S-adenosylmethionine (SAM) is one of the most important enzyme substrates. It is vital for the function of various proteins, including large group of methyltransferases (MTs). Intriguingly, some bacterial and eukaryotic MTs, while catalysing the same reaction, possess significantly different topologies, with the former being a knotted one. Here, we conducted a comprehensive analysis of SAM conformational space and factors that affect its vastness. We investigated SAM in two forms: free in water (via NMR studies and explicit solvent simulations) and bound to proteins (based on all data available in the PDB and on all-atom molecular dynamics simulations in water). We identified structural descriptors-angles which show the major differences in SAM conformation between unknotted and knotted methyltransferases. Moreover, we report that this is caused mainly by a characteristic for knotted MTs compact binding site formed by the knot and the presence of adenine-binding loop. Additionally, we elucidate conformational restrictions imposed on SAM molecules by other protein groups in comparison to conformational space in water.
Nuclear magnetic resonance spectroscopy (NMR) is a versatile tool of chemical analysis allowing one to determine structures of molecules with atomic resolution. Particularly informative are two-dimensional (2D) experiments that directly identify atoms coupled by chemical bonds or a through-space interaction. Thus, NMR could potentially be powerful tool to study reactions in situ and explain their mechanisms. Unfortunately, 2D NMR is very time-consuming and thus often cannot serve as a "snapshot" technique for in situ reaction monitoring. Particularly difficult is the case of spectra, in which resonance frequencies vary in the course of reaction. This leads to resolution and sensitivity loss, often hindering the detection of transient products. In this paper we introduce a novel approach to correct such nonstationary 2D NMR signals and raise the detection limits over 10 times. We demonstrate success of its application for studying the mechanism of the reaction of AgSO 4 -induced synthesis of diphenylmethane-type compounds. Several reactions occur in the studied mixture of benzene and toluene, all with rather low yield and leading to compounds with similar chemical shifts. Nevertheless, with the use of a proposed 2D NMR approach we were able to describe complex mechanisms of diphenylmethane formation involving AgSO 4 -induced toluene deprotonation and formation of benzyl carbocation, followed by nucleophilic attacks.
Development of robust
and cost-effective smart materials requires
rational chemical nanoengineering to provide viable technological
solutions for a wide range of applications. Recently, a powerful approach
based on the electrografting of diazonium salts has attracted a great
deal of attention due to its numerous technological advantages. Several
studies on graphene-based materials reveal that the covalent attachment
of aryl groups via the above approach could lead to additional beneficial
properties of this versatile material. Here, we developed the covalently
linked metalorganic wires on two transparent, cheap, and conductive
materials: fluorine-doped tin oxide (FTO) and FTO/single-layer graphene
(FTO/SLG). The wires are terminated with nitrilotriacetic acid metal
complexes, which are universal molecular anchors to immobilize His6-tagged proteins, such as biophotocatalysts and other types
of redox-active proteins of great interest in biotechnology, optoelectronics,
and artificial photosynthesis. We show for the first time that the
covalent grafting of a diazonium salt precursor on two different electron-rich
surfaces leads to the formation of the molecular wires that promote
p-doping of SLG concomitantly with a significantly enhanced unidirectional
cathodic photocurrent up to 1 μA cm–2. Density
functional theory modeling reveals that the exceptionally high photocurrent
values are due to two distinct mechanisms of electron transfer originating
from different orbitals/bands of the diazonium-derived wires depending
on the nature of the chelating metal redox center. Importantly, the
novel metalorganic interfaces reported here exhibit minimized back
electron transfer, which is essential for the maximization of solar
conversion efficiency.
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