Structural and biochemical characterization of Staphylococcus aureus clumping factor B/ligand interactions

Clumping factor B (ClfB) from Staphylococcus aureus is a bifunctional protein that binds to human cytokeratin 10 (K10) and fibrinogen (Fg). ClfB has been implicated in S. aureus colonization of nasal epithelium and is therefore a key virulence factor. People colonized with S. aureus are at an increased risk for invasive staphylococcal disease. In this study, we have determined the crystal structures of the ligand-binding region of ClfB in an apo-form and in complex with human K10 and Fg α-chain-derived peptides, respectively. We have determined the structures of MSCRAMM binding to two ligands with different sequences in the same site showing the versatile nature of the ligand recognition mode of microbial surface components recognizing adhesive matrix molecules. Both ligands bind ClfB by parallel β-sheet complementation as observed for the clumping factor A·γ-chain peptide complex. The β-sheet complementation is shorter in the ClfB·Fg α-chain peptide complex. The structures show that several residues in ClfB are important for binding to both ligands, whereas others only make contact with one of the ligands. A common motif GSSGXG found in both ligands is part of the ClfB-binding site. This motif is found in many human proteins thus raising the possibility that ClfB recognizes additional ligands.     

Desynchronisation of Glycolytic Oscillations in Yeast Cell Populations

Glycolytic oscillations of intact yeast cells of the strain Saccharomyces carlsbergensis were investigated at both the levels of cell populations and of individual cells. Individual cells showed glycolytic oscillations even at very low cell densities (e.g. 1.010⁵ cells/ml). By contrast, the collective behaviour on the population level was cell density-dependent: at high cell densities it is oscillatory, but below the threshold density of 1.010⁶ cells/ml the collective dynamics becomes quiescent. We demonstrate that the transition in the collective dynamics is caused by the desynchronisation of the oscillations of individual cells. This is characteristic for a Kuramoto transition. Spatially resolved measurements at low cell densities revealed that even cells that adhere to their neighbours oscillated with their own, independent frequencies and phases.     

Structure and Polymorphism of Amyloid and Amyloid-Like Aggregates

Biochemistry (Moscow) - Amyloids are protein aggregates with the cross-β structure. The interest in amyloids is explained, on the one hand, by their role in the development of socially...     

5'-carbamoylphosphonyl-[6-3H]-AZT as a tool for studying metabolic transformations of the nonradioactive counterpart, an inhibitor of HIV replication

An effective synthesis of 5'-carbamoylphosphonyl-[6-3H]-AZT was developed from [6-3H]-AZT.For the synthesized compound, chemical and enzymatic stability were determined and its penetration across HL-60 cell membranes was studied.     

Natural Fiber Welded Electrode Yarns for Knittable Textile Supercapacitors

Natural fiber welded (NFW) yarns embedded with porous carbon ­materials are described for applications as electrodes in textile electrochemical capacitors. With this fabrication technique, many kinds of carbons can be embedded into cellulose based yarns and subsequently knitted into full ­fabrics on industrial knitting machines. Yarns welded with carbon and ­stainless steel have device capacitances as high as 37 mF cm^‐1, one of the highest reported values for carbon‐based yarns. The versatility of this ­technique to weld any commercially available cellulose yarn with any ­micro‐ or nanocarbon means properties can be tuned for specific applications. Most importantly, it is found that despite having full flexibility, increased strength, and good electrochemical performance, not all of the electrode yarns are ­suitable for knitting. Therefore, it is recommended that all works reporting on fiber/yarn capacitors for wearables attempt processing into full fabrics.     

VirE2-dependent pores for ssDNA transfer across artificial and cell membranes

The transfer of single-stranded (ss) T-DNA from soil bacteria of the genus Agrobacterium with the help of the VirE2 protein, which possibly mediates the delivery of ss-T-DNA across the cell membrane, was demonstrated earlier, but how VirE2 participates in ssDNA transfer across artificial and natural membranes is not known. Using computational methods, we reconstructed model structures composed of two and four VirE2 proteins and showed by the MOLE program the formation of pores with channel diameters of 1.2-1.6 and 1.4-4.6 nm in a model structure formed from two and four VirE2 molecules, respectively. Using light scattering, we recorded the size distribution for recombinant VirE2-dependent complexes in aqueous solutions and found that VirE2 in a buffer solution is present as a complex made up of two or more proteins. We revealed single, long-lived jumps in voltage-dependent membrane conductance during coincubation of planar black membranes with the VirE2 protein. On the addition of VirE2 and FAM-labeled oligonucleotides to HeLa cells, the fluorescence intensity for the cells increased by 56% as compared to that for cells incubated only with oligonucleotides.     

Regulation of Chaperone Effects on a Yeast Prion by Cochaperone Sgt2

Yeast prions, based on self-seeded highly ordered fibrous aggregates (amyloids), serve as a model for human amyloid diseases. Propagation of yeast prions depends on the balance between chaperones of the Hsp100 and Hsp70 families. The yeast prion [PSI⁺] can be eliminated by an excess of the chaperone Hsp104. This effect is reversed by an excess of the chaperone Hsp70-Ssa. Here we show that the actions of Hsp104 and Ssa on [PSI⁺] are modulated by the small glutamine-rich tetratricopeptide cochaperone Sgt2. Sgt2 is conserved from yeast to humans, has previously been implicated in the guided entry of tail-anchored proteins (GET) trafficking pathway, and is known to interact with Hsps, cytosolic Get proteins, and tail-anchored proteins. We demonstrate that Sgt2 increases the ability of excess Ssa to counteract [PSI⁺] curing by excess Hsp104. Deletion of SGT2 also restores trafficking of a tail-anchored protein in cells with a disrupted GET pathway. One region of Sgt2 interacts both with the prion domain of Sup35 and with tail-anchored proteins. Sgt2 levels are increased in response to the presence of a prion when major Hsps are not induced. Our data implicate Sgt2 as an amyloid “sensor” and a regulator of chaperone targeting to different types of aggregation-prone proteins.