Cryo-EM structure of a functional monomeric Photosystem I from Thermosynechococcus elongatus reveals red chlorophyll cluster

A high-resolution structure of trimeric cyanobacterial Photosystem I (PSI) from Thermosynechococcus elongatus was reported as the first atomic model of PSI almost 20 years ago. However, the monomeric PSI structure has not yet been reported despite long-standing interest in its structure and extensive spectroscopic characterization of the loss of red chlorophylls upon monomerization. Here, we describe the structure of monomeric PSI from Thermosynechococcus elongatus BP-1. Comparison with the trimer structure gave detailed insights into monomerization-induced changes in both the central trimerization domain and the peripheral regions of the complex. Monomerization-induced loss of red chlorophylls is assigned to a cluster of chlorophylls adjacent to PsaX. Based on our findings, we propose a role of PsaX in the stabilization of red chlorophylls and that lipids of the surrounding membrane present a major source of thermal energy for uphill excitation energy transfer from red chlorophylls to P700

Kırmızı Lahana Antosiyaninlerinin Mika Titanya Özel Etki Pigmentleri Üzerine Çöktürülmesi

Anthocyanin pigments extracted from Red Cabbage (Brassica oleracea) were deposited at different pH values on formerly synthesized mica-titania pigments after a purification step. Both anthocyanin pigments and mica/titania/anthocyanin pigments are investigated by using infrared, UV/VIS and fluorecence spectroscopies in order to understand the interactions of anthocyanins with the nano-titania surfaces. Anthocyanins have been considered as dye components in dye sensitized solar cells. The pH of the deposition medium was not investigated as a parameter in those studies and generally kept acidic (around a pH of 2-3). Therefore it was speculated that a dominant form of anthocyanin was deposited and responsible of the charge transfer reactions. It was reported that the lower the fluorescence, the higher would be the charge transfer efficieny. Here the effect of pH on structural transformations of anthocyanins was investigated with a reference to their interaction with the rutile nano-titania Surfaces in the deposition medium. The fluorecence of the combination pigments at higher pH values was lower compared to those of at lower pH values, due to the quenching effect among different forms. It can be proposed that a control on pH of the deposition medium can improve the cell efficiencies.Kırmızı lahanadan elde edilen antosiyanin pigmentleri, bir saflaştırma adımının ardından, farklı pH değerlerinde daha önceden üretilmiş olan mika titanya pigmentlerinin üzerine çöktürülmüştür. Hem antosiyanin pigmentleri, hem de mika titanya antosiyanin kombinasyon pigmentleri kızılötesi, UV-görünür bölge ve Flüoresans Spektrometrisi yöntemleri ile incelenmiştir.Antosiyanin pigmentleri, ışığa duyarlılaştırılmış boyar maddeli güneş gözelerinde boyar madde bileşenleri olarak kullanılmaktadır. Bu kullanımlarda, genel olarak asidik ortamda kaplama yapılmış ve çözelti pH değeri bir parametre olarak kabul edilmemiştir. Flüoresans yayınım şiddetinin azalmasının daha etkin bir yük transfer kompleksinin oluşumunun göstergesi olarak kabul edildiği bu çalışmalarda, antosiyanin moleküllerinin bir formunun baskın olarak TiO2 yüzeyine kaplandığı ve bu formun yük transferinden sorumlu olduğu iddia edilmiştir.Bu çalışmada; kaplanma ortamının pH değerinin antosiyanin moleküllerinin yapısal dönüş

pH-dependent coloring of combination effect pigments with anthocyanins from Brassica oleracea var. capitata F. rubra

Mica-titania pearlescent pigments (MTs) were previously coated with organic molecules to obtain combination pigments (CPs) for achieving certain improvements or functionalities. Anthocyanins (ACNs) are molecules that can be extracted from natural resources and exhibit color changes via pH modifications of the enclosing medium. The purpose of the study was to produce a new series of CPs by depositing ACNs on MTs at different pH values, to observe the changes in color, and to associate these changes to thermogravimetrically determined deposition efficiencies in light of spectral differences. The extraction and deposition methods were based on aqueous chemistry and were straightforward. The ACN deposition generally increased with increasing pH and correlated with the consistency between the charges of the MT surfaces and the dominant ACN species at a specific pH value. The fluorescence of the CPs was inversely correlated with the deposition quantities invoking the possibility of a quenching effect

Structures of multisubunit membrane complexes with the CRYO ARM 200

Progress in structural membrane biology has been significantly accelerated by the ongoing 'Resolution Revolution' in cryo electron microscopy (cryo-EM). In particular, structure determination by single particle analysis has evolved into the most powerful method for atomic model building of multisubunit membrane protein complexes. This has created an ever increasing demand in cryo-EM machine time, which to satisfy is in need of new and affordable cryo electron microscopes. Here, we review our experience in using the JEOL CRYO ARM 200 prototype for the structure determination by single particle analysis of three different multisubunit membrane complexes: the Thermus thermophilus V-type ATPase VO complex, the Thermosynechococcus elongatus photosystem I monomer and the flagellar motor LP-ring from Salmonella enterica