Structural determination of model phospholipid membranes by Raman spectroscopy: Laboratory experiment

Interaction of L-phenylalanine with carbonyl groups in mixed lipid membranes

The interaction of L-Phe with the membrane components, i.e., lipids and proteins, has been discussed in the current literature due to the interest to understand the effect of single amino acids in relation to the formation of amyloid aggregates. In the present work, it is shown that L-Phe interacts with 9:1 DMPC (1,2-dimyristoyl-sn-glycero-3 phosphocholine)/DPPC (1,2-dipalmitoyl-sn-glycero-3 phosphocholine) mixtures but not in the 1:9 one. An important observation is that the interaction disappears when DPPC is replaced by diether PC (2-di-O-hexadecyl-sn-glycero-3-phosphocholine) a lipid lacking carbonyl groups (CO). This denotes that CO groups may interact specifically with L-Phe in accordance with the appearance of a new peak observed by Infrared spectroscopy (FTIR-ATR). The interaction of L-Phe affects the compressibility pattern of the 9:1 DMPC/DPPC mixture which is congruent with the changes observed by Raman spectra. The specific interaction of L-Phe with CO, propagates to phosphate and choline groups in this particular mixture as analyzed by FTIR-ATR spectroscopy and is absent when DMPC is dopped with diether PC.

Differential Effects of Soy Isoflavones on the Biophysical Properties of Model Membranes

The effects that the main soy isoflavones, genistein and daidzein, have upon the biophysical properties of a model lipid bilayer composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) or DOPC with cholesterol (4 to 1 mol ratio) have been investigated by transbilayer water permeability, differential scanning calorimetry, and confocal Raman microspectroscopy. Genistein is found to increase water permeability, decrease phase transition temperature, reduce enthalpy of transition, and induce packing disorder in the DOPC membrane with an increasing concentration. On the contrary, daidzein decreases water permeability and shows negligible impact on thermodynamic parameters and packing disorder at comparable concentrations. For a cholesterol-containing DOPC bilayer, both genistein and daidzein exhibit an overall less pronounced effect on transbilayer water permeability. Their respective differential abilities to modify the physical and structural properties of biomembranes with varying lipid compositions signify a complex and sensitive nature to isoflavone interactions, which depends on the initial state of bilayer packing and the differences in the molecular structures of these soy isoflavones, and provide insights in understanding the interactions of these molecules with cellular membranes.

In Situ Monitoring of Membrane Protein Electron Transfer via Surface-Enhanced Resonance Raman Spectroscopy

In situ analysis of membrane protein-ligand interactions under physiological conditions is of significance for both fundamental and applied science, but it is still a big challenge due to the limits in sensitivity and selectivity. Here, we demonstrate the potential of surface-enhanced resonance Raman spectroscopy (SERRS) for the investigation of membrane protein-protein interactions. Lipid biolayers are successfully coated on silver nanoparticles through electrostatic interactions, and a highly sensitive and biomimetic membrane platform is obtained in vitro. Self-assembly and immobilization of the reduced cytochrome b5 on the coated membrane are achieved and protein native biological functions are preserved. Owing to resonance effect, the Raman fingerprint of the immobilized cytochrome b5 redox center is selectively enhanced, allowing for in situ and real-time monitoring of the electron transfer process between cytochrome b5 and their partners, cytochrome c and myoglobin. This study provides a sensitive analytical approach for membrane proteins and paves the way for in situ exploration of their structural basis and functions.

Aspirin Interacts with Cholesterol-Containing Membranes in a pH-Dependent Manner

Aspirin has been used for broad therapeutic treatment, including secondary prevention of cardiovascular disease associated with increased cholesterol levels. Aspirin and other nonsteroidal anti-inflammatory drugs have been shown to interact with lipid membranes and change their biophysical properties. In this study, mixed lipid model bilayers made from 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylcholine (POPC) or 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) comprising varying concentrations of cholesterol (10:1, 4:1, and 1:1 mole ratio of lipid:chol), prepared by the droplet interface bilayer method, were used to examine the effects of aspirin at various pH on transbilayer water permeability. The presence of aspirin increases the water permeability of POPC bilayers in a concentration-dependent manner, with a greater magnitude of increase at pH 3 compared to pH 7. In the presence of cholesterol, aspirin is similarly shown to increase water permeability; however, the extent of the increase depends on both the concentration of cholesterol and the pH, with the least pronounced enhancement in water permeability at high cholesterol levels at pH 7. A fusion of data from differential scanning calorimetry, confocal Raman microspectrophotometry, and interfacial tensiometric measurements demonstrates that aspirin can promote significant thermal, structural, and interfacial property perturbations in the mixed-lipid POPC or DOPC membranes containing cholesterol, indicating a disordering effect on the lipid membranes. Our findings suggest that aspirin fluidizes phosphocholine membranes in both cholesterol-free and cholesterol-enriched states and that the overall effect is greater when aspirin is in a neutral state. These results confer a deeper comprehension of the divergent effects of aspirin on biological membranes having heterogeneous compositions, under varying physiological pH and different cholesterol compositions, with implications for a better understanding of the gastrointestinal toxicity induced by the long term use of this important nonsteroidal anti-inflammatory molecule.

QR code technology in individual identification training provides an introduction in hands-on forensic DNA genotyping to medical students

BACKGROUND

Forensic biology is a subject in the field of forensic science that stresses practical teaching and training in laboratory skills. Visualization of deoxyribonucleic acid (DNA) profiles is important in individual identification and is easily performed by well-trained examiners. Therefore, developing a novel training project for obtaining individual DNA profiles can improve the quality of teaching for medical students or trainees. DNA profiles based on quick response (QR) codes can also be applied to practical teaching and operation training for individual identification.

METHODS

A novel training project was developed through an experimental course in forensic biology. Blood samples and buccal swabs with oral epithelial cells, as used in the forensic DNA laboratory, were obtained from medical students at Fujian Medical University. DNA was isolated, and a number of short tandem repeat (STR) loci were used as genetic markers to generate DNA profiles. The students converted DNA profiles and individual information into a QR code. The QR code could then be scanned by a mobile phone for consulting and retrieval. Gene identity cards with QR codes were produced and provided to every student. The participation rate and passing rate of students who participated in the novel training project were calculated and compared with those of students in the traditional experimental course, and a chi-square test was carried out by SPSS 23.0 software to evaluate the teaching effectiveness. p < 0.05 indicated significant differences. In addition, a survey was conducted to investigate the likelihood of using of gene identity cards with QR codes in the future.

RESULTS

A total of 54 of 91 medical students who studied forensic biology participated in the novel training project in 2021. Only 31 of 78 students who studied forensic biology participated in the traditional experimental course in 2020. The participation rate in the novel training project was 24% higher than that of the traditional experimental course. The participants in the novel training project showed better performance in forensic biological handling techniques. The passing rate of the students in the forensic biology course with the novel training project was approximately 17% higher than that of the students in the former course. The participation rates and passing rates of the two groups were significantly different (χ = 6.452, p = 0.008 and χ = 11.043, p = 0.001). In the novel training project, all participants made 54 gene identity cards with QR codes. Furthermore, in the DNA profiles of four African students who participated, we found two rare alleles that were not discovered in Asians. The survey showed that the use of gene identity cards with QR codes was accepted by most participants, and the likelihood of future utilization was 78%.

CONCLUSION

We established a novel training project to promote the learning activities of medical students in experimental forensic biology courses. The participants showed great interest in using gene identity cards with QR codes to store general individual identity information and DNA profiles. They also examined the genetic population differences between different races based on DNA profiles. Hence, the novel training project could be useful for training workshops, forensic experimental courses, and medical big data research.