Search

Chloride ion-pumping rhodopsin (ClR) in some marine bacteria utilizes light energy to actively transport Cl- into cells. How the ClR initiates the transport is elusive. Here, we show the dynamics of ion transport observed with time-resolved serial femtosecond (fs) crystallography using the Linac Coherent Light Source. X-ray pulses captured structural changes in ClR upon flash illumination with a 550 nm fs-pumping laser. High-resolution structures for five time points (dark to 100 ps after flashing) reveal complex and coordinated dynamics comprising retinal isomerization, water molecule rearrangement, and conformational changes of various residues. Combining data from time-resolved spectroscopy experiments and molecular dynamics simulations, this study reveals that the chloride ion close to the Schiff base undergoes a dissociation-diffusion process upon light-triggered retinal isomerization.

Macaque restricts hepatitis B virus (HBV) infection because its receptor homologue, NTCP (mNTCP), cannot bind preS1 on viral surface. To reveal how mNTCP loses the viral receptor function, we here solve the cryo-electron microscopy structure of mNTCP. Superposing on the human NTCP (hNTCP)-preS1 complex structure shows that Arg158 of mNTCP causes steric clash to prevent preS1 from embedding onto the bile acid tunnel of NTCP. Cell-based mutation analysis confirms that only Gly158 permitted preS1 binding, in contrast to robust bile acid transport among mutations. As the second determinant, Asn86 on the extracellular surface of mNTCP shows less capacity to restrain preS1 from dynamic fluctuation than Lys86 of hNTCP, resulting in unstable preS1 binding. Additionally, presence of long-chain conjugated-bile acids in the tunnel induces steric hindrance with preS1 through their tailed-chain. This study presents structural basis in which multiple sites in mNTCP constitute a molecular barrier to strictly restrict HBV. Here the authors look at why macaque is non-susceptible to hepatitis B virus by focusing on the protein structure of the host receptor homolog. They show that macaque-derived host receptor homolog has multiple structural defects against virus binding. [ABSTRACT FROM AUTHOR]

In eukaryotes, accurate chromosome segregation during mitosis and meiosis is coordinated by kinetochores, which are unique chromosomal sites for microtubule attachment (1,2). Centromeres specify the kinetochore formation sites on individual chromosomes, and are epigenetically marked by the assembly of nucleosomes containing the centromere-specific histone H3 variant, CENP-A (3-12). Although the underlying mechanism is unclear, centromere inheritance is probably dictated by the architecture of the centromeric nucleosome. Here we report the crystal structure of the human centromeric nucleosome containing CENP-A and its cognate α-satellite DNA derivative (147 base pairs). In the human CENP-A nucleosome, the DNA is wrapped around the histone octamer, consisting of two each of histones H2A, H2B, H4 and CENP-A, in a left-handed orientation. However, unlike the canonical H3 nucleosome, only the central 121 base pairs of the DNA are visible. The thirteen base pairs from both ends of the DNA are invisible in the crystal structure, and the αN helix of CENP-A is shorter than that of H3, which is known to be important for the orientation of the DNA ends in the canonical H3 nucleosome (13). A structural comparison of the CENP-A and H3 nucleosomes revealed that CENP-A contains two extra amino acid residues (Arg80 and Gly81) in the loop 1 region, which is completely exposed to the solvent. Mutations of the CENP-A loop 1 residues reduced CENP-A retention at the centromeres in human cells. Therefore, the CENP-A loop 1 may function in stabilizing the centromeric chromatin containing CENP-A, possibly by providing a binding site for trans-acting factors. The structure provides the first atomic-resolution picture of the centromere-specific nucleosome., Octasome and hemisome models have been proposed for the CENP-A nucleosome architecture (14). In the octasome model, two each of histones H2A, H2B, H4 and CENP-A form a histone octamer, [...]

We have characterized both wild-type and mutant TRAP (trp RNA-binding attenuation protein) from Bacillus stearothermophilus, and their complexes with RNA or its regulator anti-TRAP protein (AT), by electrospray ionization mass spectrometry (ESI-MS). Wild-type TRAP mainly forms homo-11mer rings. The mutant used carries three copies of the TRAP monomer on a single polypeptide chain so that it associates to form a 12mer ring with four polypeptide molecules. Mass spectra showed that both the wild-type TRAP 1lmer and the mutant TRAP 12mer can bind a cognate single-stranded RNA molecule with a molar ratio of 1:1. The crystal structure of wild-type TRAP complexed with AT shows a TRAP 12mer ring surrounded by six AT trimers. However, nanoESI-MS of wild-type TRAP mixed with AT shows four species with different binding stoichiometries, and the complex observed by crystallography represents only a minor species in solution; most of the TRAP remains in an 11mer ring form. Mass spectra of mutant TRAP showed only a single species, TRAP 12mer + six copies of AT trimer, which is observed by crystallography. These results suggest that crystallization selects only the most symmetrical TRAP-AT complex from the solution, whereas ESI-MS can take a 'snapshot' of all the species in solution.

Influenza A virus is a major human and animal pathogen with the potential to cause catastrophic loss of life. The virus reproduces rapidly, mutates frequently and occasionally crosses species barriers. [...]

In archaea, RNA endonucleases that act specifically on RNA with bulge-helix-bulge motifs play the main role in the recognition and excision of introns, while the eukaryal enzymes use a measuring mechanism to determine the positions of the universally positioned splice sites relative to the conserved domain of pre-tRNA. Two crystallographic structures of tRNA intron-splicing endonuclease from Thermoplasma acidophilum DSM 1728 (End[A.sub.Ta]) have been solved to 2.5-[Angstrom], and 2.7-[Angstrom] resolution by molecular replacement, using the 2.7-[Angstrom] resolution data as the initial model and the single-wavelength anomalous-dispersion phasing method using selenomethionine as anomalous signals, respectively. The models show that End[A.sub.Ta] is a homodimer and that it has overall folding similar to that of other archaeal tRNA endonucleases. From structural and mutational analyses of H236A, Y229F, and K265I in vitro, we have demonstrated that they play critical roles in recognizing the splice site and in cleaving the pre-tRNA substrate.

The numerous crystal studies undertaken to determine the structure of partially liganded Hbs or Hbs restrained by cross-links or the crystal lattice are reported. The experiments were conducted using the cross-linking reagent bis(3,5-dibromosalicyl)-fumarate, which specifically links the two beta subunits via Lys 82.

Author(s): Byung-Je Sung [1, 4]; Kwang Yeon Hwang (corresponding author) [1, 4]; Young Ho Jeon [1, 4]; Jae Il Lee [1, 4]; Yong-Seok Heo [1]; Jin Hwan Kim [1]; Jinho [...]