Three dimensional structure of the light-harvesting chlorophyll a/b protein complex from plant chloroplasts

The light-harvesting chlorophyll a/b protein complex (LHC-II) is the major collector of solar energy in all plants and it binds about half of the chlorophyll in green plants. LHCII is a trimer in the photosynthetic membrane; each monomer consists of 232 amino acids, binds and orients a minimum of 12 chlorophyll molecules and three caroteinoids (two luteins and one neoxanthin) for light-harvesting and energy transfer. Although, the structure of LHC-II has been determined at 3.4 Å resolution by electron microscopy of two-dimensional crystals (Kühlbrandt et al., 1994), this is not sufficient to allow a complete understanding of the mechanism of energy transfer from LHC-II to the reaction centre, since the effective resolution in the z dimension is 4.9 Å. In fact, the chemical difference between Chl a and Chl b, which has a formyl group instead of the methyl group at the 7-position in the chlorin ring, is too small to be detected at this level of resolution. In addition, the orientation of the chlorophyll tetrapyrroles have not been determined unambiguously. This information is essential for a detailed understanding of the energy transfer within the complex and to the reaction centres of photosystem II and I (PSII and PSI). X-ray crystallography of three dimensional (3D) crystals may yield a more complete structure at high resolution. 3D crystals have been grown from LHC-II isolated from pea leaves using a standard purification procedure (Burke et al., 1978). The thylakoid membranes are solubilised in Triton X-100 and further purified by sucrose gradient ultra centrifugation. The LHC-II fraction is salt precipitated and pellets resuspended at the chlorophyll a/b ratio 2.8 mg/ml in 0.9 % Nonyl-glucoside. Crystals are currently obtained by vapour diffusion in hanging drops. These crystals are thin hexagonal plates, have a fairly large unit cell and diffract quite weakly. The high level of the background is due both to the detergent, necessary for protein solubilisation, and lipids, required for the trimer and crystals formation. However, three data sets, each from one single crystal have been collected up to 3.2 Å resolution over a rotation range of 135°. The crystals were exposed to a very highly collimated and brilliant beam (ID-14 EH1 at ESRF, Grenoble, France) and were kept under a stream of cold nitrogen to prevent radiation damage. Data were successfully integrated using the program XDS by Kabsch (1993). The crystals were found to belong to the space group P6 22 3 and have unit cell dimensions of a=128.45, b=128.45, c=135.32, a= ß=90º, ?=120. The solution of the phase problem was tackled by molecular replacement using, as a search model, the LHC-II structure solved by electron cryo-microscopy studies of twodimensional crystals (Kühlbrandt et al. 1994). Three different programs were tested: the most used AMoRe (Navaza et al., 1994) and the brute force based program Brute (FujinagaDer Chlorophyll a und b bindende Lichtsammelkomplex II (LHC-II) ist der Hauptantennenkomplex höherer Pflanzen. Er dient der Lichtabsorption und Energieweiterleitung und bindet fast die Hälfte der Chlorophylle in grünen Pflanzen. In der Thylakoidmembran liegt LHC-II als Trimer vor. Jedes Monomer besteht aus 232 Aminosäuren und bindet spezifisch mindestens 12 Chlorophyllmoleküle (Chl) und drei Carotinoide (zwei Luteine und ein Neoxanthin). Die Struktur von LHC-II wurde mittels Elektronenmikroskopie anhand von zweidimensionalen Kristallen mit einer Auflösung von 3.4 Å bestimmt. Diese Auflösung reicht jedoch nicht aus, um den Energieübertragungsmechanismus von LHC-II zu Photosystem II (PSII) zu verstehen, besonders da die tatsächliche Auflösung in der z- Dimension nur 4.9 Å beträgt. Der chemische Unterschied zwischen Chl a und Chl b besteht aus einer Formylgruppe anstelle einer Methylgruppe an der siebten Stelle des Chlorin-Rings und ist zu gering, um bei dieser Auflösung sichtbar zu werden. Zudem ist die Orientierung der Phorphyrinringe der Chlorophylle nicht eindeutig zu bestimmen. Diese Kenntnis ist jedoch wichtig für ein detailliertes Verständnis der Energieübertragung innerhalb des Komplexes und auf die Reaktionszentren von PSI und PSII. Um die Auflösung der Struktur zu verbessern und die EM Daten zu vervollständigen wurde Röntgenkristallographie an dreidimensionalen Kristallen (3D) durchgeführt. LHC-II wurde nach einem Standardprotokoll (Burge et al. 1978) aufgereinigt. Die in Triton X-100 solubilisierten Thylakoidmembranen wurden mittels eines linearen Saccharosegradienten aufgetrennt. Die fluoreszierende LHC-II Bande wurde mit KCl präzipitiert, gewaschen und in Nonyl-glucosid aufgenommen. Die Kristalle wurden mittels Dampfdiffusion in hängenden Tropfen erzeugt. Die Kristalle waren dünne hexagonale Platten, welche eine verhältnismäßig große Einheitszelle aufwiesen und schwach beugten. Die Kristalle waren zwischen 0.3 bis 0.4 mm groß und 10 bis 20 µm dick. Der hohe Hintergrund beruhte sowohl auf der Verwendung von Detergenz zur Solubilisierung des Proteins, als auch auf in der Präparation vorhandenen Lipiden. LHC- II bindet verschiedene Lipide: SQDG, MGDG, DGDG, PG und PC. Wie frühere Arbeiten gezeigt haben sind DGDG und PG für die 3D Kristallisation (Nußberger, 1994) notwendig, weshalb auf eine Entfernung der Lipide vor der Kristallisation verzichtet wurde. Die Datenaufnahme erfolgte an gefrorenen Kristallen um Strahlungsschäden zu verringern. Dies ermöglichte einen kompletten Datensatz über einen Rotationsbereich von 135º von einem einzelnen Kristall aufzunehmen. Insgesamt wurden 3 Datensätze mittels eines hoch kollimierten und brillianten Strahls (ID-14 EH1 am ESRF, Grenoble, Frankreich) mit einer Auflösung bis 3.2 Å aufgenommen. Die Datenanalyse erfolgte mittels des Programms XDS von Kabsch (1993). Dieses Programm verwendet einen R-faktor ( Rmrgd F . ) wie er in Diederich

The female coach in the world of collegiate sport: Accommodation and resistance to the dominant sport culture

This research explores the nature and meaning of collegiate coaching as an occupation for women and the extent to which women coaches accommodate to and resist the dominant sport culture. This study includes a brief historical analysis of the roots of coaching as an occupation for women and the emergence and nature of the female model of sport. To further explore the nature and meaning of coaching and the extent of accommodation and resistance to the dominant sport culture, forty-six (46) in-depth interviews were conducted with women collegiate coaches currently employed at an NCAA affiliated institution. A brief survey and field observations were additional sources of data. The findings of this research indicate that the occupational ideals of women coaches reflect the norms and values of the female model of sport, a model which emphasizes collegiate sport as an educational endeavor and the overall growth and welfare of student-athletes, and that their coaching practices reflect these same norms and values. This female model approach to coaching is conditioned, in part, by occupational socialization, gender socialization, and the nature and needs of female athletes. Findings further indicate that women both resist and accommodate to the dominant sport culture, a sport culture which reflects the influences of rationalization, capitalism, and patriarchy. Coaches in Division I, II were more likely than those in Division III to accommodate in practice to the dominant sport culture; and new coaches were more likely to accommodate than those in the old or established cohorts. A cultural studies approach was used to show that in the realm of sport, hegemony is never final; subordinate groups resist dominant meanings and struggle to control their sport experiences. This approach was combined with an adaptation of Bourdieu\u27s structural constructivism to show that while actors actively construct their social worlds, objective social structures condition and constrain practices and meanings. The objective structures of gender and work were shown here to condition and constrain the nature and meaning of coaching, and the nature and extent of women coaches\u27 accommodation and resistance to the dominant sport culture. In applying these theories to research findings, I conclude that the sub-culture of norms, values, and practices among women coaches functions as a form of collective resistance to the dominant sport culture. Women coaches are, in effect, social carriers of a residual sport form, the female model of sport. Their resistance influences the shape of, but does not transform, the dominant sport culture; and reflects the constraints imposed by patriarchy

Os Tambores Não Calam: Candombe e os novos ethos militantes no espaço público de Buenos Aires

En las últimas dos décadas, en la ciudad de Buenos Aires se viene presenciando un notable crecimiento y popularidad de distintas artes performáticas afrolatinoamericanas, siendo el candombe afrouruguayo el que tiene mayor presencia en el espacio público. Habiendo trascendido la comunidad migrante afrouruguaya que lo relocalizó en la década de 1970, hoy es parte de la cultura juvenil de numerosas ciudades del país. Este artículo aborda cómo las resignificaciones al interior de este desarrollo vigoroso se intersectan con otros procesos sociales locales contemporáneos. Focaliza la resignificación del candombe como "resistencia" a partir de un colectivo de tambores y danza -Los Tambores No Callan- en el que se explicita la conexión entre la performance del candombe y la política en tanto lucha social. Propone que esta práctica cultural forma parte de y da forma a, nuevos ethos militantes en el espacio público de Buenos Aires, la históricamente pretendida ciudad "blanca- europea.In the past two decades, Buenos Aires has witnessed a surprising growth and popularity of Afro-Latin American cultural practices. Foremost among them, and most visible in the city's public space, is Afro-Uruguayan candombe. Having spread beyond the Uruguayan immigrant community that contributed to its re-localization in the 1970s, it is nowadays widely part of the youth urban culture along the country. The paper discusses the re-significations following this vigorous development and how it intersects with other social processes of contemporary Argentine society. Focusing on the re-signification of candombe as "resistance", as performed by a collective of drummers and dancers known as "Los Tambores No Callan" (Drums cannot be silenced), it highlights the connections they establish between this cultural practice and politics as social struggle. It suggests that this cultural practice is part of -and helps shape- new activist ethos in the public space of Buenos Aires, a historically alleged "White" and "European" city.Nas últimas décadas, vem se presenciando na cidade de Buenos Aires um crescimento popular e notável de distintas artes performáticas afro-latino-americanas, sendo o candombe afro-uruguaio o que tem maior presença no espaço público. Tendo transcendido além da comunidade migrante afro-uruguaia que o localizou novamente na década de 1970, faz parte hoje da cultura juvenil de numerosas cidades do país. Este artigo aborda como as ressignificações ao interior deste desenvolvimento vigoroso se interceptam com outros processos sociais locais contemporâneos. Focaliza-se na ressignificação do candombe como "resistência" a partir de um coletivo de tambores e dança -Os Tambores Não Calam- no qual se explícita a conexão entre a performance do candombe e a política enquanto luta social. Propõe-se que esta prática cultural componha e modele novos ethos militantes no espaço público de Buenos Aires: uma cidade historicamente assumida como "branca e europeia".Fil: Lamborghini Torrecillas, Eva Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto de Historia Argentina y Americana ; Argentin

Os Tambores Não Calam: Candombe e os novos ethos militantes no espaço público de Buenos Aires

En las últimas dos décadas, en la ciudad de Buenos Aires se viene presenciando un notable crecimiento y popularidad de distintas artes performáticas afrolatinoamericanas, de las cuales el candombe afrouruguayo es el que tiene mayor presencia en el espacio público. Habiendo trascendido la comunidad migrante afrouruguaya que lo relocalizó en la década de 1970, hoy es parte de la cultura juvenil de numerosas ciudades del país. Este artículo aborda cómo las resignificaciones al interior de este desarrollo vigoroso se intersectan con otros procesos sociales locales contemporáneos. Focaliza la resignificación del candombe como “resistencia” a partir de un colectivo de tambores y danza –Los tambores no callan‒ en el que se explicita la conexión entre la performance del candombe y la política en tanto lucha social. Propone que esta práctica cultural forma parte de ‒y da forma a‒ nuevos ethos militantes en el espacio público de Buenos Aires, la históricamente pretendida “ciudad blanca-europea”.In the past two decades, Buenos Aires has witnessed a surprising growth and popularity of Afro-Latin American cultural practices. Foremost among them, and most visible in the city’s public space, is Afro-Uruguayan candombe. Having spread beyond the Uruguayan immigrant community that contributed to its re-localization in the 1970s, it is nowadays widely part of the youth urban culture along the country. The paper discusses the re-significations following this vigorous development and how it intersects with other social processes of contemporary Argentine society. Focusing on the re-signification of candombe as “resistance”, as performed by a collective of drummers and dancers known as “Los Tambores No Callan” (Drums cannot be silenced), it highlights the connections they establish between this cultural practice and politics as social struggle. It suggests that this cultural practice is part of –and helps shape– new activist ethos in the public space of Buenos Aires, a historically alleged “White” and “European” city.Nas últimas décadas, vem se presenciando na cidade de Buenos Aires um crescimento popular e notável de distintas artes performáticas afro-latino-americanas, sendo o candombe afro-uruguaio o que tem maior presença no espaço público. Tendo transcendido além da comunidade migrante afro-uruguaia que o localizou novamente na década de 1970, faz parte hoje da cultura juvenil de numerosas cidades do país. Este artigo aborda como as ressignificações ao interior deste desenvolvimento vigoroso se interceptam com outros processos sociais locais contemporâneos. Focaliza-se na ressignificação do candombe como “resistência” a partir de um coletivo de tambores e dança –Os Tambores Não Calam– no qual se explícita a conexão entre a performance do candombe e a política enquanto luta social. Propõe-se que esta prática cultural componha e modele novos ethos militantes no espaço público de Buenos Aires: uma cidade historicamente assumida como “branca e europeia”

Antropología de los museos y representaciones afrodescendientes: perspectivas teóricas, debates y propuestas

Fuertemente vinculada a la consolidación de los Estados nacionales modernos y al colonialismo, la configuración del museo fue central para la clasificación de identidades y “culturas nacionales” homogéneas, así como para la exclusión de “otros” (externos e internos). En contraposición, y en consonancia con los nuevos contextos multiculturalistas, de reivindicaciones y demandas en términos de etnicidad y luchas de distintas minorías sociales por sus derechos, se espera que los museos actuales puedan dar lugar a una diversidad de identidades silenciadas y/o representadas históricamente desde cánones hegemónicos. Este artículo propone un recorrido sobre la bibliografía crítica de los museos de las últimas décadas, distinguiendo aportes desde la Antropología que dan cuenta de la transformación de estas instituciones en arenas altamente politizadas, donde grupos subalternizados cuestionan las relaciones de poder históricas y dirimen su inclusión y auto-representación. El trabajo finaliza enfocando las representaciones afrodescendientes en Argentina como un terreno particularmente relevante para reflexionar sobre la supuesta transparencia de las relaciones entre cultura, identidad y museos

Uruguayan candombe in Buenos Aires: (Proposing) New urban imaginaries in the “White” city

El trabajo se propone examinar la apropiación de espacios públicos y la generación de nuevos imaginarios y representaciones urbanas a través de prácticas culturales populares. Para ello nos focalizaremos en el desarrollo y expansión espacial del candombe (de origen uruguayo). La reterritorialización de esta práctica musical requiere en un primer momento de su anclaje en el casco histórico de la ciudad y de la apelación a la memoria de presencia negra en ese lugar. Tanto esta referencia como la posterior expansión de la práctica por otros barrios implican un trabajo de imaginación de la ciudad que discute la imagen dominante de Buenos Aires como blanca, moderna y europea. Al desafiar esta imagen, proponiendo un imaginario urbano alternativo, los candomberos entran en conflicto con distintos agentes y actores sociales.The paper examines the appropriation of public space and the proposal of new urban imaginaries by the practitioners of popular cultural practices. We focus on the development and spatial expansion of Afro-Uruguayan candombe in Buenos Aires. The reterritorialization of this musical practice requires at first embedding it in the historical neighborhood of the city and appealing to the memory of Black presence in the area. The reference to this memory, and the ulterior expansion of candombe to other neighborhoods, imply a work of imagining the city that challenges the dominant image of Buenos Aires as White, modern and European. Defying this image and proposing alternative urban imaginaries, practitioners of candombe establish conflictive interactions with different social agents and actors

PROCESOS DE REAFRICANIZACIÓN EN LA SOCIEDAD ARGENTINA: umbanda, candombe y militancia "afro"

En las últimas dos décadas, la sociedad argentina – considerada entre las más “europeas” y “blancas” del continente- ha experimentado un importante desarrollo de manifestaciones culturales afro-americanas. Las religiones afro-brasileras (Umbanda, Batuque, Quimbanda) se  han convertido en una opción atractiva para vastos sectores medio-bajos y -sobre todo- populares en el Gran Buenos Aires. El candombe afro-uruguayo dejó de ser una manifestación cultural de inmigrantes, como fue a fines de la década de 1980, y actualmente forma parte de la cultura juvenil porteña. Los afro-argentinos, invisibilizados durante casi un siglo, han comenzado a reclamar por sus derechos y han logrado incluir una pregunta sobre afrodescendencia en el censo nacional de población 2010. El trabajo examina el rol de una cada vez más aceptada narrativa multicultural de la nación en la creación de una estructura de oportunidades que permite estos desarrollos. Discute, asimismo, los roles de las variables religión, nación y raza en su desigual recepción por parte de la sociedad.Palabras clave: Raza. Nación. Religión. Multiculturalismo.ABSTRACTIn the past decade, Argentine society, considered to be the most “European” and “white” society in the continent, has experienced an important development of Afro-American cultural phenomena. Afro-Brazilian religions (Umbanda, Batuque, Quimbanda) have become an attractive alternative for lower/middle and working-class sectors in the Greater Buenos Aires area. Afro-Uruguayan candombe stopped being an exclusively immigrant cultural endeavor, as it was at the end of the 1980s, and has become part of the “porteño” youth culture. Afro-Argentines, invisibilized for almost a century, have started to demand their civic rights and managed to include a question about African descendency in the 2010 national population census. The paper explores the role of an increasingly accepted multicultural narrative of the city of Buenos Aires in the creation of an opportunity structure that allows for these developments. At the same time, it discusses the roles of variables such as religion, nation and race in their uneven reception by society.Keywords: Race. Nation. Religion. Multiculturalism

Estudos afrodescendentes na Argentina: novas perspectivas e desafios em um país «sem raças»

En Argentina, la narrativa de blanquitud y europeidad y el discurso de la «desaparición» afroargentina instituyeron un mito de origen de la nación cuyos efectos persisten. En las últimas décadas, sin embargo, la renovación y consolidación de un campo interdisciplinario de estudios y reflexión sobre afrodescendencia se ha nutrido de, y ha contribuido a, la «revisibilización» y al (re)conocimiento de un sector de la población invisibilizado y marginado. En este artículo revisaremos los avances y desafíos de los estudios sobre afrodescendencia en Argentina, distinguiendo algunos campos problemáticos y destacando aportes, debates y vacancias. Pondremos en perspectiva los estudios de categorías racializadas en la colonia y tiempos republicanos -primero-, y durante la consolidación del estado moderno y hasta el presente -luego-, para finalmente dar cuenta de abordajes sobre movimientos políticos, migraciones y resignificaciones performáticas. Esta mirada panorámica problematiza el supuesto lugar «novedoso» de este campo de estudios y sus particularidades en un país que se considera «sin razas».In Argentina, the narratives of whiteness and Europeanness, along with the discourse of Afro-Argentinean “disappearance” helped institute a myth of origin of the nation, whose effects remain. In the last few decades, however, the renewal and consolidation of an interdisciplinary field of studies and reflection on Afro-descendence has been fed by and helped to “revisibilizing” and (re)acknowledge a population group previously invisibilized and marginalized. In this paper, we will review the advances and challenges of the studies on African descent in Argentina, distinguishing several challenging fields and highlighting contributions, debates, and gaps. We will examine a new angle of the studies of racialized categories during the Colony and the Republican era, in the first place, and during the consolidation of modern State up to the present time, next. Finally, we will account for approaches on political movements, migrations and performative resignifications. This overview challenges the supposedly “novel” place of this field of studies and its particularities in a country typically considered as “raceless”.Na Argentina, a narrativa da branquitude e da europeidade e o discurso do «desaparecimento» afro-argentino instituíram um mito de origem da nação cujos efeitos persistem. No entanto, nas últimas décadas, a renovação e consolidação de um campo interdisciplinar de estudos e reflexão sobre a afro-descendência tem sido alimentada pela «revisibilização» e o (re) conhecimento de um setor da população invisibilizado e marginalizado. Neste artigo, analisaremos os avanços e desafios dos estudos sobre afro-descendência na Argentina, distinguindo alguns campos problemáticos e destacando contribuições, debates e vazios. Vamos colocar em perspectiva os estudos de categorias racializadas na Colônia e na República -primeiro- e durante a consolidação do Estado moderno e até o presente -depois-, para finalmente evidenciar abordagens sobre movimentos políticos, migrações e resignificações performativas. Essa visão panorâmica problematiza a suposta «novidade» desse campo de estudos e suas particularidades em um país que se considera «sem raças».Fil: Lamborghini Torrecillas, Eva Lucia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto de Historia Argentina y Americana ; ArgentinaFil: Geler, Lea Natalia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto de Historia Argentina y Americana ; ArgentinaFil: Guzman, Maria Florencia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Saavedra 15. Instituto de Historia Argentina y Americana ; Argentin