Structural and functional analyses of photosystem II in the marine diatom Phaeodactylum tricornutum.

A descendant of the red algal lineage, diatoms are unicellular eukaryotic algae characterized by thylakoid membranes that lack the spatial differentiation of stroma and grana stacks found in green algae and higher plants. While the photophysiology of diatoms has been studied extensively, very little is known about the spatial organization of the multimeric photosynthetic protein complexes within their thylakoid membranes. Here, using cryo-electron tomography, proteomics, and biophysical analyses, we elucidate the macromolecular composition, architecture, and spatial distribution of photosystem II complexes in diatom thylakoid membranes. Structural analyses reveal 2 distinct photosystem II populations: loose clusters of complexes associated with antenna proteins and compact 2D crystalline arrays of dimeric cores. Biophysical measurements reveal only 1 photosystem II functional absorption cross section, suggesting that only the former population is photosynthetically active. The tomographic data indicate that the arrays of photosystem II cores are physically separated from those associated with antenna proteins. We hypothesize that the islands of photosystem cores are repair stations, where photodamaged proteins can be replaced. Our results strongly imply convergent evolution between the red and the green photosynthetic lineages toward spatial segregation of dynamic, functional microdomains of photosystem II supercomplexes.

Point-of-Care Synchronous Virtual Radiology Consultations for Atherosclerotic Disease in Primary Care: A Cluster-Randomized Study.

PURPOSE: Synchronous virtual visits are an emerging model of care, and their feasibility has been demonstrated in radiology. The purpose of this study was to assess the value of point-of-care virtual radiology primary care consultations for atherosclerotic vascular disease management. METHODS: In this institutional review board-approved study, 107 age- and gender-matched patients were assigned to control (n = 62) and intervention (n = 45) arms with the following inclusion criteria: (1) age > 45 years, (2) consult with a primary care physician (PCP), and (3) recent CT of the chest or abdomen demonstrating atherosclerotic calcification. In the intervention arm, virtual real-time radiology consultation with referring PCPs and patients was conducted, with review of CT images focused on the extent of vascular atherosclerosis. Patients in the control arm followed the current standard of care of PCPs' discussing relevant imaging results, if any. RESULTS: Thirty-one patients in the intervention arm and 31 patients in the control arm completed the study (control: 64.5% women; mean age, 68 years; intervention: 67.7% women; mean age, 67 years). Discussion of imaging findings occurred with all patients in the intervention arm (discussion with PCP and virtual consultation with radiologist) and with 45% of patients in the control arm (PCP only; P < .001). All patients in the intervention arm indicated that seeing or discussing their images improved their understanding of their disease, compared with 85% of patients in the control arm (P = .04). In the intervention arm, 10 of 31 patients (32.2%) left the visit with changes in prescriptions for statins or antihypertensive medications, compared with only 4 of 31 patients (13%) in the control arm (P = .04). CONCLUSIONS: Point-of-care radiology virtual visits enhance patient understanding and may influence the longitudinal management of atherosclerotic disease in primary care.