Protein interactions and misfolding analyzed by AFM force spectroscopy.

Osteotropic Peptide that differentiates functional domains of the skeleton.

In an effort to improve the efficacy of cancer chemotherapy by intervening into the cellular responses to chemotherapeutic change, we have used adenoviral overexpression of N -methylpurine DNA glycosylase (MPG or ANPG/AAG) in breast cancer cells to study its ability to imbalance base excision repair (BER) and sensitize cancer cells to alkylating agents. Our results show that MPG-overexpressing cells are significantly more sensitive to the alkylating agents methyl methanesulfonate, N -methyl- N ′-nitro- N -nitrosoguanidine, methylnitrosourea, dimethyl sulfate, and the clinical chemotherapeutic temozolomide. Sensitivity is further increased through coadministration of the BER inhibitor methoxyamine, which covalently binds abasic or apurinic/apyrimidinic (AP) sites and makes them refractory to subsequent repair. Methoxyamine reduction of cell survival is significantly greater in cells overexpressing MPG than in control cells, suggesting a heightened production of AP sites that, if made persistent, results in increased cellular toxicity. We further explored the mechanism of MPG-induced sensitivity and found that sensitivity was associated with a significant increase in the number of AP sites and/or single-strand breaks in overexpressing cells, confirming a MPG-driven accumulation of toxic BER intermediates. These data establish transient MPG overexpression as a potential therapeutic approach for increasing cellular sensitivity to alkylating agent chemotherapy.

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Transient adenoviral N-methylpurine DNA glycosylase overexpression imparts chemotherapeutic sensitivity to human breast cancer cells

Chemical and biological characterization of pectin-like polysaccharides from the bark of the Malian medicinal tree Cola cordifolia

Lithium batteries use binders (mostly polymeric) to achieve appropriate mechanical strength of electrodes. The nature of binding between the polymers and the active component, however, is hardly known. In this paper we attempt to establish this nature by using atomic force microscopy (AFM) measurements. In our model study, the interaction between silicon and carboxymethyl cellulose (CMC)—an anode system of considerable practical interest—is studied. We show that, contrary to occasional expectations in the battery community, the use of AFM in such complex systems cannot give direct information about the magnitude of forces between polymer molecules and substrate. Nevertheless, one can use an indirect approach whereby one can tell whether in the particular case strong (e.g. covalent) or weaker (e.g. adsorption) interactions prevail.

/pdf/an-attempt-to-use-atomic-force-microscopy-for-determination-4mq4351wb4.pdf

An attempt to use atomic force microscopy for determination of bond type in lithium battery electrodes

A procedure for direct functionalization of silicon nitride atomic force microscope (AFM) probes with 3-aminopropyltriethoxy silane (APTES) was developed. The probes were modified in vapors of APTES at ambient conditions (AP-tips). The functionalization of tips was monitored by fluorescent microscopy and the force measurements with AFM. AP-tips were derivatized with a non-fluorescent quinoline analog (FQ) which reacts with primary amines to form a strongly fluorescent isoindole. AP-tip fluorescence was significantly higher than control probes. Amino modified tips manifest a strong adhesion to freshly cleaved mica and this behavior is qualitatively similar to the interaction of unmodified silicone nitride probes with AP-mica. The adhesion of AP-tips to mica or AP-mica to unmodified tips decreases as ionic strength increases indicating a dominant electrostatic component of the adhesion effect. This interpretation is supported by the experiments at different pH and the reaction of AP-tips with glutaraldehyde...

Aminomodified Probes for Atomic Force Microscopy

Conventional methods of selecting gene transfected cells by toxic agents may yield ambiguous results. It is difficult to determine whether cell death is due to selection agents or gene transfection, owing to the substantial overlap of the time-courses for both effects. Therefore, to determine transfection-induced cell toxicity, the mammalian expression vector pEGFP-N1 (CLONTECH Lab., Palo Alto, CA, USA) has been modified to the dual-cassette expression vectors named pEGFP-Ks by the relocation of its EGFP expression cassette. We have precisely monitored the cells transfected with this vector on our custom culture dishes, thereby bypassing the need for selection agent or fluorescent cell sorting. This is a useful method to screen genes encoding potential toxic or useful proteins without performing undesirable selection agent and also can be used to monitor the transfected cells for various purposes, either the inhibition or proliferation of mammalian cells for applications in biotechnology.

/pdf/monitoring-transfected-cells-without-selection-agents-by-1qsn7eok1q.pdf

Scott Schaus

Papers

Aminomodified Probes for Atomic Force Microscopy

Monitoring transfected cells without selection agents by using the dual-cassette expression EGFP vectors