Molecular basis for different substrate-binding sites and chaperone functions of the BRICHOS domain.

Proteins can misfold into fibrillar or amorphous aggregates and molecular chaperones act as crucial guardians against these undesirable processes. The BRICHOS chaperone domain, found in several otherwise unrelated proproteins that contain amyloidogenic regions, effectively inhibits amyloid formation and toxicity but can in some cases also prevent non-fibrillar, amorphous protein aggregation. Here, we elucidate the molecular basis behind the multifaceted chaperone activities of the BRICHOS domain from the Bri2 proprotein. High-confidence AlphaFold2 and RoseTTAFold predictions suggest that the intramolecular amyloidogenic region (Bri23) is part of the hydrophobic core of the proprotein, where it occupies the proposed amyloid binding site, explaining the markedly reduced ability of the proprotein to prevent an exogenous amyloidogenic peptide from aggregating. However, the BRICHOS-Bri23 complex maintains its ability to form large polydisperse oligomers that prevent amorphous protein aggregation. A cryo-EM-derived model of the Bri2 BRICHOS oligomer is compatible with surface-exposed hydrophobic motifs that get exposed and come together during oligomerization, explaining its effects against amorphous aggregation. These findings provide a molecular basis for the BRICHOS chaperone domain function, where distinct surfaces are employed against different forms of protein aggregation.

A home-based pulmonary rehabilitation mHealth system to enhance the exercise capacity of patients with COPD: development and evaluation.

BACKGROUND: Patients with chronic obstructive pulmonary disease (COPD) experience deficits in exercise capacity and physical activity as their disease progresses. Pulmonary rehabilitation (PR) can enhance exercise capacity of patients and it is crucial for patients to maintain a lifestyle which is long-term physically active. This study aimed to develop a home-based rehabilitation mHealth system incorporating behavior change techniques (BCTs) for COPD patients, and evaluate its technology acceptance and feasibility. METHODS: Guided by the medical research council (MRC) framework the process of this study was divided into four steps. In the first step, the prescription was constructed. The second step was to formulate specific intervention functions based on the behavior change wheel theory. Subsequently, in the third step we conducted iterative system development. And in the last step two pilot studies were performed, the first was for the improvement of system functions and the second was to explore potential clinical benefits and validate the acceptance and usability of the system. RESULTS: A total of 17 participants were enrolled, among them 12 COPD participants completed the 12-week study. For the clinical outcomes, Six-Minute Walk Test (6MWT) showed significant difference (P = .023) over time with an improvement exceeded the minimal clinically important difference (MCID). Change in respiratory symptom (CAT score) was statistically different (P = .031) with a greater decrease of - 3. The mMRC levels reduced overall and showed significant difference. The overall compliance of this study reached 82.20% (± 1.68%). The results of questionnaire and interviews indicated good technology acceptance and functional usability. The participants were satisfied with the mHealth-based intervention. CONCLUSIONS: This study developed a home-based PR mHealth system for COPD patients. We showed that the home-based PR mHealth system incorporating BCTs is a feasible and acceptable intervention for COPD patients, and COPD patients can benefit from the intervention delivered by the system. The proposed system played an important auxiliary role in offering exercise prescription according to the characteristics of patients. It provided means and tools for further individuation of exercise prescription in the future.

MrpH, a new class of metal-binding adhesin, requires zinc to mediate biofilm formation.

Proteus mirabilis, a Gram-negative uropathogen, is a major causative agent in catheter-associated urinary tract infections (CAUTI). Mannose-resistant Proteus-like fimbriae (MR/P) are crucially important for P. mirabilis infectivity and are required for biofilm formation and auto-aggregation, as well as for bladder and kidney colonization. Here, the X-ray crystal structure of the MR/P tip adhesin, MrpH, is reported. The structure has a fold not previously described and contains a transition metal center with Zn2+ coordinated by three conserved histidine residues and a ligand. Using biofilm assays, chelation, metal complementation, and site-directed mutagenesis of the three histidines, we show that an intact metal binding site occupied by zinc is essential for MR/P fimbria-mediated biofilm formation, and furthermore, that P. mirabilis biofilm formation is reversible in a zinc-dependent manner. Zinc is also required for MR/P-dependent agglutination of erythrocytes, and mutation of the metal binding site renders P. mirabilis unfit in a mouse model of UTI. The studies presented here provide important clues as to the mechanism of MR/P-mediated biofilm formation and serve as a starting point for identifying the physiological MR/P fimbrial receptor.

Structure of the N-terminal domain of Euprosthenops australis dragline silk suggests that conversion of spidroin dope to spider silk involves a conserved asymmetric dimer intermediate.

Spider silk is a biomaterial with exceptional mechanical toughness, and there is great interest in developing biomimetic methods to produce engineered spider silk-based materials. However, the mechanisms that regulate the conversion of spider silk proteins (spidroins) from highly soluble dope into silk are not completely understood. The N-terminal domain (NT) of Euprosthenops australis dragline silk protein undergoes conformational and quaternary-structure changes from a monomer at a pH above 7 to a homodimer at lower pH values. Conversion from the monomer to the dimer requires the protonation of three conserved glutamic acid residues, resulting in a low-pH `locked' dimer stabilized by symmetric electrostatic interactions at the poles of the dimer. The detailed molecular events during this transition are still unresolved. Here, a 2.1 Šresolution crystal structure of an NT T61A mutant in an alternative, asymmetric, dimer form in which the electrostatic interactions at one of the poles are dramatically different from those in symmetrical dimers is presented. A similar asymmetric dimer structure from dragline silk of Nephila clavipes has previously been described. It is suggested that asymmetric dimers represent a conserved intermediate state in spider silk formation, and a revised `lock-and-trigger' mechanism for spider silk formation is presented.

Structures of two fimbrial adhesins, AtfE and UcaD, from the uropathogen Proteus mirabilis.

The important uropathogen Proteus mirabilis encodes a record number of chaperone/usher-pathway adhesive fimbriae. Such fimbriae, which are used for adhesion to cell surfaces/tissues and for biofilm formation, are typically important virulence factors in bacterial pathogenesis. Here, the structures of the receptor-binding domains of the tip-located two-domain adhesins UcaD (1.5 Šresolution) and AtfE (1.58 Šresolution) from two P. mirabilis fimbriae (UCA/NAF and ATF) are presented. The structures of UcaD and AtfE are both similar to the F17G type of tip-located fimbrial receptor-binding domains, and the structures are very similar despite having only limited sequence similarity. These structures represent an important step towards a molecular-level understanding of P. mirabilis fimbrial adhesins and their roles in the complex pathogenesis of urinary-tract infections.

Molecular and Biochemical Analysis of Chalcone Synthase from Freesia hybrid in flavonoid biosynthetic pathway.

Chalcone synthase (CHS) catalyzes the first committed step in the flavonoid biosynthetic pathway. In this study, the cDNA (FhCHS1) encoding CHS from Freesia hybrida was successfully isolated and analyzed. Multiple sequence alignments showed that both the conserved CHS active site residues and CHS signature sequence were found in the deduced amino acid sequence of FhCHS1. Meanwhile, crystallographic analysis revealed that protein structure of FhCHS1 is highly similar to that of alfalfa CHS2, and the biochemical analysis results indicated that it has an enzymatic role in naringenin biosynthesis. Moreover, quantitative real-time PCR was performed to detect the transcript levels of FhCHS1 in flowers and different tissues, and patterns of FhCHS1 expression in flowers showed significant correlation to the accumulation patterns of anthocyanin during flower development. To further characterize the functionality of FhCHS1, its ectopic expression in Arabidopsis thaliana tt4 mutants and Petunia hybrida was performed. The results showed that overexpression of FhCHS1 in tt4 mutants fully restored the pigmentation phenotype of the seed coats, cotyledons and hypocotyls, while transgenic petunia expressing FhCHS1 showed flower color alteration from white to pink. In summary, these results suggest that FhCHS1 plays an essential role in the biosynthesis of flavonoid in Freesia hybrida and may be used to modify the components of flavonoids in other plants.

The Escherichia coli CysZ is a pH dependent sulfate transporter that can be inhibited by sulfite.

The Escherichia coli inner membrane protein CysZ mediates the sulfate uptake subsequently utilized for the synthesis of sulfur-containing compounds in cells. Here we report the purification and functional characterization of CysZ. Using Isothermal Titration Calorimetry, we have observed interactions between CysZ and its putative substrate sulfate. Additional sulfur-containing compounds from the cysteine synthesis pathway have also been analyzed for their abilities to interact with CysZ. Our results suggest that CysZ is dedicated to a specific pathway that assimilates sulfate for the synthesis of cysteine. Sulfate uptake via CysZ into E. coli whole cells and proteoliposome offers direct evidence of CysZ being able to mediate sulfate uptake. In addition, the cysteine synthesis pathway intermediate sulfite can interact directly with CysZ with higher affinity than sulfate. The sulfate transport activity is inhibited in the presence of sulfite, suggesting the existence of a feedback inhibition mechanism in which sulfite regulates sulfate uptake by CysZ. Sulfate uptake assays performed at different extracellular pH and in the presence of a proton uncoupler indicate that this uptake is driven by the proton gradient.