Arfaan Rampersaud

The Tar chemoreceptor of Escherichia coli is a membrane-bound sensory protein that facilitates bacterial chemotaxis in response to aspartate. The EnvZ molecule has a membrane topology similar to Tar and is a putative osmosensor that is required for osmoregulation of the genes for the major outer membrane porin proteins, OmpF and OmpC. The cytoplasmic signaling domain of Tar was replaced with the carboxyl portion of EnvZ, and the resulting chimeric receptor activated transcription of the ompC gene in response to aspartate. The activation of ompC by the chimeric receptor was absolutely dependent on OmpR, a transcriptional activator for ompF and ompC.

Abstract Multi‐color fluorescent nanodiamonds (FNDs) containing a variety of color centers are promising fluorescent markers for biomedical applications. Compared to colloidal quantum dots and organic dyes, FNDs have the advantage of lower toxicity, exceptional chemical stability, and better photostability. They can be surface functionalized by techniques similar to those used for other nanoparticles. They exhibit a variety of emission wavelengths from visible to near infrared, with narrow or broad bandwidths depending on their color centers. In addition, some color centers can detect changes in magnetic fields, electric fields, and temperature. In this article review, we will discuss the current trends in FND’s development, including comparison to the early development of quantum dots. We will also highlight some of the latest advances in fabrication, as well as demonstrations of their use in bioimaging and biosensing.

Glycosphingolipids are amphipathic compounds that exist mainly in the plasmalemma with their oligosaccharide portion protruding into the extracellular environment. In this position they are admirably situated for interacting with both ligands and receptors. Binding studies have demonstrated that specific glycolipids function as receptors for some microorganisms and bacterial toxins. Specific oligosaccharides on both glycolipids and glycoproteins bind members of the selection families, and some gangliosides facilitate integrins binding to their ligands. Gangliosides modulate the trophic factor-stimulated dimerization, tyrosine phosphorylation, and subsequent signal transduction events of several tyrosine kinase receptors. GM3 inhibits both the epidermal growth factor receptor and basic fibroblast factor receptor; several gangliosides except GM3 inhibit the platelet-derived growth-factor receptor; GM1 enhances nerve growth-factor-stimulated activation of TrkA; insulin receptor is inhibited to varying degrees by several gangliosides, but 2-->3 sialosylparagloboside is most effective. Activities of the beta(1)-adrenergic and delta-opioid receptors are modulated by GM1. Available information suggests that glycolipids serve as coordinators of multiple receptor functions.

In Escherichia coli the ompF gene encodes a major outer membrane porin protein that is differentially regulated by the OmpR protein. OmpR acts as a positive as well as a negative regulator of ompF expression by binding to DNA sequences in the ompF promoter region. The DNA binding activity of OmpR is itself regulated by phosphorylation through the kinase protein EnvZ. Phosphorylation is believed to change the function of OmpR from an activator to a repressor molecule. By using purified OmpR and various regions of the ompF promoter we show that phosphorylation causes binding of OmpR to a DNA region between the -40 to -100 region of the ompF promoter previously shown to be important for ompF expression. As the amount of OmpR-phosphate increases, a binding site located at a further upstream -360 to -380 region was occupied. This latter site has been reported to be important for ompF repression. Further experiments indicate that the -70 to -100 region is a high affinity site, while the -45 to -60 and -360 to -380 regions are low affinity sites. We also provide evidence that OmpR binding at the -360 to -380 region requires previous binding at downstream sequences, which is indicative of long range interactions between OmpR molecules. We interpret our results in terms of a model for ompF regulation involving hierarchical binding by phosphorylated OmpR and potential DNA looping.