Bacterial efflux pumps confer multidrug resistance by transporting diverse antibiotics from the cell. In Gram-negative bacteria, some of these pumps form multi-protein assemblies that span the cell envelope. Here, we report the near-atomic resolution cryoEM structures of the Escherichia coli AcrAB-TolC multidrug efflux pump in resting and drug transport states, revealing a quaternary structural switch that allosterically couples and synchronizes initial ligand binding with channel opening. Within the transport-activated state, the channel remains open even though the pump cycles through three distinct conformations. Collectively, our data provide a dynamic mechanism for the assembly and operation of the AcrAB-TolC pump.
Abstract Dihydropyridine receptor (DHPR), an L-type Ca 2+ channel complex, plays an essential role in muscle contraction, secretion, integration of synaptic input in neurons and synaptic transmission. The molecular architecture of DHPR complex remains elusive. Here we present a 15-Å resolution cryo-electron microscopy structure of the skeletal DHPR/L-type Ca 2+ channel complex. The DHPR has an asymmetrical main body joined by a hook-like extension. The main body is composed of a “trapezoid” and a “tetrahedroid”. Homologous crystal structure docking and site-specific antibody labelling revealed that the α1 and α2 subunits are located in the “trapezoid” and the β subunit is located in the “tetrahedroid”. This structure revealed the molecular architecture of a eukaryotic Ca 2+ channel complex. Furthermore, this structure provides structural insights into the key elements of DHPR involved in physical coupling with the RyR/Ca 2+ release channel and shed light onto the mechanism of excitation-contraction coupling.
Hepatitis B Virus core protein (HBc) has multiple roles in the viral lifecycle: viral assembly, compartment for reverse transcription, intracellular trafficking, and nuclear functions. HBc displays assembly polymorphism - it can assemble into icosahedral capsid and aberrant non-capsid structures. It has been hypothesized that the assembly polymorphism is due to allosteric conformational changes of HBc dimer, the smallest assembly unit, however, the mechanism governing the polymorphic assembly of the HBc dimer is still elusive. By using the experimental antiviral drug BAY 41-4109, we successfully transformed the HBc assembly from icosahedral capsid to helical tube. Structural analyses of HBc dimers from helical tubes, T = 4 icosahedral capsid, and sheet-like HBc ensemble revealed differences within the inter-dimer interface. Disruption of the HBc inter-dimer interface may likely promote the various assembly forms of HBc. Our work provides new structural insights into the HBV assembly mechanism and strategic guide for anti-HBV drug design.
Inositol 1,4,5-trisphosphate receptors (IP 3 Rs) initiate a diverse array of physiological responses by carefully orchestrating intracellular calcium (Ca 2+ ) signals in response to various external cues. Notably, IP 3 R channel activity is determined by several obligatory factors, including IP 3 , Ca 2+ , and ATP. The critical basic amino acid residues in the N-terminal IP 3 -binding core (IBC) region that facilitate IP 3 binding are well characterized. In contrast, the residues conferring regulation by Ca 2+ have yet to be ascertained. Using comparative structural analysis of Ca 2+ -binding sites identified in two main families of intracellular Ca 2+ -release channels, ryanodine receptors (RyRs) and IP 3 Rs, we identified putative acidic residues coordinating Ca 2+ in the cytosolic calcium sensor region in IP 3 Rs. We determined the consequences of substituting putative Ca 2+ binding, acidic residues in IP 3 R family members. We show that the agonist-induced Ca 2+ release, single-channel open probability (P 0 ), and Ca 2+ sensitivities are markedly altered when the negative charge on the conserved acidic side chain residues is neutralized. Remarkably, neutralizing the negatively charged side chain on two of the residues individually in the putative Ca 2+ -binding pocket shifted the Ca 2+ required to activate IP 3 R to higher concentrations, indicating that these residues likely are a component of the Ca 2+ activation site in IP 3 R. Taken together, our findings indicate that Ca 2+ binding to a well-conserved activation site is a common underlying mechanism resulting in increased channel activity shared by IP 3 Rs and RyRs.
Recently, a kind of turquoise associated mineral has appeared on the market, which is very similar to turquoise in appearance. The authors studied a relevant sample by means of conventional gemmological tests and the other methods including thin-section observation, electron probe analysis, X-ray powder diffraction, infrared spectroscopy, Raman spectroscopy and ultraviolet-visible analysis, etc.The results showed that the main mineral component of the sample is crandallite and goyazite, as well as a certain amount of turquoise, etc. The main colour of the sample is blue, partially bluish green, and the blue colour is uneven, mainly enriched as dots or lumps. It has cryptocrystalline texture with the density of 2.52 g/cm3, and its refractive index is about 1.62 (point measurement). The infrared spectra of crandallite-goyazite show the main absorption peaks at 3 585, 3 420, 3 140, 1 320, 1 116, 1 039 cm-1 and 604 cm-1, and the Raman spectra of crandallite-goyazite show the main peaks at 1 104, 1 034, 987, 612, 518, 257 cm-1 and 185 cm-1, which are different from those of turquoise. Since it is difficult to identify this kind of turquoise associated mineral, conventional gemmological tests, Fourier infrared spectrometer, Raman spectrometer, X-ray powder diffraction analysis and electron probe analysis should be ultilized comprehensively.
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