Based on a comparison of discharges for avoidable hospital conditions (AHCs), we find that Paris provides greater access to primary care than Manhattan. Ageadjusted AHC rates are more than 2.5 times as high in Manhattan as in Paris. In contrast, the difference in rates of hospital discharge for "marker conditions" are only about 20 percent higher in Manhattan. Rates of discharges for AHCs are higher among residents of low-income neighborhoods in both cities, but the disparity among high-and low-income neighborhoods is more than twice as great in Manhattan. Our analysis highlights the consequences of access barriers to care in Manhattan, particularly among vulnerable residents. A n i m m e n s e l i t e r at u r e c o m pa r e s national health care systems and attempts to assess their performance and derive "lessons" from countries' experiences.1 Although there are major differences between countries, the focus on national aggregates masks important variations within countries.2 In contrast, the World Cities Project examines cities that share characteristics and problems; this approach provides notable advantages for more refined comparisons and cross-national learning. 3Here we analyze avoidable hospital conditions (AHCs), an indicator of access to primary health care, in Manhattan and Paris, cities that are more alike than their respective countries are (Exhibit 1). The selection of AHCs is only one dimension of health system performance. But in thinking about how health systems can assure access through a combination of health insurance coverage and the 5 1 0 M a r c h /A p r i l 2 0 0 6 D a t a W a t c h

PsbQ is a luminal extrinsic protein component that regulates the water splitting activity of photosystem II (PSII) in plants, algae, and cyanobacteria. However, PsbQ is not observed in the currently available crystal structures of PSII from thermophilic cyanobacteria. The structural location of PsbQ within the PSII complex has therefore remained unknown. Here, we report chemical cross- D of CP47. We further show that genetic deletion of the psbO gene results in the complete absence of PsbQ in PSII complexes as well as the loss of the dimeric form of PSII. Overall, our data provide a molecular-level description of the enigmatic binding site of PsbQ in PSII in a cyanobacterium. These results also help us understand the sequential incorporation of the PsbQ protein during the PSII assembly process, as well as its stabilizing effect on the oxygen evolution activity of PSII.photosystem II structure | protein cross-linking

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Background:The mechanism for association and dissociation of Psb27 and CP43 is poorly understood. Results: Loop E of CP43 undergoes significant conformational change upon D1 processing. Conclusion: D1 processing initiates the dissociation of Psb27 from CP43. Significance: The structural dynamics of the lumenal domain of CP43 plays a critical role in the assembly of functional Photosystem II centers.

Photosystem II (PSII), a large pigment protein complex, undergoes rapid turnover under natural conditions. During assembly of PSII, oxidative damage to vulnerable assembly intermediate complexes must be prevented. Psb28, the only cytoplasmic extrinsic protein in PSII, protects the RC47 assembly intermediate of PSII and assists its efficient conversion into functional PSII. Its role is particularly important under stress conditions when PSII damage occurs frequently. Psb28 is not found, however, in any PSII crystal structure, and its structural location has remained unknown. In this study, we used chemical cross-linking combined with mass spectrometry to capture the transient interaction of Psb28 with PSII. We detected three cross-links between Psb28 and the α-and β-subunits of cytochrome b 559 , an essential component of the PSII reaction-center complex. These distance restraints enable us to position Psb28 on the cytosolic surface of PSII directly above cytochrome b 559 , in close proximity to the Q B site. Protein-protein docking results also support Psb28 binding in this region. Determination of the Psb28 binding site and other biochemical evidence allow us to propose a mechanism by which Psb28 exerts its protective effect on the RC47 intermediate. This study also shows that isotope-encoded cross-linking with the "mass tags" selection criteria allows confident identification of more cross-linked peptides in PSII than has been previously reported. This approach thus holds promise to identify other transient proteinprotein interactions in membrane protein complexes.is a multisubunit pigment-protein complex embedded in the thylakoid membranes of cyanobacteria, algae, and plants. PSII uses light energy to oxidize water to molecular oxygen, simultaneously reducing plastoquinone. Active PSII consists of ∼20 protein subunits and multiple light-harvesting and redox-active cofactors (1, 2).As a result of demanding electron-transfer chemistry, PSII undergoes frequent oxidative damage, necessitating a complex cycle of repair and reassembly (reviewed in ref.3). The assembly occurs stepwise via multiple transient intermediate complexes that are difficult to study because of their low abundance, relatively short lifetimes, and heterogeneity. Crystal structures of the active complex from thermophilic cyanobacteria are available (1, 4, 5), but they do not capture the transient interactions of the various accessory proteins that regulate the life cycle by binding exclusively to intermediate subcomplexes. Nevertheless, significant progress has been made in characterizing these intermediates through complementary use of genetic modification, biochemical analysis, and mass spectrometry (MS) (3, 6-9). Although crystal structures of assembly intermediate complexes are not available, the binding site of one accessory protein, Psb27, on the luminal surface of PSII has been determined by chemical cross-linking and MS (10, 11). This knowledge complements functional studies of Psb27 and provides mechanistic insight into how Psb27 prote...