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The effects of the helix X domain of the PsaB heterodimeric protein complex in the coordination of the reaction centers (RC) of the P700 chlorophyll a dimer were analyzed in genetically engineered H656 mutants of PsaB. The oxidation midpoint potential of P700/P700 + was increased to 40 microVolts in mutant His-656 PsaB RC proteins. The midpoint potential of P700 photosystem I was affected by hydrogen bond that was formed between the His-656 of PsaB RC protein and the carbonyl group of chlorophyll a in P700.

PsaB and PsaC proteins in the photosystem I reaction center contain conserved amino acids sequences which provide the ligands for coordination of the iron-sulfur cluster, F(sub x). Mutagenesis in the prolines P560 and P564 of PsaB formed mutants whose F(sub x) was unaffected, but the interaction of PsaC and the reaction center core was damaged while mutagenesis in the R566 and D562 residues of PsaB formed mutants whose photosystem I was unstable. In addition, the mutants were incapable of photoautotrophic growth.

Conserved histidine residues in the PsaB protein encoded by a chloroplast gene are crucial for photosystem I reaction center accumulation in thylakoid membranes, as revealed by Chlamydomonas reinhardtii chloroplast transformation and site-directed mutagenesis. The post-translational step in reaction center assembly is influenced by variations in the His residues. Mutations on this residue do not regulate the spectral characteristics of the electron transfer component P700.

Abstract Background Although echocardiography is commonly used to evaluate cardiac function after MI, CMR may provide more accurate functional assessment but has not been adequately compared with echo. The primary study objective was to compare metrics of left ventricular volumes and global and regional function determined by cardiac magnetic resonance (CMR) and echocardiography (echo) in patients (pts) with recent myocardial infarction (MI). Methods To compare CMR with echo, 47 consecutive patients (pts 70% male; mean age = 66 ± 11 years) with MI >6 wks previously and scheduled for imaging evaluation were studied by both echo and CMR within 60 min of each other. Readers were blinded to pt information. Pearson's correlation coefficient, paired t-tests, and chi-square tests were used to compare CMR and echo measures. Further comparisons were made between pts and 30 normal controls for CMR and between pts and published normal ranges for echo. Results Measures of volume and function correlated moderately well between CMR and echo (r = 0.54 to 0.75, all p < 0.001), but large and systematic differences were noted in absolute measurements. Echo underestimated left ventricular (LV) volumes (by 69 ml for end-diastolic, 35 ml for end-systolic volume, both p < 0.001), stroke volume (by 34 ml, p < 0.001), and LV ejection fraction (LVEF) (by 4 percentage point, p = 0.02). CMR was much more sensitive to detection of segmental wall motion abnormalities (p < 0.001). CMR comparisons with normal controls confirmed an increase in LV volumes, a decrease in LVEF, and preservation of stroke volume after MI. Conclusion This intra subject comparison after MI found large, systematic differences between CMR and echo measures of volumes, LVEF, and wall motion abnormality despite moderate inter-modality correlations, with echo underestimating each metric. CMR also provided superior detection and quantification of segmental function after MI. Serial studies of LV function in individual patients should use the same modality.

The direction of electron transfer along A-and/or B-branch, by changing the methionine residue that provides a ligand to the central magnesium of eC-A(sub 3) or eC-B(sub 3) in Chlamydomonas reinhardtii, is studied. The results show that both the A-branch and B-branch of the electron transport chain are active and support the bi-directional electron transfer in Chlamydomonas photosystem I.

Background: With multifaceted imaging capabilities, cardiovascular magnetic resonance (CMR) is playing a progressively increasing role in the management of various cardiac conditions. A global registry that harmonizes data from international centers, with participation policies that aim to be open and inclusive of all CMR programs, can support future evidence-based growth in CMR. Methods: The Global CMR Registry (GCMR) was established in 2013 under the auspices of the Society for Cardiovascular Magnetic Resonance (SCMR). The GCMR team has developed a web-based data infrastructure, data use policy and participation agreement, data-harmonizing methods, and site-training tools based on results from an international survey of CMR programs. Results: At present, 17 CMR programs have established a legal agreement to participate in GCMR, amongst them 10 have contributed CMR data, totaling 62,456 studies. There is currently a predominance of CMR centers with more than 10 years of experience (65%), and the majority are located in the United States (63%). The most common clinical indications for CMR have included assessment of cardiomyopathy (21%), myocardial viability (16%), stress CMR perfusion for chest pain syndromes (16%), and evaluation of etiology of arrhythmias or planning of electrophysiological studies (15%) with assessment of cardiomyopathy representing the most rapidly growing indication in the past decade. Most CMR studies involved the use of gadolinium-based contrast media (95%). Conclusions: We present the goals, mission and vision, infrastructure, preliminary results, and challenges of the GCMR. Trial registration: Identification number on ClinicalTrials.gov: NCT02806193. Registered 17 June 2016. [ABSTRACT FROM AUTHOR]

Abstract: The recent crystal structure of photosystem I (PSI) from Thermosynechococcus elongatus shows two nearly symmetric branches of electron transfer cofactors including the primary electron donor, P700, and a sequence of electron acceptors, A, A0 and A1, bound to the PsaA and PsaB heterodimer. The central magnesium atoms of each of the putative primary electron acceptor chlorophylls, A0, are unusually coordinated by the sulfur atom of methionine 688 of PsaA and 668 of PsaB, respectively. We [Ramesh et al. (2004a) Biochemistry 43:1369–1375] have shown that the replacement of either methionine with histidine in the PSI of the unicellular green alga Chlamydomonas reinhardtii resulted in accumulation of A0 − (in 300-ps time scale), suggesting that both the PsaA and PsaB branches are active. This is in contrast to cyanobacterial PSI where studies with methionine-to-leucine mutants show that electron transfer occurs predominantly along the PsaA branch. In this contribution we report that the change of methionine to either leucine or serine leads to a similar accumulation of A0 − on both the PsaA and the PsaB branch of PSI from C. reinhardtii, as we reported earlier for histidine mutants. More importantly, we further demonstrate that for all the mutants under study, accumulation of A0 − is transient, and that reoxidation of A0 − occurs within 1–2 ns, two orders of magnitude slower than in wild type PSI, most likely via slow electron transfer to A1. This illustrates an indispensable role of methionine as an axial ligand to the primary acceptor A0 in optimizing the rate of charge stabilization in PSI. A simple energetic model for this reaction is proposed. Our findings support the model of equivalent electron transfer along both cofactor branches in Photosystem I. [Copyright &y& Elsevier]

Photosystem I (PSI) is a multisubunit pigment-protein complex that uses light energy to transfer electrons from plastocyanin to ferredoxin. Application of genetic engineering to photosynthetic reaction center proteins has led to a significant advancement in our understanding of primary electron transfer events and the role of the protein environment in modulating these processes. Chlamydomonas reinhardtii provides a system particularly amenable to analyze the structure-function relationship of Photosystem I. C. reinhardtii is also a particularly favorable organism for chloroplast transformation because it contains only a single chloroplast and grows heterotrophically when supplemented with acetate. Chlamydomonas has, therefore, served as a model organism for the development of chloroplast transformation procedures and the study of photosynthetic mutants generated using this method. Exogenous cloned cpDNA can be introduced into the chloroplast by using this biolistic gene gun method. DNA-coated tungsten or gold particles are bombarded onto cells. Upon its entry into chloroplasts, the transforming DNA is released from the particles and integrated into the chloroplast genome through homologous recombination. The most versatile chloroplast selectable marker is aminoglycoside adenyl transferase (aadA), which can be expressed in the chloroplast to confer resistance to spectinomycin or streptomycin. This article describes the procedures for chloroplast transformation.

Photosystem (PS)I is a multi-subunit pigment-protein complex that uses light energy to transfer electrons from plastocyanin to ferredoxin. Application of genetic engineering to photo-synthetic reaction center proteins has led to a significant advancement in our understanding of primary electron transfer events and the role of the protein environment in modulating these processes. Chlamydomonas reinhardtii provides a system particularly amenable to analyze the structure-function relationship of PSI. Chlamydomonas reinhardtii is also a favorable organism for chloroplast transformation because it contains a single chloroplast and grows heterotrophically when supplemented with acetate. Chlamydomonas has served as a model organism for the development of chloroplast transformation procedures and the study of photosynthetic mutants generated using this method. Exogenous cloned cpDNA can be introduced into the chloroplast by using this biolistic gene gun method. DNA-coated tungsten or gold particles are bombarded onto cells. Upon its entry into chloroplasts, the transforming DNA is released from the particles and integrated into the chloroplast genome through homologous recombination. The most versatile chloroplast selectable marker is aminoglycoside adenyl transferase (aadA), which can be expressed in the chloroplast to confer resistance to spectinomycin or streptomycin. This chapter describes the procedures for chloroplast transformation.