The effect of linker conformation on performance and stability of a two-domain lytic polysaccharide monooxygenase

A considerable number of lytic polysaccharide monooxygenases (LPMOs) and other carbohydrate-active enzymes are modular, with catalytic domains being tethered to additional domains, such as carbohydrate-binding modules, by flexible linkers. While such linkers may affect the structure, function, and stability of the enzyme, their roles remain largely enigmatic, as do the reasons for natural variation in length and sequence. Here, we have explored linker functionality using the two-domain cellulose-active ScLPMO10C from Streptomyces coelicolor as a model system. In addition to investigating the WT enzyme, we engineered three linker variants to address the impact of both length and sequence and characterized these using small-angle X-ray scattering, NMR, molecular dynamics simulations, and functional assays. The resulting data revealed that, in the case of ScLPMO10C, linker length is the main determinant of linker conformation and enzyme performance. Both the WT and a serine-rich variant, which have the same linker length, demonstrated better performance compared with those with either a shorter linker or a longer linker. A highlight of our findings was the substantial thermostability observed in the serine-rich variant. Importantly, the linker affects thermal unfolding behavior and enzyme stability. In particular, unfolding studies show that the two domains unfold independently when mixed, whereas the full-length enzyme shows one cooperative unfolding transition, meaning that the impact of linkers in biomass-processing enzymes is more complex than mere structural tethering.

Three-Component Self-Assembly Changes its Course: A Leap from Simple Polymers to 3D Networks of Spherical Host-Guest Assemblies

One‐pot self‐assembly reactions of the polyphosphorus complex [Cp*Fe(η⁵‐P₅)] (A), a coinage metal salt AgSbF₆, and flexible aliphatic dinitriles NC(CH₂)_xCN (x=1–10) yield 1D, 2D, and 3D coordination polymers. The seven‐membered backbone of the dinitrile was experimentally found as the borderline for the self‐assembly system furnishing products of different kinds. At x<7, various rather simple polymers are exclusively formed possessing either 0D or 1D Ag/A structural motifs connected by dinitrile spacers, while at x≥7, the self‐assembly switches to unprecedented extraordinary 3D networks of nano‐sized host–guest assemblies (SbF₆)@[(A)₉Ag₁₁]¹¹⁺ (x=7) or (A)@[(A)₁₂Ag₁₂]¹²⁺ (x=8–10) linked by dinitriles. The polycationic nodes represent the first superspheres based on A and silver and are host–guest able. All products are characterized by NMR spectroscopy, mass spectrometry, and single‐crystal X‐ray diffraction. The assemblies [(A)₁₂Ag₁₂]¹²⁺ were visualized by transmission electron microscopy.

Discovery of Diphenoxy Derivatives with Flexible Linkers as Ligands for β-Amyloid Plaques

The highly rigid and planar scaffolds with π-conjugated systems have been widely considered to be indispensable for β-amyloid (Aβ) binding ligands. In this study, a library of diphenoxy compounds with different types of more flexible linkers as Aβ ligands were synthesized and evaluated. Most of them displayed good affinity (K_i < 100 nM) for Aβ_1-42 aggregates, and some ligands even showed values of K_i less than 10 nM. Structure-activity relationship analysis revealed that modification on the linkers or substituents tolerated great flexibility, which challenged the long-held belief that rigid and planar structures are exclusively favored for Aβ binding. Three ligands were labeled by iodine-125, and they exhibited good properties in vitro and in vivo, which further supported that this flexible scaffold was potential and promising for the development of Aβ imaging agents.