Role of a secondary coordination sphere residue in halogenation catalysis of non-heme iron enzymes

Chemo- and regio-selective catalysis of C(sp3)-H halogenation reaction is a formidable goal in chemical synthesis. 2-oxo-glutarate (2OG) dependent non-heme iron halogenases catalyze selective chlorination/bromination of C-H bonds and exhibit high sequence and structural similarities with non-heme iron hydroxylases. How the secondary coordination sphere (SCS) of these two enzyme systems differentiate and determine their reactivity is not understood. In this work, we show that tyrosine placement in the SCS of non-heme iron halogenases have a huge impact on their structure, function, and reactivity. We discover that a tyrosine mutant (F121Y) in SyrB2 halogenase undergoes post-translational oxidation to dihydroxyphenylalanine (DOPA) physiologically. A combination of spectroscopic, mass-spectrometric, and biochemical studies show that the DOPA modification in SyrB2 renders the enzyme non-functional. Further bioinformatics analysis suggests that halogenases, unlike hydroxylases, have a conserved placement of phenylalanine at position 121 to preclude such unproductive oxidation. Overall, this study demonstrates the importance of the SCS in controlling the structure and enzymatic activity of non-heme iron halogenases. Our results will have significant implications towards the design of small-molecule and protein-based halogenation catalysts

Lipid Corona Formation from Nanoparticle Interactions with Bilayers and Membrane-Specific Biological Outcomes

While mixing nanoparticles with certain biological molecules can result in coronas that afford some control over how engineered nanomaterials interact with living systems, corona formation mechanisms remain enigmatic. Here, we report spontaneous lipid corona formation, i.e. without active mixing, upon attachment to stationary lipid bilayer model membranes and bacterial cell envelopes, and present ribosome-specific outcomes for multi-cellular organisms. Experiments show that polycation-wrapped particles disrupt the tails of zwitterionic lipids, increase bilayer fluidity, and leave the membrane with reduced ζ-potentials. Computer simulations show contact ion pairing between the lipid headgroups and the polycations’ ammonium groups leads to the formation of stable, albeit fragmented, lipid bilayer coronas, while microscopy shows fragmented bilayers around nanoparticles after interacting with Shewanella oneidensis. Our mechanistic insight can be used to improve control over nano-bio interactions and to help understand why some nanomaterial/ligand combinations are detrimental to organisms, like Daphnia magna, while others are not. </a

Lipid Corona Formation from Nanoparticle Interactions with Bilayers and Membrane-Specific Biological Outcomes

<a></a><a>While mixing nanoparticles with certain biological molecules can result in coronas that afford some control over how engineered nanomaterials interact with living systems, corona formation mechanisms remain enigmatic. Here, we report spontaneous lipid corona formation, i.e. without active mixing, upon attachment to stationary lipid bilayer model membranes and bacterial cell envelopes, and present ribosome-specific outcomes for multi-cellular organisms. Experiments show that polycation-wrapped particles disrupt the tails of zwitterionic lipids, increase bilayer fluidity, and leave the membrane with reduced ζ-potentials. Computer simulations show contact ion pairing between the lipid headgroups and the polycations’ ammonium groups leads to the formation of stable, albeit fragmented, lipid bilayer coronas, while microscopy shows fragmented bilayers around nanoparticles after interacting with <i>Shewanella oneidensis</i>. Our mechanistic insight can be used to improve control over nano-bio interactions and to help understand why some nanomaterial/ligand combinations are detrimental to organisms, like <i>Daphnia magna</i>, while others are not. </a