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Lytic polysaccharide monooxygenases (LPMOs) have a unique ability to activate molecular oxygen for subsequent oxidative cleavage of glycosidic bonds. To provide insight into the mode of action of these industrially important enzymes, we have performed an integrated NMR/electron paramagnetic resonance (EPR) study into the detailed aspects of an AA10 LPMO–substrate interaction. Using NMR spectroscopy, we have elucidated the solution-phase structure of apo-BlLPMO10A from Bacillus licheniformis, along with solution-phase structural characterization of the Cu(I)-LPMO, showing that the presence of the metal has minimal effects on the overall protein structure. We have, moreover, used paramagnetic relaxation enhancement (PRE) to characterize Cu(II)-LPMO by NMR spectroscopy. In addition, a multifrequency continuous-wave (CW)-EPR and 15N-HYSCORE spectroscopy study on the uniformly isotope-labeled 63Cu(II)-bound 15N-BlLPMO10A along with its natural abundance isotopologue determined copper spin-Hamiltonian parameters for LPMOs to markedly improved accuracy. The data demonstrate that large changes in the Cu(II) spin-Hamiltonian parameters are induced upon binding of the substrate. These changes arise from a rearrangement of the copper coordination sphere from a five-coordinate distorted square pyramid to one which is four-coordinate near-square planar. There is also a small reduction in metal–ligand covalency and an attendant increase in the d(x²−y²) character/energy of the singly occupied molecular orbital (SOMO), which we propose from density functional theory (DFT) calculations predisposes the copper active site for the formation of a stable Cu–O2 intermediate. This switch in orbital character upon addition of chitin provides a basis for understanding the coupling of substrate binding with O2 activation in chitin-active AA10 LPMOs. [ABSTRACT FROM AUTHOR]

Key points: Mutations in the calmodulin protein (CaM) are associated with arrhythmia syndromes.This study focuses on understanding the structural characteristics of CaM disease mutants and their interactions with the voltage‐gated calcium channel CaV1.2.Arrhythmia mutations in CaM can lead to loss of Ca2+ binding, uncoupling of Ca2+ binding cooperativity, misfolding of the EF‐hands and altered affinity for the calcium channel.These results help us to understand how different CaM mutants have distinct effects on structure and interactions with protein targets to cause disease. Calmodulinopathies are life‐threatening arrhythmia syndromes that arise from mutations in calmodulin (CaM), a calcium sensing protein whose sequence is completely conserved across all vertebrates. These mutations have been shown to interfere with the function of cardiac ion channels, including the voltage‐gated Ca2+ channel CaV1.2 and the ryanodine receptor (RyR2), in a mutation‐specific manner. The ability of different CaM disease mutations to discriminate between these channels has been enigmatic. We present crystal structures of several C‐terminal lobe mutants and an N‐terminal lobe mutant in complex with the CaV1.2 IQ domain, in conjunction with binding assays and complementary structural biology techniques. One mutation (D130G) causes a pathological conformation, with complete separation of EF‐hands within the C‐lobe and loss of Ca2+ binding in EF‐hand 4. Another variant (Q136P) has severely reduced affinity for the IQ domain, and shows changes in the CD spectra under Ca2+‐saturating conditions when unbound to the IQ domain. Ca2+ binding to a pair of EF‐hands normally proceeds with very high cooperativity, but we found that N98S CaM can adopt different conformations with either one or two Ca2+ ions bound to the C‐lobe, possibly disrupting the cooperativity. An N‐lobe variant (N54I), which causes severe stress‐induced arrhythmia, does not show any major changes in complex with the IQ domain, providing a structural basis for why this mutant does not affect function of CaV1.2. These findings show that different CaM mutants have distinct effects on both the CaM structure and interactions with protein targets, and act via distinct pathological mechanisms to cause disease. Key points: Mutations in the calmodulin protein (CaM) are associated with arrhythmia syndromes.This study focuses on understanding the structural characteristics of CaM disease mutants and their interactions with the voltage‐gated calcium channel CaV1.2.Arrhythmia mutations in CaM can lead to loss of Ca2+ binding, uncoupling of Ca2+ binding cooperativity, misfolding of the EF‐hands and altered affinity for the calcium channel.These results help us to understand how different CaM mutants have distinct effects on structure and interactions with protein targets to cause disease. [ABSTRACT FROM AUTHOR]

Background: In our metabolomics studies we have noticed that repeated NMR acquisition on the same sample can result in altered metabolite signal intensities. Aims: To investigate the reproducibility of repeated NMR acquisition on selected metabolites in serum and plasma from two large human metabolomics studies. Methods: Two peak regions for each metabolite were integrated and changes occurring after reacquisition were correlated. Results: Integral changes were generally small, but serum citrate signals decreased significantly in some samples. Conclusions: Several metabolite integrals were not reproducible in some of the repeated spectra. Following established protocols, randomising analysis order and biomarker validation are important. [ABSTRACT FROM AUTHOR]

A study of the interaction between the Fusarium solani pisi cutinase mutant S120A and spin-labeled 4,4-dimethyloxazoline-N-oxyl-(DOXYL)-stearoyl-glycerol substrates in micellar system is conducted. Relaxation enhancements indicative of spatial proximity between the DOXYL group in the lipid chain and some hydrophobic residues surrounding the active site could be found.

A study of lipolytic activity of lipases from Fusarium solani pisi, Rhizomucor miehei, Pseudomonas cepacia, and Humicola lanuginosa is presented. Their activities toward triolein provide clear evidence for considerable enzymatic activity under acidic conditions.