scholarly journals Structural insights into the nucleic acid remodeling mechanisms of the yeast THO-Sub2 complex

eLife ◽  
2020 ◽  
Vol 9 ◽  
Author(s):  
Sandra K Schuller ◽  
Jan M Schuller ◽  
J Rajan Prabu ◽  
Marc Baumgärtner ◽  
Fabien Bonneau ◽  
...  
Keyword(s):  
Nucleic Acid ◽  
Conformational Changes ◽  
Molecular Mechanisms ◽  
Cryo Electron Microscopy ◽  
Messenger Ribonucleoprotein ◽  
Rna:Dna Hybrid ◽  
Structural Architecture ◽  
Structural Insights ◽  
Resolution Structure ◽  
Active Genes

The yeast THO complex is recruited to active genes and interacts with the RNA-dependent ATPase Sub2 to facilitate the formation of mature export-competent messenger ribonucleoprotein particles and to prevent the co-transcriptional formation of RNA:DNA-hybrid-containing structures. How THO-containing complexes function at the mechanistic level is unclear. Here, we elucidated a 3.4 Å resolution structure of Saccharomyces cerevisiae THO-Sub2 by cryo-electron microscopy. THO subunits Tho2 and Hpr1 intertwine to form a platform that is bound by Mft1, Thp2, and Tex1. The resulting complex homodimerizes in an asymmetric fashion, with a Sub2 molecule attached to each protomer. The homodimerization interfaces serve as a fulcrum for a seesaw-like movement concomitant with conformational changes of the Sub2 ATPase. The overall structural architecture and topology suggest the molecular mechanisms of nucleic acid remodeling during mRNA biogenesis.

scholarly journals Structural insights into the activation of human calcium-sensing receptor

2021 ◽  
Author(s):  
Xiaochen Chen ◽  
Lu Wang ◽  
Zhanyu Ding ◽  
Qianqian Cui ◽  
Li Han ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Large Scale ◽  
Transmembrane Domains ◽  
Structural Basis ◽  
Calcium Sensing Receptor ◽  
Calcium Sensing ◽  
Cryo Electron Microscopy ◽  
Activation Mechanisms ◽  
G Protein Coupled ◽  
Structural Insights

AbstractHuman calcium-sensing receptor (CaSR) is a G-protein-coupled receptor that maintains Ca2+ homeostasis in serum. Here, we present the cryo-electron microscopy structures of the CaSR in the inactive and active states. Complemented with previously reported crystal structures of CaSR extracellular domains, it suggests that there are three distinct conformations: inactive, intermediate and active state during the activation. We used a negative allosteric nanobody to stabilize the CaSR in the fully inactive state and found a new binding site for Ca2+ ion that acts as a composite agonist with L-amino acid to stabilize the closure of active Venus flytraps. Our data shows that the agonist binding leads to the compaction of the dimer, the proximity of the cysteine-rich domains, the large-scale transitions of 7-transmembrane domains, and the inter-and intrasubunit conformational changes of 7-transmembrane domains to accommodate the downstream transducers. Our results reveal the structural basis for activation mechanisms of the CaSR.

scholarly journals Near-Atomic Resolution Structure of a Highly Neutralizing Fab Bound to Canine Parvovirus

2016 ◽  
Vol 90 (21) ◽  
pp. 9733-9742 ◽  
Author(s):  
Lindsey J. Organtini ◽  
Hyunwook Lee ◽  
Sho Iketani ◽  
Kai Huang ◽  
Robert E. Ashley ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Receptor Binding ◽  
Conformational Changes ◽  
De Novo ◽  
Mutational Analysis ◽  
Antibody Fragment ◽  
Canine Parvovirus ◽  
Single Chain ◽  
Cryo Electron Microscopy ◽  
Resolution Structure

ABSTRACT Canine parvovirus (CPV) is a highly contagious pathogen that causes severe disease in dogs and wildlife. Previously, a panel of neutralizing monoclonal antibodies (MAb) raised against CPV was characterized. An antibody fragment (Fab) of MAb E was found to neutralize the virus at low molar ratios. Using recent advances in cryo-electron microscopy (cryo-EM), we determined the structure of CPV in complex with Fab E to 4.1 Å resolution, which allowed de novo building of the Fab structure. The footprint identified was significantly different from the footprint obtained previously from models fitted into lower-resolution maps. Using single-chain variable fragments, we tested antibody residues that control capsid binding. The near-atomic structure also revealed that Fab binding had caused capsid destabilization in regions containing key residues conferring receptor binding and tropism, which suggests a mechanism for efficient virus neutralization by antibody. Furthermore, a general technical approach to solving the structures of small molecules is demonstrated, as binding the Fab to the capsid allowed us to determine the 50-kDa Fab structure by cryo-EM. IMPORTANCE Using cryo-electron microscopy and new direct electron detector technology, we have solved the 4 Å resolution structure of a Fab molecule bound to a picornavirus capsid. The Fab induced conformational changes in regions of the virus capsid that control receptor binding. The antibody footprint is markedly different from the previous one identified by using a 12 Å structure. This work emphasizes the need for a high-resolution structure to guide mutational analysis and cautions against relying on older low-resolution structures even though they were interpreted with the best methodology available at the time.

scholarly journals Molecular mechanisms of substrate-controlled ring dynamics and sub-stepping in a nucleic-acid dependent hexameric motor

2016 ◽  
Author(s):  
Nathan D. Thomsen ◽  
Michael R. Lawson ◽  
Lea B. Witkowsky ◽  
Song Qu ◽  
James M. Berger
Keyword(s):  
Nucleic Acid ◽  
Conformational Changes ◽  
Molecular Motors ◽  
Structural Changes ◽  
Molecular Mechanisms ◽  
Atp Hydrolysis ◽  
Ring Closure ◽  
Structural Studies ◽  
Saxs Data ◽  
Structural Methods

ABSTRACTRing-shaped hexameric helicases and translocases support essential DNA, RNA, and protein-dependent transactions in all cells and many viruses. How such systems coordinate ATPase activity between multiple subunits to power conformational changes that drive the engagement and movement of client substrates is a fundamental question. Using the E. coli Rho transcription termination factor as a model system, we have employed solution and crystallographic structural methods to delineate the range of conformational changes that accompany distinct substrate and nucleotide cofactor binding events. SAXS data show that Rho preferentially adopts an open-ring state in solution, and that RNA and ATP are both required to cooperatively promote ring closure. Multiple closed-ring structures with different RNA substrates and nucleotide occupancies capture distinct catalytic intermediates accessed during translocation. Our data reveal how RNA-induced ring closure templates a sequential ATP-hydrolysis mechanism, provide a molecular rationale for how the Rho ATPase domains distinguishes between distinct RNA sequences, and establish the first structural snapshots of substepping events in a hexameric helicase/translocase.SIGNIFICANCEHexameric, ring-shaped translocases are molecular motors that convert the chemical energy of ATP hydrolysis into the physical movement of protein and nucleic acid substrates. Structural studies of several distinct hexameric translocases have provided insights into how substrates are loaded and translocated; however, the range of structural changes required for coupling ATP turnover to a full cycle of substrate loading and translocation has not been visualized for any one system. Here, we combine low-and high-resolution structural studies of the Rho helicase, defining for the first time the ensemble of conformational transitions required both for substrate loading in solution and for substrate movement by a processive hexameric translocase.

scholarly journals Mechanistic insight into substrate processing and allosteric inhibition of human p97

2021 ◽  
Author(s):  
Man Pan ◽  
Yuanyuan Yu ◽  
Huasong Ai ◽  
Qingyun Zheng ◽  
Yuan Xie ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Cellular Protein ◽  
Power Stroke ◽  
Cryo Electron Microscopy ◽  
D2 Domain ◽  
The Central Nervous System ◽  
Degenerative Disorder ◽  
Substrate Processing ◽  
Structural Insights ◽  
Insight Into

ABSTRACTp97, also known as valosin-containing protein (VCP), processes ubiquitinated substrates and plays a central role in cellular protein homeostasis. Mutations in human p97 are associated with multisystem proteinopathy (MSP), a dominantly inherited degenerative disorder that can affect muscle, bone and the central nervous system. It is also a drug target for cancer therapy with various inhibitors developed over the past decade. Despite significant structural insights into the fungal homologue of p97, Cdc48, little is known about how human p97 processes its substrates and how the activity is allosterically affected by inhibitors. Here, we report a series of cryo-electron microscopy (cryo-EM) structures of substrate-engaged human p97 complex with resolutions ranging from 2.9 to 3.8 Å that captured “power stroke”-like motions of both the D1 and D2 ATPase rings of p97. The structures elucidated how the unfolded substrate is engaged in the pore at atomic level. Critical conformational changes of the inter-subunit signaling (ISS) motifs were revealed, providing molecular insights into substrate translocation. Furthermore, we also determined cryo-EM structures of human p97 in complex with NMS-873, the most potent p97 inhibitor, at a resolution of 2.4 Å. The structures showed that NMS-873 binds at a cryptic groove in the D2 domain and interacts with the ISS motif, preventing its conformational change, thus blocking substrate translocation allosterically. Finally, using NMS-873 at a substoichiometric concentration, we captured a series of intermediate states, suggesting how the cofactor Npl4 coordinates with the D1 ring of p97 to initiate the translocation.

scholarly journals Structural insights into integrin α5β1 opening by fibronectin ligand

2021 ◽  
Vol 7 (19) ◽  
pp. eabe9716
Author(s):  
Stephanie Schumacher ◽  
Dirk Dedden ◽  
Roberto Vazquez Nunez ◽  
Kyoko Matoba ◽  
Junichi Takagi ◽  
...  
Keyword(s):  
Ligand Binding ◽  
Conformational Changes ◽  
Metal Ion ◽  
Manganese Ions ◽  
Integrin Α5β1 ◽  
Fibronectin Receptor ◽  
Cryo Electron Microscopy ◽  
Cell Tissue ◽  
Structural Insights ◽  
Adhesion Site

Integrin α5β1 is a major fibronectin receptor critical for cell migration. Upon complex formation, fibronectin and α5β1 undergo conformational changes. While this is key for cell-tissue connections, its mechanism is unknown. Here, we report cryo–electron microscopy structures of native human α5β1 with fibronectin to 3.1-angstrom resolution, and in its resting state to 4.6-angstrom resolution. The α5β1-fibronectin complex revealed simultaneous interactions at the arginine-glycine-aspartate loop, the synergy site, and a newly identified binding site proximal to adjacent to metal ion–dependent adhesion site, inducing the translocation of helix α1 to secure integrin opening. Resting α5β1 adopts an incompletely bent conformation, challenging the model of integrin sharp bending inhibiting ligand binding. Our biochemical and structural analyses showed that affinity of α5β1 for fibronectin is increased with manganese ions (Mn2+) while adopting the half-bent conformation, indicating that ligand-binding affinity does not depend on conformation, and α5β1 opening is induced by ligand-binding.

scholarly journals Structural Insights into the BRAF Monomer-to-dimer Transition Mediated by RAS Binding

2021 ◽  
Author(s):  
Juliana Andrea Martinez Fiesco ◽  
David E Durrant ◽  
Deborah K Morrison ◽  
Ping Zhang
Keyword(s):  
Electron Microscopy ◽  
Conformational Changes ◽  
Dynamic Process ◽  
Mammalian Cells ◽  
Dual Function ◽  
Unresolved Issue ◽  
Raf Kinase ◽  
Cryo Electron Microscopy ◽  
Terminal Site ◽  
Structural Insights

An unresolved issue in RAF kinase signaling is how binding of autoinhibited RAF monomers to activated RAS initiates the conformational changes required to form active RAF dimers. Here, we present cryo-electron microscopy structures of full-length BRAF complexes derived from mammalian cells: autoinhibited monomeric BRAF:14-3-32:MEK and BRAF:14-3-32 complexes and an inhibitor-bound, dimeric BRAF2:14-3-32 complex, at 3.7, 4.1, and 3.9 Å resolution, respectively. The RAS binding domain (RBD) of BRAF is resolved in the autoinhibited structures, and we find that neither MEK nor ATP binding is required to stabilize the autoinhibited complexes. Notably, the RBD was found to interact extensively with the 14-3-3 protomer bound to the BRAF C-terminal site. Moreover, through structure-guided mutational studies, our findings indicate that RAS-RAF binding is a dynamic process and that RBD residues at the 14-3-3 interface have a dual function, first stabilizing RBD orientation in the autoinhibited state and then contributing to full RAS contact.

Structural insights into immunoglobulin M

Science ◽  
2020 ◽  
Vol 367 (6481) ◽  
pp. 1014-1017 ◽  
Author(s):  
Yaxin Li ◽  
Guopeng Wang ◽  
Ningning Li ◽  
Yuxin Wang ◽  
Qinyu Zhu ◽  
...  
Keyword(s):  
Mucosal Immunity ◽  
Molecular Mechanisms ◽  
Immunoglobulin M ◽  
Structural Basis ◽  
Polymeric Immunoglobulin Receptor ◽  
Immunoglobulin Receptor ◽  
J Chain ◽  
Cryo Electron Microscopy ◽  
Large Conformational Change ◽  
Structural Insights

Immunoglobulin M (IgM) plays a pivotal role in both humoral and mucosal immunity. Its assembly and transport depend on the joining chain (J-chain) and the polymeric immunoglobulin receptor (pIgR), but the underlying molecular mechanisms of these processes are unclear. We report a cryo–electron microscopy structure of the Fc region of human IgM in complex with the J-chain and pIgR ectodomain. The IgM-Fc pentamer is formed asymmetrically, resembling a hexagon with a missing triangle. The tailpieces of IgM-Fc pack into an amyloid-like structure to stabilize the pentamer. The J-chain caps the tailpiece assembly and bridges the interaction between IgM-Fc and the polymeric immunoglobulin receptor, which undergoes a large conformational change to engage the IgM-J complex. These results provide a structural basis for the function of IgM.

scholarly journals Structural basis for activation and gating of IP3 receptors

2021 ◽  
Author(s):  
Emily A Schmitz ◽  
Hirohide Takahashi ◽  
Erkan Karakas
Keyword(s):  
Conformational Changes ◽  
Molecular Mechanisms ◽  
Receptor Activation ◽  
Structural Basis ◽  
Ip3 Receptors ◽  
Cellular Processes ◽  
Cryo Electron Microscopy ◽  
Channel Opening ◽  
High Concentrations ◽  
Type 3

Calcium (Ca2+) is a universal and versatile cellular messenger used to regulate numerous cellular processes in response to external or internal stimuli. A pivotal component of the Ca2+ signaling toolbox in cells is the inositol 1,4,5-triphosphate (IP3) receptors (IP3Rs), which mediate Ca2+ release from the endoplasmic reticulum (ER), controlling cytoplasmic and organellar Ca2+ concentrations. IP3Rs are activated by IP3 and Ca2+, inhibited by Ca2+ at high concentrations, and potentiated by ATP1-3. However, the underlying molecular mechanisms are unclear due to the lack of structures in the active conformation. Here we report cryo-electron microscopy (cryo-EM) structures of human type-3 IP3R in multiple gating conformations; IP3-ATP bound pre-active states with closed channels, IP3-ATP-Ca2+ bound active state with an open channel, and IP3-ATP-Ca2+ bound inactive state with a closed channel. The structures demonstrate how IP3-induced conformational changes prime the receptor for activation by Ca2+, how Ca2+ binding leads to channel opening, and how ATP modulates the activity, providing insights into the long-sought questions regarding the molecular mechanism of the receptor activation and gating.

High resolution mapping of nucleic acid containing complexes in vitro and in situ

1996 ◽  
Vol 54 ◽  
pp. 48-49
Author(s):  
D. P. Bazett-Jones ◽  
M. J. Hendzel
Keyword(s):  
Nucleic Acid ◽  
High Resolution ◽  
Transcription Initiation ◽  
Molecular Mechanisms ◽  
Heavy Atom ◽  
Regulation Of Transcription ◽  
High Exposure ◽  
Resolution Mapping ◽  
Tata Sequence

Structural analysis of combinations of nucleosomes and transcription factors on promoter and enhancer elements is necessary in order to understand the molecular mechanisms responsible for the regulation of transcription initiation. Such complexes are often not amenable to study by high resolution crystallographic techniques. We have been applying electron spectroscopic imaging (ESI) to specific problems in molecular biology related to transcription regulation. There are several advantages that this technique offers in studies of nucleoprotein complexes. First, an intermediate level of spatial resolution can be achieved because heavy atom contrast agents are not necessary. Second, mass and stoichiometric relationships of protein and nucleic acid can be estimated by phosphorus detection, an element in much higher proportions in nucleic acid than protein. Third, wrapping or bending of the DNA by the protein constituents can be observed by phosphorus mapping of the complexes. Even when ESI is used with high exposure of electrons to the specimen, important macromolecular information may be provided. For example, an image of the TATA binding protein (TBP) bound to DNA is shown in the Figure (top panel). It can be seen that the protein distorts the DNA away from itself and much of its mass sits off the DNA helix axis. Moreover, phosphorus and mass estimates demonstrate whether one or two TBP molecules interact with this particular promoter TATA sequence.

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