Bioimaging and Biodistribution of the Metal-Ion-Controlled Self-Assembly of PYY3-36 Studied by SPECT/CT.

The controlled self-assembly of peptide- and protein-based pharmaceuticals is of central importance for their mode of action and tuning of their properties. Peptide YY3-36 (PYY3-36 ) is a 36-residue peptide hormone that reduces food intake when peripherally administered. Herein, we describe the synthesis of a PYY3-36 analogue functionalized with a metal-ion-binding 2,2'-bipyridine ligand that enables self-assembly through metal complexation. Upon addition of CuII , the bipyridine-modified PYY3-36 peptide binds stoichiometric quantities of metal ions in solution and contributes to the organization of higher-order assemblies. In this study, we aimed to explore the size effect of the self-assembly in vivo by using non-invasive quantitative single-photon emission computed tomography/computed tomography (SPECT/CT) imaging. For this purpose, bipyridine-modified PYY3-36 was radiolabeled with a chelator holding 111 InIII , followed by the addition of CuII to the bipyridine ligand. SPECT/CT imaging and biodistribution studies showed fast renal clearance and accumulation in the kidney cortex. The radiolabeled bipyridyl-PYY3-36 conjugates with and without CuII presented a slightly slower excretion 1 h post injection compared to the unmodified-PYY3-36 , thus demonstrating that higher self-assemblies of the peptide might have an effect on the pharmacokinetics.

Substrate specificity of novel GH16 endo-ß-(1→3)-galactanases acting on linear and branched ß-(1→3)-galactooligosaccharides.

Arabinogalactan proteins are proteoglycans located in the plant cell wall. Most arabinogalactan proteins are composed of carbohydrate moieties of ß-(1→3)-galactan main chains with ß-(1→6)-galactan side chains terminated by other glycans. In this study, three novel endo-ß-(1→3)-galactanases were identified and the substrate specificity was further studied using well-defined galactan oligomers. Linear and branched ß-(1→3)-linked galactans, which resemble the carbohydrate core of the arabinogalactan protein, were used for the characterization of endo-ß-(1→3)-galactanases. The identified enzymes required at least three consecutive galactose residues for activity. Non-substituted regions were preferred, but substituents in the -2 and +2 and in some cases also -1 and +1 subsites were tolerated to some extent, depending on the branching pattern, however at a significantly lower rate/frequency.