Mechanistic insights into G-protein coupling with an agonist-bound G-protein-coupled receptor.

G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by promoting guanine nucleotide exchange. Here, we investigate the coupling of G proteins with GPCRs and describe the events that ultimately lead to the ejection of GDP from its binding pocket in the Gα subunit, the rate-limiting step during G-protein activation. Using molecular dynamics simulations, we investigate the temporal progression of structural rearrangements of GDP-bound Gs protein (Gs·GDP; hereafter GsGDP) upon coupling to the ß2-adrenergic receptor (ß2AR) in atomic detail. The binding of GsGDP to the ß2AR is followed by long-range allosteric effects that significantly reduce the energy needed for GDP release: the opening of α1-αF helices, the displacement of the αG helix and the opening of the α-helical domain. Signal propagation to the Gs occurs through an extended receptor interface, including a lysine-rich motif at the intracellular end of a kinked transmembrane helix 6, which was confirmed by site-directed mutagenesis and functional assays. From this ß2AR-GsGDP intermediate, Gs undergoes an in-plane rotation along the receptor axis to approach the ß2AR-Gsempty state. The simulations shed light on how the structural elements at the receptor-G-protein interface may interact to transmit the signal over 30 Å to the nucleotide-binding site. Our analysis extends the current limited view of nucleotide-free snapshots to include additional states and structural features responsible for signaling and G-protein coupling specificity.

Time-resolved cryo-EM of G-protein activation by a GPCR.

G-protein-coupled receptors (GPCRs) activate heterotrimeric G proteins by stimulating guanine nucleotide exchange in the Gα subunit1. To visualize this mechanism, we developed a time-resolved cryo-EM approach that examines the progression of ensembles of pre-steady-state intermediates of a GPCR-G-protein complex. By monitoring the transitions of the stimulatory Gs protein in complex with the ß2-adrenergic receptor at short sequential time points after GTP addition, we identified the conformational trajectory underlying G-protein activation and functional dissociation from the receptor. Twenty structures generated from sequential overlapping particle subsets along this trajectory, compared to control structures, provide a high-resolution description of the order of main events driving G-protein activation in response to GTP binding. Structural changes propagate from the nucleotide-binding pocket and extend through the GTPase domain, enacting alterations to Gα switch regions and the α5 helix that weaken the G-protein-receptor interface. Molecular dynamics simulations with late structures in the cryo-EM trajectory support that enhanced ordering of GTP on closure of the α-helical domain against the nucleotide-bound Ras-homology domain correlates with α5 helix destabilization and eventual dissociation of the G protein from the GPCR. These findings also highlight the potential of time-resolved cryo-EM as a tool for mechanistic dissection of GPCR signalling events.

Presentación de un paciente con neurocisticercosis / Presentation of a Patient with Neurocysticercosis

La cisticercosis es la más frecuente e importante de las enfermedades causadas por parásitos en el sistema nervioso del hombre y constituye un problema de salud pública de inmensa magnitud. Se presentó un paciente de 65 años, trabajador de la Empresa Cárnica de Holguín el cual ingiere carne de cerdo cruda, y sangre de novillo, es llevado al Cuerpo de Guardia de Medicina Interna del Hospital General Universitario Vladimir Ilich Lenin de la provincia de Holguín, Cuba, por disminución de la fuerza muscular del hemicuerpo izquierdo. Se diagnosticó neurocisticercosis activa por los antecedentes y se confirmó con estudios de neuroimágenes (tomografía computarizada).

Cysticercosis is the most common and significant parasites borne disease of the nervous system of man and represents a public health problem of immense magnitude. A 65- year- old male patient, worker of Meat Company of Holguin which ingested raw porkmeat and blood, was brought to the Internal Medicine emergency ward, of "Vladimir Ilich Lenin" General University Hospital, Holguin Province, Cuba, complaining of lack of muscle strength of the left side of the body. Active neurocysticercosis was diagnosed by history and confirmed by neuroimaging studies: computed tomography and nuclear magnetic resonance.

Presentación de un paciente con neurocisticercosis / Presentation of a Patient with Neurocysticercosis

La cisticercosis es la más frecuente e importante de las enfermedades causadas por parásitos en el sistema nervioso del hombre y constituye un problema de salud pública de inmensa magnitud. Se presentó un paciente de 65 años, trabajador de la Empresa Cárnica de Holguín el cual ingiere carne de cerdo cruda, y sangre de novillo, es llevado al Cuerpo de Guardia de Medicina Interna del Hospital General Universitario Vladimir Ilich Lenin de la provincia de Holguín, Cuba, por disminución de la fuerza muscular del hemicuerpo izquierdo. Se diagnosticó neurocisticercosis activa por los antecedentes y se confirmó con estudios de neuroimágenes (tomografía computarizada). (AU)

Cysticercosis is the most common and significant parasites borne disease of the nervous system of man and represents a public health problem of immense magnitude. A 65- year- old male patient, worker of Meat Company of Holguin which ingested raw porkmeat and blood, was brought to the Internal Medicine emergency ward, of "Vladimir Ilich Lenin" General University Hospital, Holguin Province, Cuba, complaining of lack of muscle strength of the left side of the body. Active neurocysticercosis was diagnosed by history and confirmed by neuroimaging studies: computed tomography and nuclear magnetic resonance.(AU)

Hipertensión arterial secundaria a hipoplasia tubular aórtica extensa en una adolescente con neurofibromatosis 1 / Arterial hypertension after extensive tubular aortic hypoplasia in an adolescent with Neurofibromatosis 1

Se presenta el caso de una adolescente de 19 años, que en un examen de rutina evidenció cifras de tensión arterial de 220/120 mmHg. Al examen físico, tenía baja talla, en la piel manchas café con leche, neurofibromas, pecas axilares, hipotrofia del miembro superior izquierdo, con debilidad y retardo del pulso radial. Ambos pulsos femorales eran imperceptibles. El fondo de ojo mostró una retinopatía hipertensiva grado II. En la radiografía de tórax, el botón aórtico estaba hipoplásico era evidente el signo de Roessler en la 3ra y 4ta costillas izquierdas. La ecocardiografía puso de manifiesto hipertrofia concéntrica del ventrículo izquierdo, en la urografía contrastada, el riñón izquierdo no captó el contraste. El estudio vascular contrastado mostró un neurofibroma sacro de 4 cm, la arteria subclavia izquierda estaba estenosada, y la aorta, a partir de ese nivel, muy estenosada de manera uniforme, con múltiples placas de ateroma, disminuyendo distalmente su calibre, ambas arterias ilíacas extremadamente finas. La arteria renal izquierda estaba estenosada y con abundante circulación colateral...(AU)

A 19-year old adolescent with neurofibromatosis 1 who showed very high records of arterial tension was attended at this service. The patient was very short with cafè au lait spot in the skin, neurofibroma, axillary freckles and hypotrophy of the left upper limb, with weakness and delay of the radial pulse of that side. Both femoral pulses were imperceptible. Fundus showed hypoplasic aortic bouton and there was Roessler`s sign in the 3rd and 4th left ribs. Echocardiography showed concentric hypertrophy of the left ventricle, and in the urography the left kidney did not get contrast. The vascular study showed sacral neurofibroma. The left subclavian artery was stenotic and the aortic artery had multiple atheromatous plaques...(AU)