Influence of the sterol aliphatic side chain on membrane properties: a molecular dynamics study

Following a recent experimental investigation of the effect of the length of the alkyl side chain in a series of cholesterol analogues (Angew. Chem., Int. Ed., 2013, 52, 12848–12851), we report here an atomistic molecular dynamics characterization of the behaviour of methyl-branched side chain sterols (iso series) in POPC bilayers. The studied sterols included androstenol (i-C0-sterol) and cholesterol (i-C8-sterol), as well as four other derivatives (i-C5, i-C10, i-C12 and i-C14-sterol). For each sterol, both subtle local effects and more substantial differential alterations of membrane properties along the iso series were investigated. The location and orientation of the tetracyclic ring system is almost identical in all compounds. Among all the studied sterols, cholesterol is the sterol that presents the best matching with the hydrophobic length of POPC acyl chains, whereas longer-chained sterols interdigitate into the opposing membrane leaflet. In accordance with the experimental observations, a maximal ordering effect is observed for intermediate sterol chain length (i-C5, cholesterol, i-C10). Only for these sterols a preferential interaction with the saturated sn-1 chain of POPC (compared to the unsaturated sn-2 chain) was observed, but not for either shorter or longer-chained derivatives. This work highlights the importance of the sterol alkyl chain in the modulation of membrane properties and lateral organization in biological membranes

Treatment interaction in moments of ambivalence: an exploratory study a case of failure

No processo psicoterapêutico a mudança constrói-se através da emergência e expansão de excepções ao funcionamento problemático do cliente. Contudo, o potencial de mudança destas excepções ou inovações pode ser abortado através da atenuação do seu significado quando o cliente as desvaloriza, trivializa ou nega. Quando este processo se repete ao longo da terapia estamos na presença de ambivalência, na medida em que ocorre uma oscilação recorrente entre duas posições opostas (inovação-retorno ao funcionamento problemático). O presente estudo exploratório tem como principal objectivo descrever a interacção terapêutica nestes momentos de ambivalência, num caso de insucesso psicoterapêutico, recorrendo ao Sistema de Codificação da Colaboração Terapêutica. Os resultados sugerem que a ambivalência emerge maioritariamente no seguimento de intervenções em que a terapeuta desafia a perspectiva habitual da cliente. Os resultados mostram ainda que a terapeuta tende a responder à ambivalência da cliente com um novo desafio, sendo que a cliente tende a expressar novamente ambivalência ou a discordar da terapeuta. Deste modo, quando a terapeuta persiste no desafio verifica-se frequentemente uma escalada no desconforto da cliente, que se manifesta na evolução de uma resposta de ambivalência para uma resposta de invalidação por parte da cliente.Change in psychotherapy occurs through the emergence and expansion of exceptions to the client’s problematic functioning. However, these exceptions’ potential to promote change may be aborted by the attenuation of their meaning, when the client devaluates, trivializes or denies them. When this process repeats itself throughout the therapeutic process, clients are facing ambivalence, since there is a recurrent oscillation between two opposite positions (innovation – return to the problematic functioning). The present exploratory study aims at describing the therapeutic interaction within moments in which ambivalence occurs in an unsuccessful case using the Therapeutic Collaboration Coding System. Results suggest that ambivalence emerges mainly as a response to an intervention in which the therapist challenges clients usual (i.e., problematic) perspective. Moreover, results suggest that the therapist tends to respond to client’s ambivalence with a new challenge intervention which is generally followed by ambivalence or even invalidation from the client. Hence, when the therapist persists in challenging the client there is usually an escalation in clients’ discomfort, expressed in the evolution of a ambivalence response towards an invalidation response.(undefined

Molecular Dynamics Simulation of HIV Fusion Inhibitor T-1249: Insights on Peptide-Lipid Interaction

T-1249 is a peptide that inhibits the fusion of HIV envelope with the target cell membrane. Recent results indicate that T-1249, as in the case of related inhibitor peptide T-20 (enfuvirtide), interacts with membranes, more extensively in the bilayer liquid disordered phase than in the liquid ordered state, which could be linked to its effectiveness. Extensive molecular dynamics simulations (100 ns) were carried out to investigate the interaction between T-1249 and bilayers of 1-palmitoyl-2-oleoyl-phosphatidylcholine (POPC) and POPC/cholesterol (1 : 1). It was observed that T-1249 interacts to different extents with both membrane systems and that peptide interaction with the bilayer surface has a local effect on membrane structure. Formation of hydrogen bonding between certain peptide residues and several acceptor and donor groups in the bilayer molecules was observed. T-1249 showed higher extent of interaction with bilayers when compared to T-20. This is most notable in POPC/Chol membranes, owing to more peptide residues acting as H bond donors and acceptors between the peptide and the bilayer lipids, including H-bonds formed with cholesterol. This behavior is at variance with that of T-20, which forms no H bonds with cholesterol. This higher ability to interact with membranes is probably correlated with its higher inhibitory efficiency

Therapeutic collaboration and resistance: describing the nature and quality of the therapeutic relationship within ambivalence events using the therapeutic collaboration coding system

We understand ambivalence as a cyclical movement between two opposing parts of the self. The emergence of a novel part produces an innovative moment, challenging the current maladaptive self-narrative. However, the novel part is subsequently attenuated by a return to the maladaptive self-narrative. This study focused on the analysis of the therapeutic collaboration in episodes in which a relatively poor-outcome client in narrative therapy expressed ambivalence. Method: For our analysis we used the Therapeutic Collaboration Coding System, developed to assess whether and how the therapeutic dyad is working within the therapeutic zone of proximal development (TZPD). Results: Results showed that when the therapist challenged the client after the emergence of ambivalence, the client tended to invalidate (reject or ignore) the therapist’s intervention. Conclusions: This suggests that in such ambivalence episodes the therapist did not match the client’s developmental level, and by working outside the TZPD unintentionally contributed to the maintaining the client’s ambivalence

Behaviour of NBD-head group labelled phosphatidylethanolamines in POPC bilayers: a molecular dynamics study

A complete homologous series of fluorescent phosphatidylethanolamines (diCnPE), labelled at the head group with a 7-nitrobenz-2-oxa-1,3-diazo-4-yl(NBD) fluorophore and inserted in 1-palmitoyl, 2-oleoyl-snglycero- 3-phosphocholine (POPC) bilayers, was studied using atomistic molecular dynamics simulations. The longer-chained derivatives of NBD-diCnPE, with n = 14, 16, and 18, are commercially available, and widely used as fluorescent membrane probes. Properties such as location of atomic groups and acyl chain order parameters of both POPC and NBD-diCnPE, fluorophore orientation and hydrogen bonding, membrane electrostatic potential and lateral diffusion were calculated for all derivatives in the series. Most of these probes induce local disordering of POPC acyl chains, which is on the whole counterbalanced by ordering resulting from binding of sodium ions to lipid carbonyl/glycerol oxygen atoms. An exception is found for NBD-diC16PE, which displays optimal matching with POPC acyl chain length and induces a slight local ordering of phospholipid acyl chains. Compared to previously studied fatty amines, acyl chain-labelled phosphatidylcholines, and sterols bearing the same fluorescent tag, the chromophore in NBD-diCnPE locates in a similar region of the membrane (near the glycerol backbone/carbonyl region) but adopts a different orientation (with the NO2 group facing the interior of the bilayer). This modification leads to an inverted orientation of the P–N axis in the labelled lipid, which affects the interface properties, such as the membrane electrostatic potential and hydrogen bonding to lipid head group atoms. The implications of this study for the interpretation of the photophysical properties of NBD-diCnPE (complex fluorescence emission kinetics, differences with other NBD lipid probes) are discussed

Avaliação de propriedades estruturais de membranas lipídicas após substituição do colesterol por análogos fluorescentes

A espectroscopia e a microscopia de fluorescência têm sido usadas em biofísica de membranas há décadas. Como a unidade estrutural básica das membranas biológicas é a bicamada de lípidos e estes não fluorescem, o uso de sondas extrínsecas de membrana é uma necessidade. Contudo, duas questões preocupantes se levantam quanto ao uso de sondas extrínsecas de fluorescência em estudos de membranas. Em primeiro lugar, o comportamento das moléculas de sonda na bicamada (que região da bicamada elas reportam, as suas dinâmicas translacional e rotacional) é frequentemente mal conhecido. Em segundo lugar, na interpretação de resultados de experiências de fluorescência, pode ser difícil distinguir entre propriedades legítimas da membrana e efeitos de perturbação resultantes da incorporação da sonda. Para este efeito, as simulações por dinâmica molecular (MD), ao providenciarem informação detalhada à escala atómica, representam um meio valioso para caracterizar a localização e dinâmica de sondas na bicamada, assim como a magnitude de perturbação que elas induzem na estrutura lipídica [1]. Neste contexto, optimizaram-se, com recurso ao programa Firefly, as estruturas do colesterol e de dois análogos fluorescentes (desidroergoesterol e colestatrienol) ao nível de teoria DFT/R-B3LYP/6-31G(d) e submeteram-se em seguida ao servidor de topologias ATB, inscrevendo simultaneamente as cargas parciais calculadas na topologia molecular. Estas topologias foram utilizadas na construção de modelos de membranas lipídicas constituídas por POPC, colesterol e uma das sondas fluorescentes acima identificadas. Os modelos assim obtidos foram hidratados e sujeitos a simulações de MD, donde se calculou a área por lípido, a espessura e densidade da bicamada, os coeficientes de difusão lateral para as espécies presentes e os parâmetros de ordem das cadeias acilo. As simulações foram efectuadas em ensemble NPT através do pacote de software GROMACS. Análises preliminares permitiram a comparação dos comportamentos na bicamada dos esteróis fluorescentes com o do colesterol, informação vital para validar o uso dos primeiros como análogos fluorescentes do segundo. REFERÊNCIAS [1] Loura, L.M.S.; Prates Ramalho, J.P. Biophys. Rev. 1 (2009), 141

Análise sensorial de cocada saborizada com polpa de maracujá do mato.

A produção de maracujá é de grande importância para a economia brasileira devido ao emprego intensivo de mão-de-obra, geração de renda e, principalmente, pela colheita continuada da safra ao longo do ano

Diagnóstico da ocorrência de abóbora e jerimum nos municípios de Juazeiro-BA e Petrolina-PE.

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