NAD binding by human CD38 analyzed by Trp189 fluorescence

Combination of RT-LAMP and fluorescence spectroscopy using chemometric techniques for an ultra-sensitive and rapid alternative for the detection of SARS-CoV-2

The increased spread of COVID-19 caused by SARS-CoV-2 has made it necessary to develop more efficient, fast, accurate, specific, sensitive and easy-to-use detection platforms to overcome the disadvantages of gold standard methods (RT-qPCR). Here an approach was developed for the detection of the SARS-CoV-2 virus using the loop-mediated isothermal amplification (LAMP) technique for SARS-CoV-2 RNA target amplification in samples of nasopharyngeal swabs. The discrimination between positive and negative SARS-CoV-2 samples was achieved by using fluorescence spectra generated by the excitation of the LAMP's DNA intercalator dye at λ497 nm in a fluorescence spectrophotometer and chemometric tools. Exploratory analysis of the 83 sample spectra using principal component analysis (PCA) indicated a trend in differentiation between positive and negative samples resulting from the peak emission of the fluorescent dye. The classification was performed by partial least squares discriminant analysis (PLS-DA) achieving a sensitivity, a specificity and an accuracy of 100%, 95% and 89%, respectively for the discrimination between negative and positive samples from 1.58 to 0.25 ng L^-1 after LAMP amplification. Therefore, this study indicates that the use of the LAMP technique in fluorescence spectroscopy may offer a fast (<1 hour), sensitive and low-cost method.

Inhibition of epithelial phosphate transport by NAD+/NADH

Nicotinamide is an important regulator of Pi homeostasis after conversion into NAD⁺/NADH. In this work, we have studied the classical inhibition of Pi transport by these compounds in the brush border membrane vesicles (BBMV) of rat kidney and rat intestine, and we examined the effects in Opossum Kidney (OK) cells and in phosphate transporter-expressing Xenopus laevis oocytes. In BBMV, NAD⁺ required preincubation at either room temperature or on ice to inhibit Pi uptake in BBMV. However, no effects were observed in the known Slc34 or Slc20 Pi transporters expressed in Xenopus oocytes, in OK cells, or in isolated rat cortical nephron segments. In BBMV from jejunum or kidney cortex, the inhibition of Pi transport was specific, dose-related, and followed a competitive inhibition pattern, as shown by linear transformation and non-linear regression analyses. A K_i value of 538 µM NAD⁺ in kidney BBMV was obtained. Ribosylation inhibitors and ribosylation assays revealed no evidence that this reaction was responsible for inhibiting Pi transport. An analysis of the persistence of NAD⁺/NADH revealed a half-life of just 2 minutes during preincubation. Out of several metabolites of NAD degradation, only ADP-ribose was able to inhibit Pi uptake. Pi concentration also increased during 30 minutes of preincubation, up to 0.67mM, most likely as a metabolic end-product. In conclusion, the classical inhibition of Pi transport by NAD⁺/NADH in BBMV seems to be caused by the degradation metabolites of these compounds during the preincubation time.

HN1L/JPT2: A signaling protein that connects NAADP generation to Ca2+ microdomain formation

NAADP-evoked Ca²⁺ release through type 1 ryanodine receptors (RYR1) is a major mechanism underlying the earliest signals in T cell activation, which are the formation of Ca²⁺ microdomains. In our characterization of the molecular machinery underlying NAADP action, we identified an NAADP-binding protein, called hematological and neurological expressed 1-like protein (HN1L) [also known as Jupiter microtubule-associated homolog 2 (JPT2)]. Gene deletion of Hn1l/Jpt2 in human Jurkat and primary rat T cells resulted in decreased numbers of initial Ca²⁺ microdomains and delayed the onset and decreased the amplitude of global Ca²⁺ signaling. Photoaffinity labeling demonstrated direct binding of NAADP to recombinant HN1L/JPT2. T cell receptor/CD3-dependent coprecipitation of HN1L/JPT2 with RYRs and colocalization of these proteins suggest that HN1L/JPT2 connects NAADP formation with the activation of RYR channels within the first seconds of T cell activation. Thus, HN1L/JPT2 enables NAADP to activate Ca²⁺ release from the endoplasmic reticulum through RYR.