INTEGRATED NANOSCALE IMAGING AND SPATIAL RECOGNITION OF BIOMOLECULES ON SURFACES

Biomolecules on cell surfaces play critical roles in diverse biological and physiological processes. However, conventional bulk scale techniques are unable to clarify the density and distribution of specific biomolecules in situ on single, living cell surfaces at the micro or nanoscale. In this work, a single cell analysis technique based on Atomic Force Microscopy (AFM) is developed to spatially identify biomolecules and characterize nanomechanical properties on single cell surfaces. The unique advantage of these AFM-based techniques lies in the ability to operate in situ (in a non-destructive fashion) and in real time, under physiological conditions or controlled micro-environments. First, AFM-based force spectroscopy was developed to study the fundamental biophysics of the heparin/thrombin interaction at the molecular level. Based on force spectroscopy, a force recognition mapping strategy was developed and optimized to spatially detect single protein targets on non-biological surfaces. This platform was then translated to the study of complex living cell surfaces. Specific carbohydrate compositions and changes in their distribution, as well as elasticity change were obtained by monitoring Bacillus cells sporulation process. The AFM-based force mapping technique was applied to different cellular systems to develop a cell surface biomolecule library. Nanoscale imaging combined with carbohydrate mapping was used to evaluate inactivation methods and growth temperatures effects on Yersinia pestis surface. A strategy to image cells in real time was coupled with hydrophobicity mapping technique to monitor the effect of antimicrobials (antimicrobial polymer and copper) on Escherichia coli and study their killing mechanisms. The single spore hydrophobicity mapping was used to localize the exosporium structure and potentially reconstruct culture media. The descriptions of cell surface DNA on single human epithelial cells potentially form a novel tool for forensic identification. Overall, these nanoscale tools to detect and assess changes in cell behavior and function over time, either as a result of natural state changes or when perturbed, will further our understanding of fundamental biological processes and lead to novel, robust methods for the analysis of individual cells. Real time analysis of cells can be used for the development of lab-on-chip type assays for drug design and testing or to test the efficacy of antimicrobials

The Turtle Garden: Tan Kah Kee’s last spiritual world

This paper explores the role of diasporic subjects in China’s heritage-making through a case study of the Turtle Garden built by Tan Kah Kee in Xiamen, China. Tan is the first person with Overseas Chinese background who built museums in the P.R. China and has been regarded as a symbol of Overseas Chinese patriotism. This paper argues that the Turtle Garden, conceptualised as a postcolonial ‘carnivalesque’ space, is more than a civic museum for public education. It reflects the owner’s highly complex and sometimes conflicting museum outlook embedded in his life experience as a migrant, his encounter with (British) colonialism in Malaya, and integrated with his desire and despair about the Chinese Communist Party’s nation-building project in the 1950s. Rather than a sign of devotion to the socialist motherland as simplistically depicted in China’s discourse, the garden symbolises Tan’s last ‘spiritual world’ where he simultaneously engaged with soul-searching as a returned Overseas Chinese and alternative diasporic imagining of Chinese identities and nation. It brings to light the value of heritage-making outside centralised heritage discourses, and offers an invaluable analytical lens to disentangle the contested and ever shifting relationship between diasporic subjects, cultural heritage and nation-(re)building in the Chinese context and beyond

Evaluating interaction forces between BSA and rabbit anti-BSA in sulphathiazole sodium, tylosin and levofloxacin solution by AFM

Protein-protein interactions play crucial roles in numerous biological processes. However, it is still challenging to evaluate the protein-protein interactions, such as antigen and antibody, in the presence of drug molecules in physiological liquid. In this study, the interaction between bovine serum albumin (BSA) and rabbit anti-BSA was investigated using atomic force microscopy (AFM) in the presence of various antimicrobial drugs (sulphathiazole sodium, tylosin and levofloxacin) under physiological condition. The results show that increasing the concentration of tylosin decreased the single-molecule-specific force between BSA and rabbit anti-BSA. As for sulphathiazole sodium, it dramatically decreased the specific force at a certain critical concentration, but increased the nonspecific force as its concentration increasing. In addition, the presence of levofloxacin did not greatly influence either the specific or nonspecific force. Collectively, these results suggest that these three drugs may adopt different mechanisms to affect the interaction force between BSA and rabbit anti-BSA. These findings may enhance our understanding of antigen/antibody binding processes in the presence of drug molecules, and hence indicate that AFM could be helpful in the design and screening of drugs-modulating protein-protein interaction processes

Mechanism of Inhibition of the GluA2 AMPA Receptor Channel Opening by Talampanel and Its Enantiomer: The Stereochemistry of the 4‑Methyl Group on the Diazepine Ring of 2,3-Benzodiazepine Derivatives

Stereoselectivity of 2,3-benzodiazepine compounds provides a unique way for the design of stereoisomers as more selective and more potent inhibitors as drug candidates for treatment of the neurological diseases involving excessive activity of AMPA receptors. Here we investigate a pair of enantiomers known as Talampanel and its (+) counterpart about their mechanism of inhibition and selectivity toward four AMPA receptor subunits or GluA1–4. We show that Talampanel is the eutomer with the endismic ratio being 14 for the closed-channel and 10 for the open-channel state of GluA2. Kinetic evidence supports that Talampanel is a noncompetitive inhibitor and it binds to the same site for those 2,3-benzodiazepine compounds with the C-4 methyl group on the diazepine ring. This site, which we term as the “M” site, recognizes preferentially those 2,3-benzodiazepine compounds with the C-4 methyl group being in the <i>R</i> configuration, as in the chemical structure of Talampanel. Given that Talampanel inhibits GluA1 and GluA2, but is virtually ineffective on the GluA3 and GluA4 AMPA receptor subunits, we hypothesize that the “M” site(s) on GluA1 and GluA2 to which Talampanel binds is different from that on GluA3 and GluA4. If the molecular properties of the AMPA receptors and Talampanel are used for selecting an inhibitor as a single drug candidate for controlling the activity of all AMPA receptors in vivo, Talampanel is not ideal. Our results further suggest that addition of longer acyl groups to the N-3 position should produce more potent 2,3-benzodiazepine inhibitors for the “M” site

Mechanism of Inhibition of the GluA1 AMPA Receptor Channel Opening by the 2,3-Benzodiazepine Compound GYKI 52466 and a <i>N</i>‑Methyl-Carbamoyl Derivative

2,3-Benzodiazepine derivatives, also known as GYKI compounds, represent a group of the most promising synthetic inhibitors of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors. Here we investigate the mechanism of inhibition of the GluA1 channel opening and the site of inhibition by GYKI 52466 and its N-3 methyl-carbamoyl derivative, which we term as BDZ-<i>f</i>. GluA1 is a key AMPA receptor subunit involved in the brain function. Excessive activity and elevated expression of GluA1, however, has been implicated in a number of neurological disorders. Using a laser-pulse photolysis technique, which provides ∼60 μs resolution, we measured the effect of these inhibitors on the rate of GluA1 channel opening and the amplitude of the glutamate-induced whole-cell current. We found that both compounds inhibit GluA1 channel noncompetitively. Addition of an N-3 methyl-carbamoyl group to the diazepine ring with the azomethine feature (i.e., GYKI 52466) improves the potency of the resulting compound or BDZ-<i>f</i> without changing the site of binding. This site, which we previously termed as the “M” site on the GluA2 AMPA receptor subunit, therefore favorably accommodates an N-3 acylating group. On the basis of the magnitude of the inhibition constants for the same inhibitors but different receptors, the “M” sites on GluA1 and GuA2 are different. Overall, the “M” site or the binding environment on GluA2 accommodates the same compounds better, or the same inhibitors show stronger potency on GluA2, as we have reported previously [Wang et al. Biochemistry (2011) 50, 7284−7293]. However, acylating the N-3 position to occupy the N-3 side pocket of the “M” site can significantly narrow the difference and improve the potency of a resulting compound on GluA1