. To shed light on how the configuration of this single peptide bond influences the activity of the NiSOD model peptides, a new cis-prolyl bond surrogate was developed. As surrogate we chose a leucine/alanine-based disubstituted 1,2,3-triazole, which was incorporated into the NiSOD model peptide replacing residues Leu4 and Pro5. The yielded 1,5-disubstituted triazole nickel peptide exhibited high SOD activity, which was approximately the same activity as its parent trans-configured analogue. Hence, the conformation of the prolyl peptide bond apparently has of minor importance for the catalytic activity of the metallopeptides as postulated in literature. Furthermore, it is shown that the triazole metallopeptide is forming a stable cyanide adduct as a substrate analogue model complex

Solution Structure and Backbone Dynamics of the K18G/R82E Alicyclobacillus acidocaldarius Thioredoxin Mutant: A Molecular Analysis of Its Reduced Thermal Stability

No general strategy for thermostability has been yet established, because the extra stability of thermophiles appears to be the sum of different cumulative stabilizing interactions. In addition, the increase of conformational rigidity observed in many thermophilic proteins, which in some cases disappears when mesophilic and thermophilic proteins are compared at their respective physiological temperatures, suggests that evolutionary adaptation tends to maintain corresponding states with respect to conformational flexibility. In this study, we accomplished a structural analysis of the K18G/R82E Alicyclobacillus acidocaldarius thioredoxin (BacTrx) mutant, which has reduced heat resistance with respect to the thermostable wildtype. Furthermore, we have also achieved a detailed study, carried out at 25, 45, and 65 °C, of the backbone dynamics of both the BacTrx and its K18G/R82E mutant. Our findings clearly indicate that the insertion of the two mutations causes a loss of energetically favorable long-range interactions and renders the secondary structure elements of the double mutants more similar to those of the mesophilic Escherichia coli thioredoxin. Moreover, protein dynamics analysis shows that at room temperature the BacTrx, as well as the double mutant, are globally as rigid as the mesophilic thioredoxins; differently, at 65 °C, which is in the optimal growth temperature range of A. acidocaldarius, the wild-type retains its rigidity while the double mutant is characterized by a large increase of the amplitude of the internal motions. Finally, our research interestingly shows that fast motions on the pico- to nanosecond time scale are not detrimental to protein stability and provide an entropic stabilization of the native state. This study further confirms that protein thermostability is reached through diverse stabilizing interactions, which have the key role to maintain the structural folding stable and functional at the working temperature

Large-Scale Recombinant Production of the SARS-CoV-2 Proteome for High-Throughput and Structural Biology Applications

The highly infectious disease COVID-19 caused by the Betacoronavirus SARS-CoV-2 poses a severe threat to humanity and demands the redirection of scientific efforts and criteria to organized research projects. The international COVID19-NMR consortium seeks to provide such new approaches by gathering scientific expertise worldwide. In particular, making available viral proteins and RNAs will pave the way to understanding the SARS-CoV-2 molecular components in detail. The research in COVID19-NMR and the resources provided through the consortium are fully disclosed to accelerate access and exploitation. NMR investigations of the viral molecular components are designated to provide the essential basis for further work, including macromolecular interaction studies and high-throughput drug screening. Here, we present the extensive catalog of a holistic SARS-CoV-2 protein preparation approach based on the consortium’s collective efforts. We provide protocols for the large-scale production of more than 80% of all SARS-CoV-2 proteins or essential parts of them. Several of the proteins were produced in more than one laboratory, demonstrating the high interoperability between NMR groups worldwide. For the majority of proteins, we can produce isotope-labeled samples of HSQC-grade. Together with several NMR chemical shift assignments made publicly available on covid19-nmr.com, we here provide highly valuable resources for the production of SARS-CoV-2 proteins in isotope-labeled form