Radiation Damage and Racemic Protein Crystallography Reveal the Unique Structure of the GASA/Snakin Protein Superfamily

Proteins from the GASA/snakin superfamily are common in plant proteomes and have diverse functions, including hormonal crosstalk, development, and defense. One 63‐residue member of this family, snakin‐1, an antimicrobial protein from potatoes, has previously been chemically synthesized in a fully active form. Herein the 1.5 Å structure of snakin‐1, determined by a novel combination of racemic protein crystallization and radiation‐damage‐induced phasing (RIP), is reported. Racemic crystals of snakin‐1 and quasi‐racemic crystals incorporating an unnatural 4‐iodophenylalanine residue were prepared from chemically synthesized d ‐ and l ‐proteins. Breakage of the C?I bonds in the quasi‐racemic crystals facilitated structure determination by RIP. The crystal structure reveals a unique protein fold with six disulfide crosslinks, presenting a distinct electrostatic surface that may target the protein to microbial cell surfaces.     

Diverse effect of PEO-PPO-PEO and PPO-PEO-PPO triblock copolymers on temperature responsive behavior of luminescent hard-soft colloids

The present work introduces the interaction of hard and soft colloids in aqueous solutions at various temperatures and concentrations, as well as at critical conditions of temperature induced phase separation. Hard and soft colloids are represented by luminescent silica nanoparticles and aggregates of PEO-PPO-PEO and PPO-PEO-PPO triblock copolymers correspondingly. The formation of the mixed aggregates between hard and soft colloids in equilibrium conditions has been revealed by dynamic light scattering measurements. The distribution of silica nanoparticles between aqueous and surfactant rich phases after phase separation highlights the effect of pH, architecture and concentration of triblock copolymers on the mixed hard-soft colloids aggregation at cloud point conditions. The peculiar aggregation and phase behavior of PPO-PEO-PPO pluronics should be assumed as the main reason of the enhanced mixed aggregation with SNs at increased temperatures and concentrated conditions.     

Controlling the Size and Morphology of Supramolecular Assemblies of Viologen–Resorcin[4]arene Cavitands

A novel class of self‐assembling nanoparticles is formed with viologen–resorcin[4]arene cavitands; the association model is strongly controlled by their hydrophobicity. Interestingly, the cavitand assemblies are designed through click chemistry to form self‐assembled noncovalently connected aggregates through counterion displacement. The iodide and benzoate ions are utilized as strongly polarizable counterions to induce cavitand self‐assembly. The counterion‐mediated decrease in hydrophilicity of the viologen–resorcin[4]arenes is the underlying trigger to induce particle formation. These particles can be used as nanocontainers and find their applications in delivery systems.     

Polysaccharide Hydrogels for the Protection of Dairy-Related Microorganisms in Adverse Environmental Conditions

Adverse environmental conditions are severely limiting the use of microorganisms in food systems, such as probiotic delivery, where low pH causes a rapid decrease in the survival of ingested bacteria, and mixed-culture fermentation, where stepwise changes and/or metabolites of individual microbial groups can hinder overall growth and production. In our study, model probiotic lactic acid bacteria (L. plantarum ATCC 8014, L. rhamnosus GG) and yeasts native to dairy mixed cultures (K. marxianus ZIM 1868) were entrapped in an optimized (cell, alginate and hardening solution concentration, electrostatic working parameters) Ca-alginate system. Encapsulated cultures were examined for short-term survival in the absence of nutrients (lactic acid bacteria) and long-term performance in acidified conditions (yeasts). In particular, the use of encapsulated yeasts in these conditions has not been previously examined. Electrostatic manufacturing allowed for the preparation of well-defined alginate microbeads (180–260 µm diameter), high cell-entrapment (95%) and viability (90%), and uniform distribution of the encapsulated cells throughout the hydrogel matrix. The entrapped L. plantarum maintained improved viabilities during 180 min at pH 2.0 (19% higher when compared to the free culture), whereas, L. rhamnosus appeared to be less robust. The encapsulated K. marxianus exhibited double product yields in lactose- and lactic acid-modified MRS growth media (compared to an unfavorable growth environment for freely suspended cells). Even within a conventional encapsulation system, the pH responsive features of alginate provided superior protection and production of encapsulated yeasts, allowing several applications in lacto-fermented or acidified growth environments, further options for process optimization, and novel carrier design strategies based on inhibitor charge expulsion.     

Thermal stability and secondary structure of feruloylated Rapana thomasiana hemocyanin

Journal of Thermal Analysis and Calorimetry - This is the first report on the conjugation of a hemocyanin from Rapana thomasiana (RtH) with ferulic acid, which itself exhibits an immunostimulatory...