MANIPULATION OF LIGHT VIA SUBWAVELENGTH NANOSTRUCTURES

Ph.DDOCTOR OF PHILOSOPH

Asynchronous switching control for fuzzy Markov jump systems with periodically varying delay and its application to electronic circuits

This article focuses on addressing the issue of asynchronous H∞ control for Takagi-Sugeno (T-S) fuzzy Markov jump systems with generally incomplete transition probabilities (TPs). The delay is assumed to vary periodically, resulting in one monotonically increasing interval and one monotonically decreasing interval during each period. Meanwhile, a new Lyapunov-Krasovskii functional (LKF) is devised, which depends on membership functions (MFs) and two looped functions formulated for the monotonic intervals. Since the modes and TPs of the original system are assumed to be unavailable, an asynchronous switching fuzzy controller on the basis of hidden Markov model is proposed to stabilize the fuzzy Markov jump systems (FMJSs) with generally incomplete TPs. Consequently, a stability criterion with improved practicality and reduced conservatism is derived, ensuring the stochastic stability and H∞ performance of the closed-loop system. Finally, this technique is employed to the tunnel diode circuit system, and a comparison example is given, which verifies the practicality and superiority of the method

THE PROBLEM OF THE RELATIONSHIP OF SCIENCE AND RELIGION IN THE SYSTEM OF SECULAR GENERAL EDUCATION

The relationship between science and religion throughout history ranged from opposition to their unity. The long-standing prevalence of theology over science has caused a counter-atheistic reaction, which has grown into the absolutization of science in all spheres of life. The introduction to the secular general education of the course “Fundamentals of Religious Cultures and Secular Ethics” was ambiguously accepted by society. The author substantiates the position that science and religion are not mutually exclusive, but rather can complement each other, forming a unified picture of the world among the younger generation.Взаимоотношения науки и религии на протяжении всей истории выстраивались от противопоставления до их единства. Многолетнее преобладание богословия над наукой вызвало встречную атеистическую реакцию, переросшую в абсолютизацию науки во всех сферах бытия. Введение в светское общее образование курса «Основы религиозных культур и светской этики» было неоднозначно воспринято обществом. Автор обосновывает позицию, что наука и религия не взаимно исключают друг друга, а напротив, могут дополнять друг друга, формируя у подрастающего поколения единую картину мира

Structure of a cereal purple acid phytase provides new insights to phytate degradation in plants

Grain phytate, a mixed metal ion salt of inositol hexakisphosphate, accounts for 60%–80% of stored phosphorus in plants and is a potent antinutrient of non-ruminant animals including humans. Through neofunctionalization of purple acid phytases (PAPhy), some cereals such as wheat and rye have acquired particularly high mature grain phytase activity. As PAPhy activity supplies phosphate, liberates metal ions necessary for seedling emergence, and obviates antinutrient effects of phytate, its manipulation and control are targeted crop traits. Here we show the X-ray crystal structure of the b2 isoform of wheat PAPhy induced during germination. This high-resolution crystal structure suggests a model for phytate recognition that, validated by molecular dynamics simulations, implicates elements of two sequence inserts (termed PAPhy motifs) relative to a canonical metallophosphoesterase (MPE) domain in forming phytate-specific substrate specificity pockets. These motifs are well conserved in PAPhys from monocot cereals, enzymes which are characterized by high specificity for phytate. Tested by mutagenesis, residues His229 in PAPhy motif 4 and Lys410 in the MPE domain, both conserved in PAPhys, are found to strongly influence phytase activity. These results explain the observed phytase activity of cereal PAPhys and open the way to the rational engineering of phytase activity in planta

BamA β16C strand and periplasmic turns are critical for outer membrane protein insertion and assembly

Outer membrane β-barrel proteins play important roles in importing nutrients, exporting wastes and conducting signals in Gram-negative bacteria, mitochondria and chloroplasts. The outer membrane proteins are inserted and assembled into the outer membrane by OMP85 family proteins. In Escherichia coli , the b-barrel assembly machinery (BAM) contains four lipoproteins BamB, BamC, BamD and BamE, and one outer membrane protein BamA, forming a "top hat"-like structure. Structural and functional studies of the E. coli BAM machinery have revealed that the rotation of periplasmic ring may trigger the barrel b1C-b6C scissor-like movement that promote the unfolded outer membrane protein insertion without using ATP. Here we report the BamA C-terminal barrel structure of Salmonella enterica Typhimurium str. LT2 and functional assays, which reveal that the BamA's C-terminal residue Trp, the b16C strand of the barrel and the periplasmic turns are critical for the functionality of BamA. These findings indicate that the unique b16C and the periplasmic turns of BamA are important for the out membrane insertion and assembly. The periplasmic turns might mediate the rotation of the periplasmic ring to the scissor-like movement of BamA b1C-b6C, triggering the outer membrane protein insertion. These results are important for understanding the outer membrane protein insertion in Gram-negative bacteria, as well as in mitochondria and chloroplasts

Diversification in the inositol tris/tetrakisphosphate kinase (ITPK) family: crystal structure and enzymology of the outlier AtITPK4

Myo-inositol tris/tetrakisphosphate kinases (ITPKs) catalyze diverse phosphotransfer reactions with myo-inositol phosphate and myo-inositol pyrophosphate substrates. However, the lack of structures of nucleotide-coordinated plant ITPKs thwarts a rational understanding of phosphotransfer reactions of the family. Arabidopsis possesses a family of four ITPKs of which two isoforms, ITPK1 and ITPK4, control inositol hexakisphosphate and inositol pyrophosphate levels directly or by provision of precursors. Here, we describe the specificity of Arabidopsis ITPK4 to pairs of enantiomers of diverse inositol polyphosphates and show how substrate specificity differs from Arabidopsis ITPK1. Moreover, we provide a description of the crystal structure of ATP-coordinated AtITPK4 at 2.11 Å resolution that, along with a description of the enantiospecificity of the enzyme, affords a molecular explanation for the diverse phosphotransferase activity of this enzyme. That Arabidopsis ITPK4 has a KM for ATP in the tens of micromolar range, potentially explains how, despite the large-scale abolition of InsP6, InsP7 and InsP8 synthesis in Atitpk4 mutants, Atitpk4 lacks the phosphate starvation responses of Atitpk1 mutants. We further demonstrate that Arabidopsis ITPK4 and its homologues in other plants possess an N-terminal haloacid dehalogenase-like fold not previously described. The structural and enzymological information revealed will guide elucidation of ITPK4 function in diverse physiological contexts, including InsP8-dependent aspects of plant biology

Lipopolysaccharide is Inserted into the Outer Membrane through An Intramembrane Hole, A Lumen Gate, and the Lateral Opening of LptD

Lipopolysaccharide (LPS) is essential for the vitality of most Gram-negative bacteria and plays an important role in bacterial multidrug resistance. The LptD/E translocon inserts LPS into the outer leaflet, the mechanism of which is poorly understood. Here, we report mutagenesis, functional assays, and molecular dynamics simulations of the LptD/E complex, which suggest two distinct pathways for the insertion of LPS. The N-terminal domain of LptD comprises a hydrophobic slide that injects the acyl tails of LPS directly into the outer membrane through an intramembrane hole, while the core oligosaccharide and O-antigen pass a lumen gate that triggers the unzipping of the lateral opening between strands β1C and β26C of the barrel of LptD, to finalize LPS insertion. Mutation of the LPS transport related residues or block of the LPS transport pathways results in the deaths of Escherichia coli. These findings are important for the development of novel antibiotics

Structural basis of outer membrane protein insertion by the BAM complex

All Gram-negative bacteria, mitochondria and chloroplasts have outer membrane proteins (OMPs) that perform many fundamental biological processes. The OMPs in Gram-negative bacteria are inserted and folded into the outer membrane by the β-barrel assembly machinery (BAM). The mechanism involved is poorly understood, owing to the absence of a structure of the entire BAM complex. Here we report two crystal structures of the Escherichia coli BAM complex in two distinct states: an inward-open state and a lateral-open state. Our structures reveal that the five polypeptide transport-associated domains of BamA form a ring architecture with four associated lipoproteins, BamB–BamE, in the periplasm. Our structural, functional studies and molecular dynamics simulations indicate that these subunits rotate with respect to the integral membrane β-barrel of BamA to induce movement of the β-strands of the barrel and promote insertion of the nascent OMP

Mesenchymal stem cells and nano-structured surfaces

Mesenchymal stem cells (MSCs) represent multipotent stromal cells that can differentiate into a variety of cell types, including osteoblasts (bone cells), chondrocytes (cartilage cells), and adipocytes (fat cells). Their multi-potency provides a great promise as a cell source for tissue engineering and cell-based therapy for many diseases, particularly bone diseases and bone formation. To be able to direct and modulate the differentiation of MSCs into the desired cell types in situ in the tissue, nanotechnology is introduced and used to facilitate or promote cell growth and differentiation. These nano-materials can provide a fine structure and tuneable surface in nanoscales to help the cell adhesion and promote the cell growth and differentiation of MSCs. This could be a dominant direction in future for stem cells based therapy or tissue engineering for various diseases. Therefore, the isolation, manipulation, and differentiation of MSCs are very important steps to make meaningful use of MSCs for disease treatments. In this chapter, we have described a method of isolating MSC from human bone marrow, and how to culture and differentiate them in vitro. We have also provided research methods on how to use MSCs in an in vitro model and how to observe MSC biological response on the surface of nano-scaled materials