Chiral Vibrational Structures of Proteins at Interfaces Probed by Sum Frequency Generation Spectroscopy

We review the recent development of chiral sum frequency generation (SFG) spectroscopy and its applications to study chiral vibrational structures at interfaces. This review summarizes observations of chiral SFG signals from various molecular systems and describes the molecular origins of chiral SFG response. It focuses on the chiral vibrational structures of proteins and presents the chiral SFG spectra of proteins at interfaces in the C-H stretch, amide I, and N-H stretch regions. In particular, a combination of chiral amide I and N-H stretches of the peptide backbone provides highly characteristic vibrational signatures, unique to various secondary structures, which demonstrate the capacity of chiral SFG spectroscopy to distinguish protein secondary structures at interfaces. On the basis of these recent developments, we further discuss the advantages of chiral SFG spectroscopy and its potential application in various fields of science and technology. We conclude that chiral SFG spectroscopy can be a new approach to probe chiral vibrational structures of protein at interfaces, providing structural and dynamic information to study in situ and in real time protein structures and dynamics at interfaces

Study on Deepening Agricultural Further Education Innovation and Pushing Forward the Development of Agricultural, Rural Area and Farmers

This presentation was part of the session : Policy Support: Examination for Policies to Promote Continuing Engineering EducationIACEE 11th World Conference on Continuing Engineering EducationZhang Mingpei is the president of Guangxi Agriculture Department. His other positions include: president of leading group of Professional Title Reform of Guangxi Agricultural series, president of Guangxi Agricultural Association. He obtained a postgraduate diploma in “Modern Economy” at Guangxi Teachers Education University. He is a Senior Economist. Wang Zhuguang is the director of Personnel Affairs Section of Guangxi Agriculture Department, and the director of leading group of Professional Titles Reform of Guangxi Agricultural series. She graduated from Guangxi Teachers Education University, majored in Chinese Language and Literature. Wei Hongyan is a Senior Economist in Guangxi Agriculture Department, and a member of Guangxi Talents Society. He obtained a postgraduate diploma in “Macroeconomic” at the Public Management College of Guangxi University. Wei Guirong is the vice-director of Personnel Affairs Section of Guangxi Agriculture Department, and the office vice-director of leading group of Professional Title Reform of Guangxi Agricultural series.This paper expounds the characteristics, the importance and the necessity of continuing education, and analyzes the guidelines, the objectives, the training system and modes of agricultural continuing education (ACE). In the end, it puts forward the basic approaches and measures for ACE reform.Distance Learning and Professional Education ; International Association for Continuing Engineering Educatio

Chiral Sum Frequency Generation for In Situ Probing Proton Exchange in Antiparallel β-Sheets at Interfaces

Studying hydrogen/deuterium (H/D) exchange in proteins can provide valuable insight on protein structure and dynamics. Several techniques are available for probing H/D exchange in the bulk solution, including NMR, mass spectroscopy, and Fourier transform infrared spectroscopy. However, probing H/D exchange at interfaces is challenging because it requires surface-selective methods. Here, we introduce the combination of in situ chiral sum frequency generation (cSFG) spectroscopy and ab initio simulations of cSFG spectra as a powerful methodology to probe the dynamics of H/D exchange at interfaces. This method is applied to characterize H/D exchange in the antiparallel β-sheet peptide LK7β. We report here for the first time that the rate of D-to-H exchange is about 1 order of magnitude faster than H-to-D exchange in the antiparallel structure at the air/water interface, which is consistent with the existing knowledge that O–H/D dissociation in water is the rate-limiting step, and breaking the O–D bond is slower than breaking the O–H bond. The reported analysis also provides fundamental understanding of several vibrational modes and their couplings in peptide backbones that have been difficult to characterize by conventional methods, including Fermi resonances of various combinations of peptide vibrational modes such as amide I and amide II, C–N stretch, and N–H/N–D bending. These results demonstrate cSFG as a sensitive technique for probing the kinetics of H/D exchange in proteins at interfaces, with high signal-to-noise N–H/N–D stretch bands that are free of background from the water O–H/O–D stretch

Characterization of Surface-Active Biofilm Protein BslA in Self-Assembling Langmuir Monolayer at the Air-Water Interface

Biofilm is an extracellular matrix of bacteria and serves as a protective shield of bacterial communities. It is crucial for microbial growth and one of the leading causes of human chronic infections as well. However, the structures and molecular mechanism of biofilm formation remain largely unknown. Here, we examined a protein, BslA, expressed in the biofilms of Bacillus subtilis. We characterized the Langmuir monolayers of BslA at the air/water interface. Using techniques in surface chemistry and spectroscopy, we found that BslA forms a stable and robust Langmuir monolayer at the air/water interface. Our results show that the BslA Langmuir monolayer underwent two-stage elasticity in the solid state phase upon mechanical compression: one is possibly due to the intermolecular interaction and the other is likely due to both the intermolecular compulsion and the intramolecular distortion. The Langmuir monolayer of BslA shows abrupt changes in rigidities and elasticities at ∼25 mN/m. This surface pressure is close to the one at which BlsA saturates the air/water interface as a self-assembled film without mechanical compression, corresponding to a mean molecular area of ∼700 Å per molecule. Based on the results of surface UV-visible spectroscopy and infrared reflective-absorption spectroscopy, we propose that the BslA Langmuir monolayer carries intermolecular elasticity before ∼25 mN/m and both intermolecular and intramolecular elasticity after ∼25 mN/m. These results provide valuable insights into the understanding of biofilm-associated protein under high mechanical force, shedding light on further investigation of biofilm structure and functionalities

C–H Stretch for Probing Kinetics of Self-Assembly into Macromolecular Chiral Structures at Interfaces by Chiral Sum Frequency Generation Spectroscopy

Self-assembly of molecules into chiral macromolecular and supramolecular structures at interfaces is important in various fields, such as biomedicine, polymer sciences, material sciences, and supramolecular chemistry. However, probing the kinetics at interfaces remains challenging because it requires a real-time method that has selectivity to both interface and chirality. Here, we introduce an <i>in situ</i> approach of using the C–H stretch as a vibrational probe detected by chiral sum frequency generation spectroscopy (cSFG). We showed that the C–H stretch cSFG signals of an amphiphilic peptide (LK₇β) can reveal the kinetics of its self-assembly into chiral β-sheet structures at the air–water interface. The cSFG experiments in conjunction with measurements of surface pressure allow us to propose a mechanism of the self-assembly process, which involves an immediate adsorption of disordered structures followed by a lag phase before the self-assembly into chiral antiparallel β-sheet structures. Our method of using the C–H stretch signals implies a general application of cSFG to study the self-assembly of bioactive, simple organic, and polymeric molecules into chiral macromolecular and supramolecular structures at interfaces, which will be useful in tackling problems, such as protein aggregation, rational design of functional materials, and fabrication of molecular devices

Characterization of Parallel β-Sheets at Interfaces by Chiral Sum Frequency Generation Spectroscopy

Characterization of protein secondary structures at interfaces is still challenging due to the limitations of surface-selective optical techniques. Here, we address the challenge of characterizing parallel β-sheets by combining chiral sum frequency generation (SFG) spectroscopy and computational modeling. We focus on human islet amyloid polypeptide aggregates and a de novo designed short polypeptide at lipid/water and air/glass interfaces. We find that parallel β-sheets adopt distinct orientations at various interfaces and exhibit characteristic chiroptical responses in the amide I and N–H stretch regions. Theoretical analysis indicates that the characteristic chiroptical responses provide valuable information on the symmetry, orientation, and vibrational couplings of parallel β-sheet at interfaces

Chiral Sum Frequency Generation for In Situ Probing Proton Exchange in Antiparallel β‑Sheets at Interfaces

Studying hydrogen/deuterium (H/D) exchange in proteins can provide valuable insight on protein structure and dynamics. Several techniques are available for probing H/D exchange in the bulk solution, including NMR, mass spectroscopy, and Fourier transform infrared spectroscopy. However, probing H/D exchange at interfaces is challenging because it requires surface-selective methods. Here, we introduce the combination of in situ chiral sum frequency generation (cSFG) spectroscopy and ab initio simulations of cSFG spectra as a powerful methodology to probe the dynamics of H/D exchange at interfaces. This method is applied to characterize H/D exchange in the antiparallel β-sheet peptide LK₇β. We report here for the first time that the rate of D-to-H exchange is about 1 order of magnitude faster than H-to-D exchange in the antiparallel structure at the air/water interface, which is consistent with the existing knowledge that O–H/D dissociation in water is the rate-limiting step, and breaking the O–D bond is slower than breaking the O–H bond. The reported analysis also provides fundamental understanding of several vibrational modes and their couplings in peptide backbones that have been difficult to characterize by conventional methods, including Fermi resonances of various combinations of peptide vibrational modes such as amide I and amide II, C–N stretch, and N–H/N–D bending. These results demonstrate cSFG as a sensitive technique for probing the kinetics of H/D exchange in proteins at interfaces, with high signal-to-noise N–H/N–D stretch bands that are free of background from the water O–H/O–D stretch