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Calmodulin regulates ryanodine receptor-mediated Ca 2+ release through a conserved binding site. The crystal structure of Ca 2+ -calmodulin bound to this conserved site reveals that calmodulin recognizes two hydrophobic anchor residues at a novel “1-17” spacing that brings the calmodulin lobes close together but prevents them from contacting one another. NMR residual dipolar couplings...
The core of swapped-hairpin and double-psi β barrels is formed by duplication of a conserved βαβ element, suggesting a common evolutionary origin. The path connecting the two folds is unclear as the two barrels are not interconvertible by a simple topological modification, such as circular permutation. We have identified a protein family whose sequence properties are intermediate to the two folds...
C2a provides the catalytic center to the convertase complexes of the classical and lectin-binding pathways of complement activation. We determined two crystal structures of full-length C2a, with and without a pseudo ligand bound. Both structures reveal a near-active conformation of the catalytic center of the serine protease domains, while the von Willebrand factor A-type domains display an intermediate...
In this issue of Structure, Lankas and coworkers (Lankas et al., 2006) use molecular dynamics simulations of highly strained 94 base-pair DNA circles to show DNA kinking (unstacking of base pairs). The significance of such kinks is surprisingly controversial.
A central event in the invasion of a host cell by an enveloped virus is the fusion of viral and cell membranes. For many viruses, membrane fusion is driven by specific viral surface proteins that undergo large-scale conformational rearrangements, triggered by exposure to low pH in the endosome upon internalization. Here, we present evidence suggesting that in both class I (helical hairpin proteins)...
Recent experiments on minicircle formation suggest that a conformational mechanism other than smooth deformation may be playing a role in enhancing DNA flexibility. Both local base unpairing and kink formation have been suggested as possible explanations. Although kinks within isolated DNA were proposed 30 years ago, they have, until now, only been observed within DNA complexed with proteins. In order...
Structure propensities of amino acids are important determinants in guiding proteins' local and global structure formation. We constructed a phage display library—a hexa-HIS tag upstream of a CXXC (X stands for any of the 20 natural amino acids) motif appending N-terminal to the minor capsid protein pIII of M13KE filamentous phage—and developed a novel directed-evolution procedure to select for amino...
Pheromone-binding proteins (PBP) supply olfactory neuron cells with pheromones by binding the ligands they are tailored for and carrying them to their receptor. The function of a PBP as an efficient carrier requires fast ligand uptake and release. The molecular basis of the ligand-binding mechanism was addressed here for the intriguing case of the PBP of the silk moth Bombyx mori. This PBP completely...
Prolyl-tRNA synthetases (ProRSs) are unique among synthetases in that they have diverse architectures, notably the variable presence of a cis-editing domain homologous to the freestanding deacylase proteins YbaK and ProX. Here, we describe crystal structures of two bacterial ProRSs from the pathogen Enterococcus faecalis, which possesses an editing domain, and from Rhodopseudomonas palustris, which...
Pheromone-binding proteins are postulated to contribute to the exquisite specificity of the insect's olfactory system, acting as a filter by preferentially binding only one of the components of the natural pheromone. Here, we investigated the possible discrimination of the two very similar components of the natural pheromone gland from the silk moth, Bombyx mori, bombykol and bombykal, by the only...
Argonaute proteins are key components of the RNA-induced silencing complex (RISC). They provide both architectural and catalytic functionalities associated with small interfering RNA (siRNA) guide strand recognition and subsequent guide strand-mediated cleavage of complementary mRNAs. We report on the 3.0 Å crystal structures of 22-mer and 26-mer siRNAs bound to Aquifex aeolicus Argonaute (Aa-Ago),...
Defects in the mitochondrial protein frataxin are responsible for Friedreich ataxia, a neurodegenerative and cardiac disease that affects 1:40,000 children. Here, we present the crystal structures of the iron-free and iron-loaded frataxin trimers, and a single-particle electron microscopy reconstruction of a 24 subunit oligomer. The structures reveal fundamental aspects of the frataxin mechanism....
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