Innate and adaptive defense mechanisms protect the respiratory system from attack by microbes. Here, we present evidence that the bitter taste receptor T2R38 regulates the mucosal innate defense of the human upper airway. Utilizing immunofluorescent and live cell imaging techniques in polarized primary human sinonasal cells, we demonstrate that T2R38 is expressed in human upper respiratory epithelium and is activated in response to acyl-homoserine lactone quorum-sensing molecules secreted by Pseudomonas aeruginosa and other gram-negative bacteria. Receptor activation regulates calcium-dependent NO production, resulting in stimulation of mucociliary clearance and direct antibacterial effects. Moreover, common polymorphisms of the TAS2R38 gene were linked to significant differences in the ability of upper respiratory cells to clear and kill bacteria. Lastly, TAS2R38 genotype correlated with human sinonasal gram-negative bacterial infection. These data suggest that T2R38 is an upper airway sentinel in innate defense and that genetic variation contributes to individual differences in susceptibility to respiratory infection.

Background—: Inorganic nitrate (NO ₃ ⁻ ), abundant in certain vegetables, is converted to nitrite by bacteria in the oral cavity. Nitrite can be converted to nitric oxide in the setting of hypoxia. We tested the hypothesis that NO ₃ ⁻ supplementation improves exercise capacity in heart failure with preserved ejection fraction via specific adaptations to exercise. Methods and Results—: Seventeen subjects participated in this randomized, double-blind, crossover study comparing a single dose of NO ₃ -rich beetroot juice (NO ₃ ⁻ , 12.9 mmol) with an identical nitrate-depleted placebo. Subjects performed supine-cycle maximal-effort cardiopulmonary exercise tests, with measurements of cardiac output and skeletal muscle oxygenation. We also assessed skeletal muscle oxidative function. Study end points included exercise efficiency (total work/total oxygen consumed), peak o ₂ , total work performed, vasodilatory reserve, forearm mitochondrial oxidative function, and augmentation index (a marker of arterial wave reflections, measured via radial arterial tonometry). Supplementation increased plasma nitric oxide metabolites (median, 326 versus 10 μmol/L; P =0.0003), peak o ₂ (12.6±3.7 versus 11.6±3.1 mL O ₂ ·min ⁻¹ ·kg ⁻¹ ; P =0.005), and total work performed (55.6±35.3 versus 49.2±28.9 kJ; P =0.04). However, efficiency was unchanged. NO ₃ ⁻ led to greater reductions in systemic vascular resistance (−42.4±16.6% versus −31.8±20.3%; P =0.03) and increases in cardiac output (121.2±59.9% versus 88.7±53.3%; P =0.006) with exercise. NO ₃ ⁻ reduced aortic augmentation index (132.2±16.7% versus 141.4±21.9%; P =0.03) and tended to improve mitochondrial oxidative function. Conclusions—: NO ₃ ⁻ increased exercise capacity in heart failure with preserved ejection fraction by targeting peripheral abnormalities. Efficiency did not change as a result of parallel increases in total work and o _2. NO ₃ ⁻ increased exercise vasodilatory and cardiac output reserves. NO ₃ ⁻ also reduced arterial wave reflections, which are linked to left ventricular diastolic dysfunction and remodeling. Clinical Trial Registration—: URL: www.clinicaltrials.gov . Unique identifier: NCT01919177.

NO is a versatile free radical that mediates numerous biological functions within every major organ system. A molecular pathway by which NO accomplishes functional diversity is the selective modification of protein cysteine residues to form S-nitrosocysteine. This post-translational modification, S-nitrosylation, impacts protein function, stability, and location. Despite considerable advances with individual proteins, the in vivo biological chemistry, the structural elements that govern the selective S-nitrosylation of cysteine residues, and the potential overlap with other redox modifications are unknown. In this minireview, we explore the functional features of S-nitrosylation at the proteome level and the structural diversity of endogenously modified residues, and we discuss the potential overlap and complementation that may exist with other cysteine modifications.

S -nitrosylation increases the catalytic efficiency of an enzyme critical to fatty acid β-oxidation.

S-nitrosylation, the selective posttranslational modification of protein cysteine residues to form S-nitrosocysteine, is one of the molecular mechanisms by which nitric oxide influences diverse biological functions. In this study, unique MS-based proteomic approaches precisely pinpointed the site of S-nitrosylation in 328 peptides in 192 proteins endogenously modified in WT mouse liver. Structural analyses revealed that S-nitrosylated cysteine residues were equally distributed in hydrophobic and hydrophilic areas of proteins with an average predicted pK _a of 10.01 ± 2.1. S-nitrosylation sites were over-represented in α-helices and under-represented in coils as compared with unmodified cysteine residues in the same proteins (χ ² test, P < 0.02). A quantile–quantile probability plot indicated that the distribution of S-nitrosocysteine residues was skewed toward larger surface accessible areas compared with the unmodified cysteine residues in the same proteins. Seventy percent of the S-nitrosylated cysteine residues were surrounded by negatively or positively charged amino acids within a 6-Å distance. The location of cysteine residues in α-helices and coils in highly accessible surfaces bordered by charged amino acids implies site directed S-nitrosylation mediated by protein–protein or small molecule interactions. Moreover, 13 modified cysteine residues were coordinated with metals and 15 metalloproteins were endogenously modified supporting metal-catalyzed S-nitrosylation mechanisms. Collectively, the endogenous S-nitrosoproteome in the liver has structural features that accommodate multiple mechanisms for selective site-directed S-nitrosylation.