scholarly journals Membrane Insertion and Membrane-Induced Conformational Changes of Talin F2F3 Triggering Integrin Activation

2011 ◽  
Vol 100 (3) ◽  
pp. 254a-255a
Author(s):  
Mark J. Arcario ◽  
Emad Tajkhorshid
Keyword(s):  
Conformational Changes ◽  
Membrane Insertion ◽  
Integrin Activation

New insights into the structural basis of integrin activation

Blood ◽  
2003 ◽  
Vol 102 (4) ◽  
pp. 1155-1159 ◽  
Author(s):  
Jian-Ping Xiong ◽  
Thilo Stehle ◽  
Simon L. Goodman ◽  
M. Amin Arnaout
Keyword(s):  
Conformational Changes ◽  
Structural Changes ◽  
Structural Basis ◽  
Integrin Activation ◽  
Cellular Functions ◽  
Electron Microscopic ◽  
The Past ◽  
Intracellular Signals ◽  
Bidirectional Signaling ◽  
New Hypothesis

Abstract Integrins are cell adhesion receptors that communicate biochemical and mechanical signals in a bidirectional manner across the plasma membrane and thus influence most cellular functions. Intracellular signals switch integrins into a ligand-competent state as a result of elicited conformational changes in the integrin ectodomain. Binding of extracellular ligands induces, in turn, structural changes that convey distinct signals to the cell interior. The structural basis of this bidirectional signaling has been the focus of intensive study for the past 3 decades. In this perspective, we develop a new hypothesis for integrin activation based on recent crystallographic, electron microscopic, and biochemical studies.

scholarly journals How Melittin Inserts into Cell Membrane: Conformational Changes, Inter-Peptide Cooperation, and Disturbance on the Membrane

Molecules ◽  
2019 ◽  
Vol 24 (9) ◽  
pp. 1775 ◽  
Author(s):  
Jiajia Hong ◽  
Xuemei Lu ◽  
Zhixiong Deng ◽  
Shufeng Xiao ◽  
Bing Yuan ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Membrane Structure ◽  
Lipid Extraction ◽  
Immune Defense ◽  
Resistant Bacteria ◽  
Membrane Insertion ◽  
Free Energy Barrier ◽  
Surface Binding ◽  
Bacterial Killing ◽  
Bacterial Membranes

Antimicrobial peptides (AMPs), as a key component of the immune defense systems of organisms, are a promising solution to the serious threat of drug-resistant bacteria to public health. As one of the most representative and extensively studied AMPs, melittin has exceptional broad-spectrum activities against microorganisms, including both Gram-positive and Gram-negative bacteria. Unfortunately, the action mechanism of melittin with bacterial membranes, especially the underlying physics of peptide-induced membrane poration behaviors, is still poorly understood, which hampers efforts to develop melittin-based drugs or agents for clinical applications. In this mini-review, we focus on recent advances with respect to the membrane insertion behavior of melittin mostly from a computational aspect. Membrane insertion is a prerequisite and key step for forming transmembrane pores and bacterial killing by melittin, whose occurrence is based on overcoming a high free-energy barrier during the transition of melittin molecules from a membrane surface-binding state to a transmembrane-inserting state. Here, intriguing simulation results on such transition are highlighted from both kinetic and thermodynamic aspects. The conformational changes and inter-peptide cooperation of melittin molecules, as well as melittin-induced disturbances to membrane structure, such as deformation and lipid extraction, are regarded as key factors influencing the insertion of peptides into membranes. The associated intermediate states in peptide conformations, lipid arrangements, membrane structure, and mechanical properties during this process are specifically discussed. Finally, potential strategies for enhancing the poration ability and improving the antimicrobial performance of AMPs are included as well.

A Glycan Wedge Between βTD and βI Domains Activates Integrin αIIbβ3,

Blood ◽  
2011 ◽  
Vol 118 (21) ◽  
pp. 3259-3259
Author(s):  
Jun Yamanouchi ◽  
Takaaki Hato ◽  
Hiroshi Fujiwara ◽  
Yoshihiro Yakushijin ◽  
Masaki Yasukawa
Keyword(s):  
Ligand Binding ◽  
Conformational Changes ◽  
Conflicts Of Interest ◽  
Consensus Sequence ◽  
Glycosylation Site ◽  
Tail Domain ◽  
Wild Type ◽  
Integrin Activation ◽  
Integrin Αiibβ3 ◽  
Constitutively Active

Abstract Abstract 3259 Integrin αIIbβ3 undergoes allosteric conformational changes in its extracellular domains, resulting in integrin activation that allows high affinity binding with soluble ligands. The crystal structure of the integrin β subunit revealed an interaction of the β-tail domain (βTD) with the βI domain containing ligand-binding sites, suggesting that βTD may be involved in allosteric mechanism for integrin activation. However, previous studies have shown conflicting results on the functional role of βTD in integrin activation. In this study, we conducted site-directed mutagenesis in the βTD domain and tested ligand binding to αIIbβ3 mutants. We produced αIIbβ3 mutants in which the β3TD loop residues (DSSG) were substituted with the corresponding β1 (NGNN) or β2TD residues (DGMD). The αIIbβ3 mutants were expressed on the surface of CHO cells by cotransfection of mutant β3 and wild-type αIIb cDNAs, and were tested for binding of PAC1, a ligand-mimetic anti-αIIbβ3 antibody. The NGNN, but not DGMD mutant bound significant PAC1 binding without any stimulation, indicating a constitutively active state. To identify the residue(s) responsible for αIIbβ3 activation in the βTD, we produced αIIbβ3 mutants in which the individual residues in the β3TD loop were substituted with the corresponding β1TD residues. Among them, only G675N bound significant PAC1 binding without any stimulation. Since G675N mutation creates a sequence known to be a consensus sequence for glycosylation (Asn-X-Ser/Thr), it is possible that the insertion of glycans into the βTD loop induces conformational changes in αIIbβ3 which allow ligand binding. To test this hypothesis, we added substitution of S677 with Thr, Ala or Asp to the G675N mutation. The resultant G675N/S677T double mutant, in which the N-glycosylation site was preserved, was constitutively active. In contrast, G675N/S677A and G675N/S677D, in which the N-glycosylation site was disrupted, were in an inactive state. These results suggest that an artificial glycan wedge between βTD and βI domains activates αIIbβ3. However, our study does not provide evidence that the βTD domain constrains wild type αIIbβ3 inactive although the separation of βTD and βI domains may be able to activate integrins. Disclosures: No relevant conflicts of interest to declare.

scholarly journals Membrane insertion of α-xenorhabdolysin in near-atomic detail

2018 ◽  
Author(s):  
Evelyn Schubert ◽  
Ingrid R. Vetter ◽  
Daniel Prumbaum ◽  
Pawel A. Penczek ◽  
Stefan Raunser
Keyword(s):  
Conformational Changes ◽  
Mechanism Of Action ◽  
Pathogenic Bacteria ◽  
Structural Model ◽  
Structural Information ◽  
Host Cells ◽  
Membrane Insertion ◽  
Xenorhabdus Nematophila ◽  
Host Cell Membrane ◽  
Pore Complexes

ABSTRACTα-Xenorhabdolysins (Xax) are α-pore-forming toxins (α-PFT) from pathogenic bacteria that form 1-1.3 MDa large pore complexes to perforate the host cell membrane. PFTs are used by a variety of bacterial pathogens as an offensive or defensive mechanism to attack host cells. Due to the lack of structural information, the molecular mechanism of action of Xax toxins is poorly understood. Here, we report the cryo-EM structure of the XaxAB pore complex from Xenorhabdus nematophila at an average resolution of 4.0 Å and the crystal structures of the soluble monomers of XaxA and XaxB at 2.5 Å and 3.4 Å, respectively. The structures reveal that XaxA and XaxB are built similarly and appear as heterodimers in the 12-15 subunits containing pore. The structure of the XaxAB pore represents therefore the first structure of a bi-component α-PFT. Major conformational changes in XaxB, including the swinging out of an amphipathic helix are responsible for membrane insertion. XaxA acts as an activator and stabilizer for XaxB that forms the actual transmembrane pore. Based on our results, we propose a novel structural model for the mechanism of action of Xax toxins.

scholarly journals Crystal structure of the complete integrin αVβ3 ectodomain plus an α/β transmembrane fragment

2009 ◽  
Vol 186 (4) ◽  
pp. 589-600 ◽  
Author(s):  
Jian-Ping Xiong ◽  
Bhuvaneshwari Mahalingham ◽  
Jose Luis Alonso ◽  
Laura Ann Borrelli ◽  
Xianliang Rui ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Conformational Changes ◽  
Integrin Αvβ3 ◽  
Site Directed Mutagenesis ◽  
Live Cells ◽  
Integrin Activation ◽  
Intact Cells ◽  
Fluorescent Lifetime Imaging Microscopy ◽  
Direct Demonstration ◽  
Transmembrane Fragment

We determined the crystal structure of 1TM-αVβ3, which represents the complete unconstrained ectodomain plus short C-terminal transmembrane stretches of the αV and β3 subunits. 1TM-αVβ3 is more compact and less active in solution when compared with ΔTM-αVβ3, which lacks the short C-terminal stretches. The structure reveals a bent conformation and defines the α–β interface between IE2 (EGF-like 2) and the thigh domains. Modifying this interface by site-directed mutagenesis leads to robust integrin activation. Fluorescent lifetime imaging microscopy of inactive full-length αVβ3 on live cells yields a donor–membrane acceptor distance, which is consistent with the bent conformation and does not change in the activated integrin. These data are the first direct demonstration of conformational coupling of the integrin leg and head domains, identify the IE2–thigh interface as a critical steric barrier in integrin activation, and suggest that inside-out activation in intact cells may involve conformational changes other than the postulated switch to a genu-linear state.

scholarly journals Species-specific gamete recognition initiates fusion-driving trimer formation by conserved fusogen HAP2

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jun Zhang ◽  
Jennifer F. Pinello ◽  
Ignacio Fernández ◽  
Eduard Baquero ◽  
Juliette Fedry ◽  
...  
Keyword(s):  
Conformational Changes ◽  
Membrane Insertion ◽  
Structural Studies ◽  
Enveloped Viruses ◽  
Gamete Recognition ◽  
Membrane Attachment ◽  
Trimer Formation ◽  
Species Specific ◽  
Specific Membrane ◽  
Fusion Loop

AbstractRecognition and fusion between gametes during fertilization is an ancient process. Protein HAP2, recognized as the primordial eukaryotic gamete fusogen, is a structural homolog of viral class II fusion proteins. The mechanisms that regulate HAP2 function, and whether virus-fusion-like conformational changes are involved, however, have not been investigated. We report here that fusion between plus and minus gametes of the green alga Chlamydomonas indeed requires an obligate conformational rearrangement of HAP2 on minus gametes from a labile, prefusion form into the stable homotrimers observed in structural studies. Activation of HAP2 to undergo its fusogenic conformational change occurs only upon species-specific adhesion between the two gamete membranes. Following a molecular mechanism akin to fusion of enveloped viruses, the membrane insertion capacity of the fusion loop is required to couple formation of trimers to gamete fusion. Thus, species-specific membrane attachment is the gateway to fusion-driving HAP2 rearrangement into stable trimers.

Talin controls integrin activation

2004 ◽  
Vol 32 (3) ◽  
pp. 434-437 ◽  
Author(s):  
D.A. Calderwood
Keyword(s):  
Conformational Changes ◽  
Critical Role ◽  
Dynamic Control ◽  
Common Element ◽  
Actin Binding ◽  
Cytoplasmic Domains ◽  
Integrin Activation ◽  
Intracellular Signals ◽  
Integrin Binding Site ◽  
Activation Pathways

Tight, dynamic control of the affinity of integrin adhesion receptors for their extracellular ligands (integrin activation) is essential for the development and functioning of multicellular organisms. Integrin activation is controlled by intracellular signals that, through their action on integrin cytoplasmic domains, induce conformational changes in integrin extracellular domains, resulting in increased affinity for the ligand. Recent results indicate that the binding of talin, a major actin-binding protein, to integrin β tails represents a final common step in integrin activation pathways. The major integrin-binding site lies within the talin FERM (four-point-one, ezrin, radixin, moesin) domain, and binding occurs via a variant of the classical PTB domain (phosphotyrosine-binding domain)–NPxY interaction. Formation of this talin–integrin complex plays a critical role in integrin activation, since mutations, in either talin or integrin β tails, which disrupt complex formation, inhibit integrin activation. Furthermore, use of RNA interference to knockdown talin expression selectively reveals that talin is essential for integrin activation in response to physiological agonists. Thus the association of the cytoskeletal protein talin with integrin β cytoplasmic domains is a critical step during integrin activation, and regulation of this step may be a final common element in the signalling pathways that control integrin activation.

scholarly journals Membrane insertion of α-xenorhabdolysin in near-atomic detail

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Evelyn Schubert ◽  
Ingrid R Vetter ◽  
Daniel Prumbaum ◽  
Pawel A Penczek ◽  
Stefan Raunser
Keyword(s):  
Conformational Changes ◽  
Structural Model ◽  
Structural Information ◽  
Host Cells ◽  
Membrane Insertion ◽  
Amphipathic Helix ◽  
Xenorhabdus Nematophila ◽  
Host Cell Membrane ◽  
Molecular Mechanism Of Action ◽  
Pore Complexes

α-Xenorhabdolysins (Xax) are α-pore-forming toxins (α-PFT) that form 1–1.3 MDa large pore complexes to perforate the host cell membrane. PFTs are used by a variety of bacterial pathogens to attack host cells. Due to the lack of structural information, the molecular mechanism of action of Xax toxins is poorly understood. Here, we report the cryo-EM structure of the XaxAB pore complex from Xenorhabdus nematophila and the crystal structures of the soluble monomers of XaxA and XaxB. The structures reveal that XaxA and XaxB are built similarly and appear as heterodimers in the 12–15 subunits containing pore, classifying XaxAB as bi-component α-PFT. Major conformational changes in XaxB, including the swinging out of an amphipathic helix are responsible for membrane insertion. XaxA acts as an activator and stabilizer for XaxB that forms the actual transmembrane pore. Based on our results, we propose a novel structural model for the mechanism of Xax intoxication.

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