European Biophysics Journal最新文献

Band-forming experiments allow the study of a wide variety of systems by overlaying two solutions with different densities in an analytical ultracentrifuge. Despite their potential benefits over other methods, these experiments are rarely used because all available fitting software encounters systematic errors, failing to account for the evolving gradient in density and viscosity due to diffusive mixing between the two layers. We develop and experimentally validate a predictive model for the purely diffusive mixing of two solutions in a cylindrical system. Capturing the space- and time-dependent evolution of density and viscosity in band-forming experiments, the model enhances their interpretation and underscores the need for analysis software to account for these dynamic changes.

Nucleic acids, molecules essential for all life, can adopt many alternative structures besides the well-known right-handed double helix, some of which have been reported to exist and function in vivo. One of the most appropriate methods for structural studies of nucleic acids is circular dichroism spectroscopy, utilizing structure-induced chirality due to the asymmetric winding of absorbing nucleobases. Using electronic CD and absorption spectroscopies in combination with melting experiments, we analyzed a conformational equilibrium between DNA double helix and two alternative conformations of nucleic acids, cytosine i-motifs and guanine quadruplexes, as a function of the primary structure of model G/C-rich sequences, containing blocks of G and C runs in particular DNA strands. This paper is a part of special issue dedicated to 70th anniversary of the Biophysical Institute of the Czech Academy of Sciences, where circular dichroism spectroscopy of nucleic acids has been used successfully and impactfully for many years.

The thiamine (vitamin B1) biosynthesis pathway is essential for most prokaryotes and some eukaryotes, including yeasts and plants. The 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate kinase (HMPP kinase), encoded by the thiD gene, catalyzes two phosphorylation reactions involving intermediates in this pathway, ultimately producing thiamine pyrophosphate, the active form of thiamine. Here, we present the crystal structure of HMPP kinase from Thermus thermophilus HB8 (TtHMPPK), resolved at a resolution of 2.05 Å. The asymmetric unit of the TtHMPPK structure includes one protomer, though it functions as a homodimer in its active form, like the HMPP kinase from Salmonella typhimurium. The TtHMPPK protomer is an α/β protein featuring nine β-sheets flanked by eight structurally conserved α-helices, which are characteristic of the ribokinase family. The structure reveals a Rossmann β–α–β motif, commonly found in nucleotide-binding proteins. Structural analysis of TtHMPPK, compared to the Salmonella typhimurium HMPP kinase, indicates that Ala16, Thr40, Gln42, Ala78, and Val105 are active site residues involved in catalysis. The structural studies suggest that TtHMPPK belongs to the ribokinase superfamily and exhibits structural similarities with an enzyme containing a Rossmann-like structural motif (RLM). This Rossmann fold enables HMPP kinase to catalyze the phosphorylation of HMPP, a critical step in thiamine production.

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Comparing experimental and calculated hydrodynamic properties of (bio)-macromolecules, such as the translational diffusion coefficient (D_{t(20,w)}^{0}) and the intrinsic viscosity [η], is a useful strategy for the validation of predicted and/or solved atomic-level structures. Bead modeling is a prominent methodology, with several computational tools available. The program GRPY (Generalized Rotne–Prager–Yamakawa) allows the hydrodynamic calculations to be performed at the one-atom one-bead scale, allowing overlaps, but it is computer intensive with CPU requirements depending on the number of beads N as ~ N³. The program ZENO, based on the electrostatics–hydrodynamics analogy and using a Monte Carlo numerical path integration, can compute (D_{t(20,w)}^{0}) and [η] directly on bead models, and it is almost independent of the target size. Since bead models are a very efficient way to include the hydration effect when dealing with bio-macromolecules, we present here an in-depth comparison between GRPY and ZENO, both as implemented in the US-SOMO suite. Relatively low but systematic differences (0.2–2%, increasing with model size) appear when using bead models of proteins at the residue- or atomic-level scales. When comparing the results provided on a restricted set of bead models by two other computationally intensive methods having other drawbacks, the very accurate but not handling overlaps HYDROMULTIPOLE, and the boundary elements BEST requiring extrapolation, GRPY was found to fare better than ZENO. While efforts are in progress to directly improve the ZENO performance, a heuristic correction based on the results for a series of protein bead models is proposed, allowing for a better consistency with GRPY.

Recombinant adeno-associated virus (rAAV) has been widely used as an effective delivery tool in gene therapy. One of the challenges facing the production of high-quality rAAV is optimization of the production and purification methodologies. Cesium chloride density gradient ultracentrifugation (CsCl-DGUC) has been traditionally utilized for rAAV purification; however, few studies have focused on CsCl-DGUC for rAAV purification despite this technique having a great potential for clinical-grade or large-scale rAAV production. In this study, we aimed to explore the unaddressed challenges associated with rAAV purification using CsCl-DGUC. We clarified that AAV capsids assembled by the different stoichiometries of three viral proteins (VP1, VP2, and VP3) showed heterogeneous population in the CsCl density gradient and encapsidated DNA increased the buoyant density differences of these capsids, resulting in the wider distribution. We implemented CsCl-DGUC using a vertical rotor which improved throughput and enhanced the separation of desired AAV particles from impurities. Furthermore, we examined the effect of CsCl exposure during purification, and the presence of residual CsCl in the purified rAAV. This study provides valuable insights into the application of CsCl-DGUC in the manufacturing of rAAV while ensuring adequate efficacy and safety for gene therapy.