Structure of a bacterial adhesin reveals its role in forming a mixed-species symbiotic community with diatoms on sea ice.

We study the properties of water at the surface of an antifreeze protein with femtosecond surface sum frequency generation spectroscopy. We find clear evidence for the presence of ice-like water layers at the ice-binding site of the protein in aqueous solution at temperatures above the freezing point. Decreasing the temperature to the biological working temperature of the protein (0°C to −2°C) increases the amount of ice-like water, while a single point mutation in the ice-binding site is observed to completely disrupt the ice-like character and to eliminate antifreeze activity. Our observations indicate that not the protein itself but ordered ice-like water layers are responsible for the recognition and binding to ice.antifreeze proteins | sum frequency generation | protein hydration

Antibody-based molecular recognition plays a dominant role in the life sciences ranging from applications in diagnostics and molecular imaging to targeted drug delivery and therapy. Here we report a generic approach to introduce protease sensitivity into antibody-based targeting by taking advantage of the intrinsic ability of antibodies to engage in multivalent interactions. Bivalent peptide ligands with dsDNA as a rigid linker were shown to effectively bridge the relatively large distance between the two antigen binding sites within the same antibody, yielding exclusively the cyclic 1 : 1 antibody-ligand complex. Size exclusion chromatography and small angle X-scattering were used to study the types of complexes formed between a model antibody and peptide-dsDNA conjugates displaying 1 or 2 peptide ligands and different linker lengths. Competitive binding assays using fluorescence anisotropy revealed that the interaction between bivalent peptide-dsDNA conjugate and antibody is 500-fold stronger than that of the monovalent peptide, allowing effective blocking of the antigen binding sites in a non-covalent manner. Cleavage of the linker between the peptide epitope and the DNA by matrix metalloprotease 2 disables this strong bivalent interaction and was shown to effectively restore the binding activity of the antibody in an in vitro binding assay. The approach presented here is broadly applicable, because it takes advantage of the Y-shaped multivalent presentation of antigen binding sites common to all antibodies and could be extended to control antibody activity by other input signals.

Poly(vinyl alcohol) (PVA) is a water‐soluble synthetic polymer well‐known to effectively block the recrystallization of ice. The effect of polymer chain architecture on the ice recrystallization inhibition (IRI) by PVA remains unexplored. In this work, the synthesis of PVA molecular bottlebrushes is described via a combination of atom‐transfer radical polymerization and reversible addition‐fragmentation chain‐transfer polymerization. The facile preparation of the PVA bottlebrushes is performed via the selective hydrolysis of the chloroacetate esters of the poly(vinyl chloroacetate) (PVClAc) side chains of a PVClAc precursor bottlebrush. The IRI efficacy of the PVA bottlebrush is quantitatively compared to linear PVA. The results show that even if the PVA chains are densely grafted onto a rigid polymer backbone, the IRI activity of PVA is maintained, demonstrating the flexibility in PVA polymer chain architecture for the design of synthetic PVA‐based ice growth inhibitors.

Articles you may be interested inExplicit-water theory for the salt-specific effects and Hofmeister series in protein solutions J. Chem. Phys. 144, 215101 (2016) Ice binding proteins (IBPs) are produced by various cold-adapted organisms to protect their body tissues against freeze damage. First discovered in Antarctic fish living in shallow waters, IBPs were later found in insects, microorganisms, and plants. Despite great structural diversity, all IBPs adhere to growing ice crystals, which is essential for their extensive repertoire of biological functions. Some IBPs maintain liquid inclusions within ice or inhibit recrystallization of ice, while other types suppress freezing by blocking further ice growth. In contrast, ice nucleating proteins stimulate ice nucleation just below 0 C. Despite huge commercial interest and major scientific breakthroughs, the precise working mechanism of IBPs has not yet been unraveled. In this review, the authors outline the state-of-the-art in experimental and theoretical IBP research and discuss future scientific challenges. The interaction of IBPs with ice, water and ions is examined, focusing in particular on ice growth inhibition mechanisms.