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Biochim Biophys Acta Biomembr ; 1861(1): 298-305, 2019 01.
Artigo em Inglês | MEDLINE | ID: mdl-29920238


Spectrin, a major component of the membrane skeletal meshwork of metazoan cells, is implicated to associate with membrane domains and is known to act as a scaffold for stabilization and activation of different signalling modules. We have studied the effect of GM1 (monosialotetrahexosyl ganglioside), a well-known model ganglioside and a signalling moiety, on the interaction of non-erythroid brain spectrin with both saturated and unsaturated aminophospholipids by spectroscopic methods. We observe that GM1 modulates brain spectrin-aminophospholipid interaction to the greatest degree whereas its effect on erythroid spectrin is not as pronounced. Fluorescence quenching studies show that brain spectrin interacts with DMPC/DMPE-based vesicles with a 10-fold increased affinity in presence of very low amounts of 2% and 5% GM1, and the extent of quenching decreases progressively in presence of increasing amounts of GM1. Interaction of brain spectrin with unsaturated membrane systems of DOPC/DOPE weakens in presence GM1. Increase in the mean lifetime of the Trp residues of brain spectrin in presence of GM1 indicates change in the microenvironment of spectrin, without affecting the secondary structure of the protein significantly. Studies on pressure - area isotherm of Langmuir-Blodgett monolayer and Brewster's angle microscopy show that GM1 has an expanding effect on the aminophospholipid monolayers, and ordered regions in DMPC/DMPE mixed monolayers are formed and are stabilized at higher pressure. GM1-induced fluidization of the phospholipid membranes and probable physical contact between bulky sugar head group of GM1 and spectrin, may explain the modulatory role of GM1 on aminophospholipid interactions with nonerythroid brain spectrin.

Encéfalo/metabolismo , Membrana Celular/química , Gangliosídeo G(M1)/química , Lipídeos/química , Oligossacarídeos/química , Espectrina/química , Triptofano/química , Animais , Dicroísmo Circular , Dimiristoilfosfatidilcolina/química , Cinética , Micelas , Fosfatidilcolinas/química , Fosfatidiletanolaminas/química , Pressão , Ligação Proteica , Ovinos , Espectrometria de Fluorescência , Temperatura
ACS Appl Mater Interfaces ; 10(20): 17409-17418, 2018 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-29697251


Luminescent materials possessing both the mechanoluminescence (MCL) and electroluminescence (EL) properties are the quest for sensing and optoelectronic applications. We report on the synthesis of a new tailor-made luminogen, 1,2-bis(4-(1-([1,1'-biphenyl]-4-yl)-2,2-diphenylvinyl)phenyl)-1,2-diphenylethene (TPE 5), using Suzuki coupling reaction with high yield. An aggregation-induced emission (AIE) active complex TPE 5 forms supramolecular spherical aggregates at the air-water interface of a Langmuir trough. As a consequence, a large enhancement of luminescence is obtained from the mono- and multilayer Langmuir-Blodgett films of TPE 5 owing to the AIE effect. The luminogen TPE 5 exhibits a reversible MCL response, displaying photoluminescence switching due to change in the crystalline states under external stimuli. The unique feature of luminescence enhancement upon aggregate formation is utilized for the fabrication of light-emitting diodes with low threshold voltage using supramolecular aggregates as the active layer. This work demonstrates an efficient strategy for obtaining controlled supramolecular aggregates of AIEgen with a potential in the dual applications of MCL and EL.

Adv Exp Med Biol ; 1112: 3-11, 2018.
Artigo em Inglês | MEDLINE | ID: mdl-30637686


Spectrin-based proteinaceous membrane skeletal network has been found to be implicated in membrane disorders like hereditary spherocytosis (HS). HS greatly affects eryptosis via loss of membrane asymmetry which is seen to be the case in haemoglobin disorders like thalassemia and sickle cell disease as well. The biological implications of the status of membrane asymmetry are strongly correlated to spectrin interactions with aminophospholipids, e.g. PE and PS. Fluorescence and X-ray reflectivity (XRR) measurements of spectrin interactions with small unilamellar vesicles (SUVs) and cushioned bilayers of phospholipids, respectively, were studied. Both the XRR and fluorescence measurements led to the characterization of spectrin orientation on the surface of lipid bilayer of phosphatidylcholine (PC) and PC/aminophospholipid mixed membrane systems showing formation of a uniform layer of spectrin on top of the mixed phospholipid bilayer. Fluorescence studies show that spectrin interacts with PC and phosphatidylethanolamine (PE)/phosphatidylserine (PS) membranes with binding dissociation constants (Kd) in the nanomolar range indicating the role of spectrin in the maintenance of the overall membrane asymmetry of erythrocytes.

Membrana Celular/química , Eritrócitos/citologia , Espectrina/química , Eriptose , Humanos , Bicamadas Lipídicas/química , Fosfolipídeos/química , Esferocitose Hereditária
J Phys Chem B ; 121(16): 4081-4090, 2017 04 27.
Artigo em Inglês | MEDLINE | ID: mdl-28383262


Lateral and out-of-plane organization of cholesterol and its effect on regulating the physicochemical properties of zwitterionic phospholipid model membranes have been investigated by a pressure-area isotherm study from the Langmuir monolayer, atomic force microscopy (AFM), and X-ray reflectivity (XRR) measurements from supported binary monolayer films. The systematic isotherm studies on the Langmuir monolayer of phospholipids and the subsequent extraction of excess Gibbs free energy (ΔGexc) revealed the mechanism of cholesterol interaction and the molecular cooperativeness for different arrangements in the phospholipid model membranes. We have found a critical cholesterol molar concentration (χc) up to which the lipid-cholesterol miscibility gradually increases and then further increase in the concentration leads to an inhomogeneous structure formation similar to raft structures. The thickening in the lipid acyl chain and the subsequent lowering of the lipid head group thickness up to χc are also evident from the XRR study. Beyond χc, large-sized domains are observed in the AFM images from the deposited monolayer. χc has also been observed to depend on the phase of the monolayer, in particular, ∼25 molar % in the gel phase and ∼40 molar % in the fluid phase, wherein a regular distribution has been found with the highest separation between the cholesterol molecules. The extracted isothermal compressibility coefficient (CS) and ΔGexc from the monolayer isotherms indicate that the molecular arrangement at χc are the most stable configurations of the monolayer. Our study provides direct evidence into cholesterol-induced evolution in phase behavior and the consequent model on the structure at different phases in the phospholipid Langmuir monolayers.

Colesterol/química , Membranas Artificiais , Fosfolipídeos/química , Interações Hidrofóbicas e Hidrofílicas , Microscopia de Força Atômica , Modelos Moleculares , Propriedades de Superfície , Termodinâmica , Difração de Raios X