Biomolecular interactions and tools for their recognition: focus on the quartz crystal microbalance and its diverse surface chemistries and applications.

Interactions between molecules are ubiquitous and occur in our bodies, the food we eat, the air we breathe, and myriad additional contexts. Although numerous tools are available for the recognition of biomolecular interactions, such tools are often limited in their sensitivity, expensive, and difficult to modify for various uses. In contrast, the quartz crystal microbalance (QCM) has sub-nanogram detection capabilities, is label-free, is inexpensive to create, and can be readily modified with a number of diverse surface chemistries to detect and characterize diverse interactions. To maximize the versatility of the QCM, scientists need to know available methods by which QCM surfaces can be modified. Therefore, in addition to summarizing the various tools currently used for biomolecular recognition, explicating the fundamental principles of the QCM as a tool for biomolecular recognition, and comparing the QCM with other acoustic sensors, we systematically review the numerous types of surface chemistries-including hydrophobic bonds, ionic bonds, hydrogen bonds, self-assembled monolayers, plasma-polymerized films, photochemistry, and sensing ionic liquids-used to functionalize QCMs for various purposes. We also review the QCM's diverse applications, which include the detection of gaseous species, detection of carbohydrates, detection of nucleic acids, detection of non-enzymatic proteins, characterization of enzymatic activity, detection of antigens and antibodies, detection of cells, and detection of drugs. Finally, we discuss the ultimate goals of and potential barriers to the development of future QCMs.

Brain activity measured by functional magnetic resonance imaging is related to patient reported urgency urinary incontinence severity.

PURPOSE: We investigated the relationship between experimental neuroimaging and self-reported urinary incontinence measures. MATERIALS AND METHODS: We evaluated 14 functionally independent, community dwelling women older than 60 years with moderate to severe urgency urinary incontinence. All underwent detailed clinical assessment (3-day bladder diary, 24-hour pad test and quality of life assessment), urodynamic testing and functional brain scanning. Brain activity during reported urgency was assessed using a method that combines functional magnetic resonance imaging with simultaneous urodynamic monitoring during repeat bladder filling/emptying cycles. We used the statistical parametric mapping program SPM2 (http://www.fil.ion.ucl.ac.uk/spm/spm2.html) to correlate brain activity with relevant clinical covariates, including the number of urgency incontinent episodes, amount of urine leakage and psychological burden as assessed by the Urge Impact Scale questionnaire. RESULTS: Activity in rostral and subgenual anterior cingulate gyrus, insula, inferior frontal gyrus, orbitofrontal cortex, dorsal and posterior cingulate gyrus, parahippocampus, cuneus and parts of parietotemporal lobe correlated positively with daytime incontinence frequency and urine loss. Different brain regions correlated with the psychological burden and the associations were inverse, that is precuneus/cuneus and posterior cingulate gyrus, and superior temporal, supramarginal and transverse gyrus. CONCLUSIONS: As provoked by bladder filling, regional brain activity in the setting of self-reported urgency correlates significantly with incontinence severity in daily life and the associated psychological burden. Thus, observations made under experimental conditions correlate with patient real-life experience and suggest neural correlates of urgency incontinence symptoms that could serve as potential targets for future investigations.

Distinct pharmacological effects of inhibitors of signal peptide peptidase and gamma-secretase.

Signal peptide peptidase (SPP) and gamma-secretase are intramembrane aspartyl proteases that bear similar active site motifs but with opposite membrane topologies. Both proteases are inhibited by the same aspartyl protease transition-state analogue inhibitors, further evidence that these two enzymes have the same basic cleavage mechanism. Here we report that helical peptide inhibitors designed to mimic SPP substrates and interact with the SPP initial substrate-binding site (the "docking site") inhibit both SPP and gamma-secretase, but with submicromolar potency for SPP. SPP was labeled by helical peptide and transition-state analogue affinity probes but at distinct sites. Nonsteroidal anti-inflammatory drugs, which shift the site of proteolysis by SPP and gamma-secretase, did not affect the labeling of SPP or gamma-secretase by the helical peptide or transition-state analogue probes. On the other hand, another class of previously reported gamma-secretase modulators, naphthyl ketones, inhibited SPP activity as well as selective proteolysis by gamma-secretase. These naphthyl ketones significantly disrupted labeling of SPP by the helical peptide probe but did not block labeling of SPP by the transition-state analogue probe. With respect to gamma-secretase, the naphthyl ketone modulators allowed labeling by the transition-state analogue probe but not the helical peptide probe. Thus, the naphthyl ketones appear to alter the docking sites of both SPP and gamma-secretase. These results indicate that pharmacological effects of the four different classes of inhibitors (transition-state analogues, helical peptides, nonsteroidal anti-inflammatory drugs, and naphthyl ketones) are distinct from each other, and they reveal similarities and differences with how they affect SPP and gamma-secretase.