Positive Cooperativity Research Articles

Anionic behavior and single-molecule crystal in fullerene confinements: A contribution from DFT energy decomposition and cooperativity analyses.

The recently proposed systems of various anions (A) confined inside C60 , A- @ C60 , which in turn behave as large and stable anions, (A @ C60 )- , can find potential applications in various fields. On the other hand, it has earlier been shown that from the dihalogens (X2 ) encapsulated C60 , X2 @ C60 , only F2 @ C60 can be introduced as a system in which the cage acts as a cation C60 + and interacts with an endohedral anion, F2 - , forming the F2 - @ C60 + as a single-molecule crystal compound. In this work, two density functional theory energy decomposition analysis (EDA) schemes, where in one of them the noninteracting kinetic, electrostatic, and exchange-correlation energies come into play while another scheme, called as EDA-SBL, includes the steric, electrostatic, and quantum effects as essential ingredients (S. Liu, J. Chem. Phys. 2007, 126, 244103), are utilized to find out what energetic components govern the unique characteristics of the (A @ C60 )- and X2 @ C60 confinements. It is shown that the noninteracting kinetic energy and steric energies have important contributions to the total interaction energies for the considered systems. However, there are other confinements for which the electrostatic and exchange-correlation contributions play also imperative roles. Furthermore, we find reasonable correlations between interaction energies and their components as well as the energetic components themselves, leading to an alternative EDA scheme including the noninteracting kinetic, steric, and electrostatic energies for investigations on other endohedral fullerenes. Extending our analyses to large size confinements, Cl- @ Cn with n up to 90 as illustrative examples, the quantitative cooperativity concept is also explored, where the positive and negative cooperativity profiles unveil a specific size of the anionic confinements to form the most stable large anion.

From Sevastopol to Sukhumi – and back again: British naval liaison in action with the Red Navy in the Black Sea, 1941-1945

During World War II, Britain established a liaison officer with the Soviet Fleet in the Black Sea. Military cooperation between the western allies and the USSR is often regarded as minimal and unsuccessful, but this post demonstrated more positive cooperation. There were two crises when there were accusations of misbehaviour, and there were occasions when he was idle, but these were handled successfully in Whitehall. The post endured, and successive officers did a good job of operational liaison, as well as providing unique intelligence insights from a Soviet fighting front, right up until the end of the war in Europe.

Cooperativity Between Orthosteric Inhibitors and Allosteric Inhibitor 8-Anilino-1-Naphthalene Sulfonic Acid (ANS) in Cyclin-Dependent Kinase 2

While kinases have been attractive targets to combat many diseases, including cancer, selective kinase inhibition has been challenging, because of the high degree of structural homology in the active site, where many kinase inhibitors bind. We have previously discovered that 8-anilino-1-naphthalene sulfonic acid (ANS) binds an allosteric pocket in cyclin-dependent kinase 2 (Cdk2). Here, we detail the positive cooperativity between ANS and orthosteric Cdk2 inhibitors dinaciclib and roscovitine, which increase the affinity of ANS toward Cdk2 5-fold to 10-fold, and the relatively noncooperative effects of ATP. We observe these effects using a fluorescent binding assay and heteronuclear single quantum correlation nuclear magnetic resonance (HSQC NMR), where we noticed a shift from fast exchange to slow exchange upon ANS titration in the presence of roscovitine but not with an ATP mimic. The discovery of cooperative relationships between orthosteric and allosteric kinase inhibitors could further the development of selective kinase inhibitors in general.

Graphene oxide nanofilm and the addition of l-glutamine can promote development of embryonic muscle cells

BackgroundFormation of muscular pseudo-tissue depends on muscle precursor cells, the extracellular matrix (ECM)-mimicking structure and factors stimulating cell differentiation. These three things cooperate and can create a tissue-like structure, however, their interrelationships are relatively unknown. The objective was to study the interaction between surface properties, culture medium composition and heterogeneous cell culture. We would like to demonstrate that changing the surface properties by coating with graphene oxide nanofilm (nGO) can affect cell behaviour and especially their need for the key amino acid l-glutamine (L-Glu).ResultsChicken embryo muscle cells and their precursors, cultured in vitro, were used as the experimental model. The mesenchymal stem cell, collected from the hind limb of the chicken embryo at day 8 were divided into 4 groups; the control group and groups treated with nGO, L-Glu and nGO supplied with L-Glu (nGOxL-Glu). The roughness of the surface of the plastic plate covered with nGO was much lower than a standard plate. The test of nGO biocompatibility demonstrated that the cells were willing to settle on the nGO without any toxic effects. Moreover, nGO by increasing hydrophilicity and reducing roughness and presumably through chemical bonds available on the GO surface stimulated the colonisation of primary stromal cells that promote embryonic satellite cells. The viability significantly increased in cells cultured on nGOxL-Glu. Observations of cell morphology showed that the most mature state of myogenesis was characteristic for the group nGOxL-Glu. This result was confirmed by increasing the expression of MYF5 genes at mRNA and protein levels. nGO also increased the expression of MYF5 and also very strongly the expression of PAX7 at mRNA and protein levels. However, when analysing the expression of PAX7, a positive link was observed between the nGO surface and the addition of L-Glu.ConclusionsThe use of nGO and L-Glu supplement may improve myogenesis and also the myogenic potential of myocytes and their precursors by promoting the formation of satellite cells. Studies have, for the first time, demonstrated positive cooperation between surface properties nGO and L-Glu supplementation to the culture medium regarding the myogenic potential of cells involved in muscle formation.

Indirect reciprocity with simple records

Indirect reciprocity is a foundational mechanism of human cooperation. Existing models of indirect reciprocity fail to robustly support social cooperation: Image-scoring models fail to provide robust incentives, while social-standing models are not informationally robust. Here we provide a model of indirect reciprocity based on simple, decentralized records: Each individual's record depends on the individual's own past behavior alone, and not on the individual's partners' past behavior or their partners' partners' past behavior. When social dilemmas exhibit a coordination motive (or strategic complementarity), tolerant trigger strategies based on simple records can robustly support positive social cooperation and exhibit strong stability properties. In the opposite case of strategic substitutability, positive social cooperation cannot be robustly supported. Thus, the strength of short-run coordination motives in social dilemmas determines the prospects for robust long-run cooperation.

Computational Insights into Molecular Activation and Positive Cooperative Mechanisms of FFAR1 Modulators.

Free fatty acid receptor 1 (FFAR1), a member of class A in G-protein-coupled receptors (GPCRs), is a promising antidiabetic target. The crystal structure of FFAR1 revealed that one agonist (MK-8666) binds to the extracellular vestibule of this receptor, while another (AP8) occupies the surface pocket between transmembrane (TM) helices TM4 and TM5. In this study, we performed 1 μs unbiased molecular dynamics (MD) simulation on each of five systems, to uncover why two ligands in completely different sites both serve as agonists and how they exert a positive synergistic effect together. They are two agonist-bound systems (FFAR1_MK-8666 and FFAR1_AP8), a ternary complex system FFAR1_MK-8666_AP8, an antagonist-bound system (FFAR1_15i), and an unliganded (apo) system, among which the antagonist 15i-bound and apo systems were used as controls. The results showed that Y913.37 played a pivotal role in the activation process of FFAR1. The agonist could disrupt the Y913.37-centered residue interaction network within protein, whereas the antagonist could stabilize the network. Furthermore, our simulations revealed that the hydrophobic layer amino acid residues next to the transmission switch (CWXP) formed a gate and could open only upon agonist activation, which might exert an important role in the formation of water pathway. These results would be helpful for elucidating the molecular activation mechanism of FFAR1 and provide insights into the design and discovery of novel allosteric agonists of FFAR1 for the treatment of type 2 diabetes mellitus (T2DM).

Bimetallic Bis-anion Cascade Complexes of Magnesium in Nonaqueous Solution.

Bimetallic magnesium(II) complexes are gaining significant interest in catalysis, yet their fundamental formation and behavior in organic media remain surprisingly unexplored relative to other divalent cations. To understand key principles of their formation, we investigate symmetric ditopic ligands bearing a phenolic backbone and characterize their ability to form dinuclear magnesium(II) cascade complexes with two bridging anions. High-fidelity production of bimetallic magnesium complexes relative to the monometallic complexes is indicative of positive cooperativity. Binding and recognition of analytes or substrates is a key characteristic of metal cascade complexes and relies on anion exchange, but this is also rarely studied with bimetallic magnesium complexes. Investigations with acetate, phosphate, and pyrophosphate reveal exchange of bridging nitrates using the bis-dipicolylamine complex. Rare seven-coordinate magnesium centers are found for the ester complex. The findings in this study provide formative steps to establish design principles for future generations of bimetallic magnesium(II) complexes.

G3BP1 Is a Tunable Switch that Triggers Phase Separation to Assemble Stress Granules

The mechanisms underlying ribonucleoprotein (RNP) granule assembly, including the basis for establishing and maintaining RNP granules with distinct composition, are unknown. One prominent type of RNP granule is the stress granule (SG), a dynamic and reversible cytoplasmic assembly formed in eukaryotic cells in response to stress. Here, we show that SGs assemble through liquid-liquid phase separation (LLPS) arising from interactions distributed unevenly across a core protein-RNA interaction network. The central node of this network is G3BP1, which functions as a molecular switch that triggers RNA-dependent LLPS in response to a rise in intracellular free RNA concentrations. Moreover, we show that interplay between three distinct intrinsically disordered regions (IDRs) in G3BP1 regulates its intrinsic propensity for LLPS, and this is fine-tuned by phosphorylation within the IDRs. Further regulation of SG assembly arises through positive or negative cooperativity by extrinsic G3BP1-binding factors that strengthen or weaken, respectively, the core SG network.

FUNGSI PONDOK PERSULUKAN BABUSSALAM DALAM PEMBINAAN MORAL DI BATANG KUIS KAMPUNG RUMBIA

<p><em>The function of the Pondok Pesulukan in Moral Development, aims so positively towards the community, ranging from parents, adolescents, and children with the Moral planting that is so impacting for adolescents around the Babussalam Persulukan Pondok in Batang Kuis Rumbia Village. In this study, researchers used a type of field research research with data collection techniques from Mr. Guru Sheikh Abdurrahman Harahap, murshid, as well as Community Leaders, and Village Heads in Batang Kuis Kampung Rumbia in this study with later supported literary studies related to theoretical opinions. Findings of Moral formation research results from Jama'ah: The Jama'ahs in the Babussalam Persulukan are very close to Allah by multiplying or deepening the knowledge that has been applied by Mr. Sheikh Abdurrahman Harahap conducted by researchers the condition of moral coaching activities is going pretty well, done with several methods including the habituation method, the admonition method, the exemplary method, the disciplinary method and the at-targhīb and at-tarhīb methods (rewards and punishments). This can be seen from the positive cooperation between the Teachers and Murshid and the community around the Persulukan environment. This research concludes that the pondok siluk in the thatch village can provide moral guidance through Sufism seems to be more effective than merely doctrine of moral science that is theoretical, so Sufism is expected to overcome the spiritual crisis and moral crisis both so that they become accustomed to doing in life day-to-day, both in the community, family, and at school, there is a need for habituation and exercises that are started from childhood by parents.</em></p><p><strong>Keywords</strong><strong>: </strong><em>Cottage Towards, Moral Guidance.</em><em></em></p>

Bringing a Molecular Plus One: Synergistic Binding Creates Guest-Mediated Three-Component Complexes.

Cethyl-2-methylresorcinarene (A), pyridine (B), and a set of 10 carboxylic acids (Cn) associate to form A·B·Cn ternary assemblies with 1:1:1 stoichiometry, representing a useful class of ternary systems where the guest mediates complex formation between the host and a third component. Although individually weak in solution, the combined strength of the multiple noncovalent interactions organizes the complexes even in a highly hydrogen-bond competing methanol solution, as explored by both experimental and computational methods. The interactions between A·B and Cn are dependent on the pKa values of carboxylic acids. The weak interactions between A and C further reinforce the interactions between A and B, demonstrating positive cooperativity. Our results reveal that the two-component system such as that formed by A and B can form the basis for the development of specific sensors for the molecular recognition of carboxylic acids.

Molecular Electrostatic Potential Reorganization Theory to Describe Positive Cooperativity in Noncovalent Trimer Complexes.

Supramolecular self-assembly and molecular recognition processes are driven mainly by positive cooperativity in noncovalent interactions. Here, we report a large variety of hydrogen-, tetrel-, chalcogen-, pnicogen-, halogen-, aerogen-, and dihydrogen-bonded dimer and trimer complexes, computed using the MP2/6-311++G(d,p) level ab initio theory. The dimer to trimer change is associated with a positive cooperativity in all the complexes. Significant electron density reorganization occurs in monomers because of noncovalent bond formation which is quantified using the change in the molecular electrostatic potential (MESP) at bonded atoms. For a noncovalent dimer XDYA, an electron density flow is observed from the donor molecule XD to acceptor molecule YA. As a result, YA in dimer showed a tendency to form a stronger noncovalent bond with an electron-deficient center of a third molecule, whereas XD in the dimer showed a tendency to form a stronger noncovalent bond with an electron-rich center of a third molecule. The change in change-of-MESP at the donor and acceptor atoms involved in bond formation (ΔΔVn) is used as a parameter to assess the extent of electron donor-acceptor (eDA) interaction in dimers and trimers and found that ΔΔVn is directly proportional to the total binding energy. A cooperativity rule has emerged from this study which states that the electron reorganization in the dimer due to the eDA interaction always enhances its donor-acceptor interactive behavior with a third molecule toward the formation of a noncovalent trimer complex.

Optimizing Bus Line Based on Metro-Bus Integration

Metros are usually built and added on the basis of a completed bus network in Chinese cities. After the metro construction, it is faced with the problem of how to adjust and optimize the original bus lines based on the new metro system. This research mainly proposes a bus line optimization method based on bus and metro integration. In the consideration of the geographical space, the cooperation and competition relationship between bus and metro lines is qualitatively introduced according to the geographical location and service range of metro (800 m radius) and bus (500 m radius) stations. The competition and cooperation indexes are applied to define the co-opetition relationship between bus and metro lines. The bus line optimization model is constructed based on the co-opetition coefficient and Changsha Metro Line Number 2 is chosen as a case study to verify the optimization model. The results show that the positive competition, efficient cooperation, and travel efficiency between metro and bus has been significantly enhanced after optimization. Moreover, this paper provides a reasonable reference for public transport network planning and resource allocation.

Cooperative Substrate Binding Converges to the Closed Conformations in the Sodium-Coupled Melibiose Symporter MelB

MelB belongs to the major facilitator superfamily, and the transport involves an alternating access mechanism. The energetics underscoring the conformational changes is not well understood. By determining substrate binding energy with purified MelB of Salmonella typhimurium (MelBSt) with isothermal titration colorimetry for constructing a thermodynamic cycle, we have shown positive cooperativity between the binding of the co-transported Na+ and melibiose. To correlate the substrate binding and conformational states, in this study, we determined the heat capacity change (ΔCp) for each four steps in this thermodynamic cycle. The thermodynamic parameter ΔCp for ligand binding may mainly reflect the solvation properties of the overall reaction, including the local binding event and associated global protein structural rearrangements. Our data show that the binding of a single ligand to MelBSt, either Na+ or melibiose, exhibits a positive sign of ΔCp, suggesting hydration of MelBSt protein from cavity opening; on the other hand, the binding of both ligands, regardless which one first, exhibits a negative sign of ΔCp, suggesting MelBSt dehydration from cavity closing. MelBSt Trp→dansyl-galactoside FRET was measured by stopped-flow fluorescence, showing a fast binding rate in the presence of Na+. All results are consistent with this interpretation: binding of either single substrate maintains this symporter in open states, where the affinities are lower; and binding of both two substrates to MelBSt shifts the conformational equilibria towards the occluded state to achieve the highest affinities derived from their cooperativity. In other words, the cooperative substrate binding to low-energy state (high-affinity state) spontaneously pushes MelB towards high-energy closed intermediates. This convergency is the core mechanism for symport, using cooperative binding to overcome the energy barrier for conformational changes and also to forbid the transport of either single substrate alone.

Cover Feature: Entropy‐Driven Cooperativity in the Guest Binding of an Octaphosphonate Bis‐cavitand (Chem. Eur. J. 14/2020)

An octaphosphonate biscavitand showed an uncommon entropy-driven positive cooperativity in the guest binding. The water molecules formed the cluster-like assemblies at the two cavities of the biscavitand in chloroform. The guest binding broke the hydrogen-bonded water molecules, which is responsible for the entropy-driven cooperativity in the multiple guest binding. More information can be found in the Full Paper by D. Shimoyama and T. Haino on page 3074.

Revealing the Positive Binding Cooperativity Mechanism between the Orthosteric and the Allosteric Antagonists of CCR2 by Metadynamics and Gaussian Accelerated Molecular Dynamics Simulations.

CC chemokine receptor 2 (CCR2) and its endogenous CC chemokine ligands are associated with numerous inflammatory, neurodegenerative diseases, and cancer. CCR2 is becoming an attractive target in the treatment of autoimmune disease and neurodegenerative diseases. The orthosteric antagonist BMS-681 and allosteric antagonist CCR2-RA-[R] of CCR2 show positive binding cooperativity. We performed well-tempered metadynamics simulations and Gaussian accelerated MD simulations to reveal the influence of the orthosteric antagonist on the unbinding of allosteric antagonist of CCR2. We revealed different unbinding pathways of CCR2-RA-[R] in binary complex CCR2-VT5 and ternary complex CCR2-73R-VT5. The different unbinding pathways of CCR2-RA-[R] are due to the conformational dynamics of TM6. We obtained the significant conformational differences of the intracellular side of TM6 upon CCR2 binding to different ligands by GaMD simulation. The conformational dynamics of TM6 are consistent with the unbinding pathway analysis. GaMD simulations indicate that BMS-681 binding restricts the bend of intracellular side of TM6 by stabilizing the extracellular sides of TM6 and TM7. The charged residues Arg2065.43 of TM5 and Glu2917.39 of TM7 play key roles in stabling TM7 and TM6. TM6 and TM7 are crucial components in the orthosteric and allosteric binding sites. Our results illustrate the conformational details about the effect of the orthosteric antagonist on the allosteric antagonist of CCR2. The conformational dynamics of CCR2 upon binding to different ligands can provide a rational basis for development of allosteric ligands of CCR2.

Positive and negative cooperativity of TNF and Interferon-\u03b3 in regulating synovial fibroblast function and B cell survival in fibroblast/B cell co-cultures

Synovial fibroblasts (SF) were reported to produce B cell activating factor (BAFF) in response to stimulation with interferon-γ (IFN-γ) or tumor necrosis factor (TNF). However, the influence of these pro-inflammatory cytokines on other receptors/ligands of the TNF superfamily or associated cytokine receptors in SF has not been investigated yet. Here we show the differential regulation of BAFF (CD257), Fn14 (CD266), TACI (CD267), BAFF-R (CD268), BCMA (CD269), CD40 ligand (CD40L, CD154), IFN-γR (CD119), Leptin receptor (ObR, CD295), VCAM-1 (CD106) and membrane TGF-β in isolated SF and the impact of IFN-γ/TNF co-incubation on proliferation, IL-6 and IL-8 production. In addition, the impact of differentially stimulated SF on B cell survival in co-cultures was assessed. Surface cytokines and cytokine receptors were detected by flow cytometry. Soluble cytokine receptors and cytokines were quantified by ELISA. Proliferation was assessed by cell titer blue. Murine B cell survival in fibroblast/ B cell co-cultures was determined by annexin V/propidium iodide staining and flow cytometry. IFN-γ together with TNF synergistically and significantly increased the cell surface levels of BAFF, Fn14, TACI, BAFF-R, BCMA, CD40L, ObR and IFN-γR in rheumatoid arthritis SF after 72 h incubation. Soluble BAFF was only induced by IFN-γ and inhibited by TNF. Addition of TWEAK had no influence on proliferation or IL-8 production but decreased TNF-induced IL-6 production, whereas APRIL, BAFF and leptin did not modulate TNF or TNF/IFN-γ-induced proliferation or cytokine production. Proliferation was increased by TNF and further enhanced by the addition of IFN-γ. In co-culture experiments, SF stimulated with TNF/IFN but not TNF or IFN-γ alone increased shedding of VCAM-1 and expression of membrane TGFβ, which was associated with reduced survival of murine B cells. IFN-γ and TNF regulate the expression of TNF family member cytokines and associated receptors. Ligation of IFN-γR and Fn14 under pro-inflammatory conditions modulated IL-6/IL-8 production and proliferation. In B cell/SF co-cultures, the combination of TNF/IFN reduced B cell survival possibly via enhanced VCAM-1 shedding and/or increased TGF-β production. IFN-γ is necessary for the observed effects on B cell survival and SF cytokine production and emphasizes its anti-inflammatory role in rheumatoid arthritis.

The Schistosoma mansoni tegumental allergen protein, SmTAL1: Binding to an IQ-motif from a voltage-gated ion channel and effects of praziquantel

SmTAL1 is a calcium binding protein from the parasitic worm, Schistosoma mansoni. Structurally it is comprised of two domains – an N-terminal EF-hand domain and a C-terminal dynein light chain (DLC)-like domain. The protein has previously been shown to interact with the anti-schistosomal drug, praziquantel (PZQ). Here, we demonstrated that both EF-hands in the N-terminal domain are functional calcium ion binding sites. The second EF-hand appears to be more important in dictating affinity and mediating the conformational changes which occur on calcium ion binding. There is positive cooperativity between the four calcium ion binding sites in the dimeric form of SmTAL1. Both the EF-hand domain and the DLC-domain dimerise independently suggesting that both play a role in forming the SmTAL1 dimer. SmTAL1 binds non-cooperatively to PZQ and cooperatively to an IQ-motif from SmCav1B, a voltage-gated calcium channel. PZQ tends to strengthen this interaction, although the relationship is complex. These data suggest the hypothesis that SmTAL1 regulates at least one voltage-gated calcium channel and PZQ interferes with this process. This may be important in the molecular mechanism of this drug. It also suggests that compounds which bind SmTAL1, such as six from the Medicines for Malaria Box identified in this work, may represent possible leads for the discovery of novel antagonists.

Structures of cofilin-induced structural changes reveal local and asymmetric perturbations of actin filaments.

Members of the cofilin/ADF family of proteins sever actin filaments, increasing the number of filament ends available for polymerization or depolymerization. Cofilin binds actin filaments with positive cooperativity, forming clusters of contiguously bound cofilin along the filament lattice. Filament severing occurs preferentially at boundaries between bare and cofilin-decorated (cofilactin) segments and is biased at 1 side of a cluster. A molecular understanding of cooperative binding and filament severing has been impeded by a lack of structural data describing boundaries. Here, we apply methods for analyzing filament cryo-electron microscopy (cryo-EM) data at the single subunit level to directly investigate the structure of boundaries within partially decorated cofilactin filaments. Subnanometer resolution maps of isolated, bound cofilin molecules and an actin-cofilactin boundary indicate that cofilin-induced actin conformational changes are local and limited to subunits directly contacting bound cofilin. An isolated, bound cofilin compromises longitudinal filament contacts of 1 protofilament, consistent with a single cofilin having filament-severing activity. An individual, bound phosphomimetic (S3D) cofilin with weak severing activity adopts a unique binding mode that does not perturb actin structure. Cofilin clusters disrupt both protofilaments, consistent with a higher severing activity at boundaries compared to single cofilin. Comparison of these structures indicates that this disruption is substantially greater at pointed end sides of cofilactin clusters than at the barbed end. These structures, with the distribution of bound cofilin clusters, suggest that maximum binding cooperativity is achieved when 2 cofilins occupy adjacent sites. These results reveal the structural origins of cooperative cofilin binding and actin filament severing.

Structural Insights into the Intracellular Region of the Human Magnesium Transport Mediator CNNM4.

The four member family of “Cyclin and Cystathionine β-synthase (CBS) domain divalent metal cation transport mediators”, CNNMs, are the least-studied mammalian magnesium transport mediators. CNNM4 is abundant in the brain and the intestinal tract, and its abnormal activity causes Jalili Syndrome. Recent findings show that suppression of CNNM4 in mice promotes malignant progression of intestinal polyps and is linked to infertility. The association of CNNM4 with phosphatases of the regenerating liver, PRLs, abrogates its Mg2+-efflux capacity, thus resulting in an increased intracellular Mg2+ concentration that favors tumor growth. Here we present the crystal structures of the two independent intracellular domains of human CNNM4, i.e., the Bateman module and the cyclic nucleotide binding-like domain (cNMP). We also derive a model structure for the full intracellular region in the absence and presence of MgATP and the oncogenic interacting partner, PRL-1. We find that only the Bateman module interacts with ATP and Mg2+, at non-overlapping sites facilitating their positive cooperativity. Furthermore, both domains dimerize autonomously, where the cNMP domain dimer forms a rigid cleft to restrict the Mg2+ induced sliding of the inserting CBS1 motives of the Bateman module, from a twisted to a flat disk shaped dimer.

Protein Amphipathic Helix Insertion: A Mechanism to Induce Membrane Fission.

One of the fundamental features of biomembranes is the ability to fuse or to separate. These processes called respectively membrane fusion and fission are central in the homeostasis of events such as those related to intracellular membrane traffic. Proteins that contain amphipathic helices (AHs) were suggested to mediate membrane fission via shallow insertion of these helices into the lipid bilayer. Here we analyze the AH-containing proteins that have been identified as essential for membrane fission and categorize them in few subfamilies, including small GTPases, Atg proteins, and proteins containing either the ENTH/ANTH- or the BAR-domain. AH-containing fission-inducing proteins may require cofactors such as additional proteins (e.g., lipid-modifying enzymes), or lipids (e.g., phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2], phosphatidic acid [PA], or cardiolipin). Both PA and cardiolipin possess a cone shape and a negative charge (−2) that favor the recruitment of the AHs of fission-inducing proteins. Instead, PtdIns(4,5)P2 is characterized by an high negative charge able to recruit basic residues of the AHs of fission-inducing proteins. Here we propose that the AHs of fission-inducing proteins contain sequence motifs that bind lipid cofactors; accordingly (K/R/H)(K/R/H)xx(K/R/H) is a PtdIns(4,5)P2-binding motif, (K/R)x6(F/Y) is a cardiolipin-binding motif, whereas KxK is a PA-binding motif. Following our analysis, we show that the AHs of many fission-inducing proteins possess five properties: (a) at least three basic residues on the hydrophilic side, (b) ability to oligomerize, (c) optimal (shallow) depth of insertion into the membrane, (d) positive cooperativity in membrane curvature generation, and (e) specific interaction with one of the lipids mentioned above. These lipid cofactors favor correct conformation, oligomeric state and optimal insertion depth. The most abundant lipid in a given organelle possessing high negative charge (more negative than −1) is usually the lipid cofactor in the fission event. Interestingly, naturally occurring mutations have been reported in AH-containing fission-inducing proteins and related to diseases such as centronuclear myopathy (amphiphysin 2), Charcot-Marie-Tooth disease (GDAP1), Parkinson’s disease (α-synuclein). These findings add to the interest of the membrane fission process whose complete understanding will be instrumental for the elucidation of the pathogenesis of diseases involving mutations in the protein AHs.