Structural and Functional Studies of Peptide and Protein On Engineered Surfaces/Interfaces

Biomolecular decorated surfaces have shown great potential in many applications ranging from antimicrobial coatings to biosensing and biofuels due to their excellent properties. The performance of such biomolecular functionalized surfaces is largely dependent on the molecular structure of surface immobilized biomolecules, the surfaces used for attachment, and the surrounding environment biomolecules are functioning in. Moreover, maintaining the functions of such biomolecular surfaces in the absence of bulk water is challenging but important for extending the applications of such surfaces to non-aqueous environment. In order to have an in-depth understanding of how such biomolecule immobilized surfaces should be designed with optimized functions, molecular level characterization needs to be done to reveal the structures of interfacial biomolecules. Here my thesis research mainly focuses on the investigations of structures (conformations and orientations) of immobilized peptides and proteins at the molecular level using sum frequency generation vibrational spectroscopy (SFG), supplemented by circular dichroism (CD) and attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR). The relations of structures and functions of the biomolecular surfaces are elucidated. I first studied the effect of the immobilization site (e.g., N- or C-terminus) on the structure and activity of surface immobilized antimicrobial peptide (AMP) MSI-78 using a combination of SFG, CD, coarse grained MD simulation, and antibacterial testing. This peptide exhibits similar secondary structure but different orientations when immobilized with different termini, leading to varied antibacterial activity. In order to determine whether a peptide could be engineered to assume a different orientation (standing up instead of lying down), a combined coarse grained MD simulation/SFG approach was developed to design AMPs with controlled orientations after surface immobilization. To extend this research into more complicated systems, surfaces immobilized with enzymes were characterized using SFG and coarse grained MD simulation. Results show that not only can the orientation of these immobilized enzymes be controlled by selecting the surface immobilization site, but this surface orientation can dictate the enzymatic activity. The enzymatic activity is also affected by the property of the underlined surface for enzyme immobilization. With a more hydrophilic surface, a better enzymatic activity was observed. Thirdly, methods of retaining the structure and function of immobilized biomolecules in the absence of bulk water were developed. Both native secondary structure and orientation of surface immobilized biomolecules can be retained and controlled by physically attached sugar coatings and chemically co-immobilized poly-saccharide molecules. Chemically tethered sugar was found to be able to enhance the antibacterial activity of immobilized AMPs in dry conditions. Lastly, the interfacial structures of protein therapeutics adsorbed at the silicone oil surface are characterized by SFG. SFG signals contributed by both alpha helical and beta sheet structures were observed from proteins at the silicone oil surfaces. Nonionic surfactants are effective on reducing protein aggregations at such surfaces. This thesis is collaborative in nature. Prof. Neil Marsh’s group performed the enzyme engineering, and Prof. Charlie Brooks’ group carried out the simulation. The antimicrobial activity measurements were done by Prof. Chuanwu Xi’s group and Prof. Nick Abbott’s group. The CVD coatings were made by Prof. Joerg Lahann’s group. This thesis provides a detailed and systematic study of how peptides and proteins behave on abiotic surfaces in different chemical environments. Methodologies on how to retain the structure and enhance the activity of surface immobilized peptides and proteins in the absence of bulk water have been developed.PHDChemistryUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttps://deepblue.lib.umich.edu/bitstream/2027.42/138790/1/yaoxin_1.pd

The volatile anesthetic isoflurane differentially inhibits voltage-gated sodium channel currents between pyramidal and parvalbumin neurons in the prefrontal cortex

BackgroundHow volatile anesthetics work remains poorly understood. Modulations of synaptic neurotransmission are the direct cellular mechanisms of volatile anesthetics in the central nervous system. Volatile anesthetics such as isoflurane may reduce neuronal interaction by differentially inhibiting neurotransmission between GABAergic and glutamatergic synapses. Presynaptic voltage-dependent sodium channels (Nav), which are strictly coupled with synaptic vesicle exocytosis, are inhibited by volatile anesthetics and may contribute to the selectivity of isoflurane between GABAergic and glutamatergic synapses. However, it is still unknown how isoflurane at clinical concentrations differentially modulates Nav currents between excitatory and inhibitory neurons at the tissue level.MethodsIn this study, an electrophysiological recording was applied in cortex slices to investigate the effects of isoflurane on Nav between parvalbumin (PV+) and pyramidal neurons in PV-cre-tdTomato and/or vglut2-cre-tdTomato mice.ResultsIsoflurane at clinically relevant concentrations produced a hyperpolarizing shift in the voltage-dependent inactivation and slowed the recovery time from the fast inactivation in both cellular subtypes. Since the voltage of half-maximal inactivation was significantly depolarized in PV+ neurons compared to that of pyramidal neurons, isoflurane inhibited the peak Nav currents in pyramidal neurons more potently than those of PV+ neurons (35.95 ± 13.32% vs. 19.24 ± 16.04%, P = 0.036 by the Mann-Whitney test).ConclusionsIsoflurane differentially inhibits Nav currents between pyramidal and PV+ neurons in the prefrontal cortex, which may contribute to the preferential suppression of glutamate release over GABA release, resulting in the net depression of excitatory-inhibitory circuits in the prefrontal cortex

Two types of zero Hall phenomena in few-layer MnBi2_2Te4_4

The van der Waals antiferromagnetic topological insulator MnBi$_2$Te$_4$ represents a promising platform for exploring the layer-dependent magnetism and topological states of matter. Despite the realization of several quantized phenomena, such as the quantum anomalous Hall effect and the axion insulator state, the recently observed discrepancies between magnetic and transport properties have aroused controversies concerning the topological nature of MnBi$_2$Te$_4$ in the ground state. Here, we demonstrate the existence of two distinct types of zero Hall phenomena in few-layer MnBi$_2$Te$_4$. In addition to the robust zero Hall plateau associated with the axion insulator state, an unexpected zero Hall phenomenon also occurs in some odd-number-septuple layer devices. Importantly, a statistical survey of the optical contrast in more than 200 MnBi$_2$Te$_4$ reveals that such accidental zero Hall phenomenon arises from the reduction of effective thickness during fabrication process, a factor that was rarely noticed in previous studies of 2D materials. Our finding not only resolves the controversies on the relation between magnetism and anomalous Hall effect in MnBi$_2$Te$_4$, but also highlights the critical issues concerning the fabrication and characterization of devices based on 2D materials.Comment: 21 pages, 4 figure

Research progress of chilled meat freshness detection based on nanozyme sensing systems

peer reviewedIt is important to develop rapid, accurate, and portable technologies for detecting the freshness of chilled meat to meet the current demands of meat industry. This report introduces freshness indicators for monitoring the freshness changes of chilled meat, and systematically analyzes the current status of existing detection technologies which focus on the feasibility of using nanozyme for meat freshness sensing detection. Furthermore, it examines the limitations and foresees the future development trends of utilizing current nanozyme sensing systems in evaluating chilled meat freshness. Harmful chemicals are produced by food spoilage degradation, including biogenic amines, volatile amines, hydrogen sulfide, and xanthine, which have become new freshness indicators to evaluate the freshness of chilled meat. The recognition mechanisms are clarified based on the special chemical reaction with nanozyme or directly inducting the enzyme-like catalytic activity of nanozyme