Proteins
adopt different higher-order structures (HOS) to enable
their unique biological functions. Understanding the complexities
of protein higher-order structures and dynamics requires integrated
approaches, where mass spectrometry (MS) is now positioned to play
a key role. One of those approaches is protein footprinting. Although
the initial demonstration of footprinting was for the HOS determination
of protein/nucleic acid binding, the concept was later adapted to
MS-based protein HOS analysis, through which different covalent labeling
approaches “mark” the solvent accessible surface area
(SASA) of proteins to reflect protein HOS. Hydrogen–deuterium
exchange (HDX), where deuterium in D2O replaces hydrogen
of the backbone amides, is the most common example of footprinting.
Its advantage is that the footprint reflects SASA and hydrogen bonding,
whereas one drawback is the labeling is reversible. Another example
of footprinting is slow irreversible labeling of functional groups
on amino acid side chains by targeted reagents with high specificity,
probing structural changes at selected sites. A third footprinting
approach is by reactions with fast, irreversible labeling species
that are highly reactive and footprint broadly several amino acid
residue side chains on the time scale of submilliseconds. All of these
covalent labeling approaches combine to constitute a problem-solving
toolbox that enables mass spectrometry as a valuable tool for HOS
elucidation. As there has been a growing need for MS-based protein
footprinting in both academia and industry owing to its high throughput
capability, prompt availability, and high spatial resolution, we present
a summary of the history, descriptions, principles, mechanisms, and
applications of these covalent labeling approaches. Moreover, their
applications are highlighted according to the biological questions
they can answer. This review is intended as a tutorial for MS-based
protein HOS elucidation and as a reference for investigators seeking
a MS-based tool to address structural questions in protein science.
Soil sickness is a critical problem for eggplant (Solanum melongena L.) under continuous cropping that affects sustainable eggplant production. Relay intercropping is a significant technique on promoting soil quality, improving eco-environment, and raising output. Field experiments were conducted from September 2010 to November 2012 in northwest China to determine the effects of relay intercropping eggplant with garlic (Allium sativum L.) on soil enzyme activities, available nutrient contents, and pH value under a plastic tunnel. Three treatments were in triplicate using randomized block design: eggplant monoculture (CK), eggplant relay intercropping with normal garlic (NG) and eggplant relay intercropping with green garlic (GG). The major results are as follows: (1) the activities of soil invertase, urease, and alkaline phosphatase were generally enhanced in NG and GG treatments; (2) relay intercropping significantly increased the soil available nutrient contents, and they were mostly higher in GG than NG. On April 11, 2011, the eggplant/garlic co-growth stage, the available nitrogen content in GG was 76.30 mg·kg−1, significantly higher than 61.95 mg·kg−1 in NG. For available potassium on April 17, 2012, they were 398.48 and 387.97 mg·kg−1 in NG and GG, both were significantly higher than 314.84 mg·kg−1 in CK; (3) the soil pH showed a significantly higher level in NG treatment, but lower in GG treatment compared with CK. For the last samples in 2012, soil pH in NG and GG were 7.70 and 7.46, the highest and lowest one among them; (4) the alkaline phosphatase activity and pH displayed a similar decreasing trend with continuous cropping. These findings indicate that relay intercropping eggplant with garlic could be an ideal farming system to effectively improve soil nutrient content, increase soil fertility, and alleviate soil sickness to some extent. These findings are important in helping to develop sustainable eggplant production.
The edge sites of MoS2 are catalytically active for hydrogen evolution reactions (HER). However, pristine edge sites usually contain only intrinsic atoms or defects, limiting the tuning of on‐site hydrogen species adsorption and desorption, the critical steps for HER. In addition, the number of atoms on pristine edges is small compared to that of electrochemically inert atoms in bulk. Thus, it is desirable to develop a scalable technique of creating a large number of highly HER‐active edge sites. Here, a plasma etching strategy is developed for creating MoS2 edge electrodes with a controllable number of active sites that enable the quantitative characterization of their HER activity using a local probe method. Fluorine atoms with large electronegativity are doped on the MoS2 edge sites that lead to a fivefold activity enhancement compared to that from pristine edges and is attributed to the more moderate binding energy for hydrogen species. The scalability of such a method is further demonstrated by activating MoS2 catalyst in macroscopic quantities with enhanced HER performance and stability. The work provides two‐dimensional materials as a platform for understanding the doping effect on the edge sites at atomic‐level, and offers a novel route for the design of efficient catalysts.
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