Cryo-EM structure of an extracellular Geobacter OmcE cytochrome filament reveals tetrahaem packing.

Electrically conductive appendages from the anaerobic bacterium Geobacter sulfurreducens were first observed two decades ago, with genetic and biochemical data suggesting that conductive fibres were type IV pili. Recently, an extracellular conductive filament of G. sulfurreducens was found to contain polymerized c-type cytochrome OmcS subunits, not pilin subunits. Here we report that G. sulfurreducens also produces a second, thinner appendage comprised of cytochrome OmcE subunits and solve its structure using cryo-electron microscopy at ~4.3 Å resolution. Although OmcE and OmcS subunits have no overall sequence or structural similarities, upon polymerization both form filaments that share a conserved haem packing arrangement in which haems are coordinated by histidines in adjacent subunits. Unlike OmcS filaments, OmcE filaments are highly glycosylated. In extracellular fractions from G. sulfurreducens, we detected type IV pili comprising PilA-N and -C chains, along with abundant B-DNA. OmcE is the second cytochrome filament to be characterized using structural and biophysical methods. We propose that there is a broad class of conductive bacterial appendages with conserved haem packing (rather than sequence homology) that enable long-distance electron transport to chemicals or other microbial cells.

Study on the effects of arm abduction angle and cushion support during sonographic examination on the stiffness of supraspinatus muscle of sonographers using shear wave elastography.

OBJECTIVES: The incidence of work-related musculoskeletal disorder remains high in sonography. The aims of this study are to determine the changes in muscle stiffness with different arm abduction angles, and to investigate the effect of cushion support on reducing muscle load in the supraspinatus when sonographers scan with the arm abducted to different angles. METHODS: This is a prospective crossover study. Twenty-three healthy female subjects aged between 20 and 23 years were included. Subjects were instructed to simulate performing standardized abdominal ultrasound scans. The changes in muscle stiffness of supraspinatus, measured as shear modulus, at rest and at 30°, 45°, and 60° arm abduction angles with and without cushion support were evaluated using shear-wave elastography. Styrofoam support was used for the cushion support. RESULTS: Mean shear moduli of supraspinatus were 27.77 ± 5.84 kPa at rest and 41.63 ± 7.09 kPa, 63.88 ± 14.43 kPa, and 89.76 ± 16.55 kPa for 30°, 45°, and 60° arm abduction respectively, which corresponds to 53%, 116% increase in muscle stiffness when scanning arm abducted from 30° to 45° and 60° (p < .001). After applying cushion support, shear moduli dropped to 24.04 ± 5.60 kPa, 31.98 ± 6.06 kPa, 37.47 ± 5.61 kPa for arm abducted to 30°, 45°, and 60° respectively (p < .001). The muscle stiffnesses between 30° abduction without support and 60° abduction with support had no significant difference (p > .05). CONCLUSIONS: Muscle stiffness of supraspinatus increased with increasing arm abduction angle during ultrasound scanning. Utilizing cushion support underneath the arm was effective in reducing muscle stiffness in supraspinatus. Our results provide scientific justification on postural modifications for sonographers.

Evaluating the Impact of Goal Setting on Improving Diet Quality in Chronic Kidney Disease.

Background: Improving diet quality in chronic kidney disease (CKD) is challenging due to a myriad of competing recommendations. Patient-centered goal setting can facilitate dietary behavior change; however, its role in improving diet quality in CKD has not been investigated. Aim: The aim of the study is to evaluate the effects of goal setting on improving diet quality in stages 3-4 CKD. Methods: Forty-one participants completed a 6-month dietitian-led telehealth (combined coaching calls and text messages) intervention as part of a larger RCT. Participants set one to two diet-related SMART goals and received weekly goal tracking text messages. Dietary intake was assessed using the Australian Eating Survey at baseline, 3, and 6 months, with diet quality determined using the Alternate Healthy Eating Index (AHEI). Results: Significant improvements in AHEI (+6.9 points; 95% CI 1.2-12.7), vegetable (+1.1 serves; 95% CI 0.0-2.3) and fiber intake (+4.2 g; 95% CI 0.2-8.2) were observed at 3 months in participants setting a fruit and/or vegetable goal, compared with those who did not. However, no significant or meaningful changes were observed at 6 months. No other goal setting strategy appeared in effect on diet intake behavior or clinical outcomes in this group of CKD participants. Conclusions: Patient-centered goal setting, particularly in relation to fruit and vegetable intake, as part of a telehealth coaching program, significantly improved diet quality (AHEI), vegetable and fiber intake over 3 months. More support may be required to achieve longer-term behavior change in stages 3-4 CKD patients.

Cell-free production of integral membrane aspartic acid proteases reveals zinc-dependent methyltransferase activity of the Pseudomonas aeruginosa prepilin peptidase PilD.

Integral membrane aspartic acid proteases are receiving growing recognition for their fundamental roles in cellular physiology of eukaryotes and prokaryotes, and may be medically important pharmaceutical targets. The Gram-negative Pseudomonas aeruginosa PilD and the archaeal Methanococcus voltae FlaK were synthesized in the presence of unilamellar liposomes in a cell-free translation system. Cosynthesis of PilD with its full-length substrate, PilA, or of FlaK with its full-length substrate, FlaB2, led to complete cleavage of the substrate signal peptides. Scaled-up synthesis of PilD, followed by solubilization in dodecyl-ß-d-maltoside and chromatography, led to a pure enzyme that retained both of its known biochemical activities: cleavage of the PilA signal peptide and S-adenosyl methionine-dependent methylation of the mature pilin. X-ray fluorescence scans show for the first time that PilD is a zinc-binding protein. Zinc is required for the N-terminal methylation of the mature pilin, but not for signal peptide cleavage. Taken together, our work identifies the P. aeruginosa prepilin peptidase PilD as a zinc-dependent N-methyltransferase and provides a new platform for large-scale synthesis of PilD and other integral membrane proteases important for basic microbial physiology and virulence.