The Bitter Taste Receptor TAS2R16 Achieves High Specificity and Accommodates Diverse Glycoside Ligands by using a Two-faced Binding Pocket.

Although bitter taste receptors (TAS2Rs) are important for human health, little is known of the determinants of ligand specificity. TAS2Rs such as TAS2R16 help define gustatory perception and dietary preferences that ultimately influence human health and disease. Each TAS2R must accommodate a broad diversity of chemical structures while simultaneously achieving high specificity so that diverse bitter toxins can be detected without all foods tasting bitter. However, how these G protein-coupled receptors achieve this balance is poorly understood. Here we used a comprehensive mutation library of human TAS2R16 to map its interactions with existing and novel agonists. We identified 13 TAS2R16 residues that contribute to ligand specificity and 38 residues whose mutation eliminated signal transduction by all ligands, providing a comprehensive assessment of how this GPCR binds and signals. Our data suggest a model in which hydrophobic residues on TM3 and TM7 form a broad ligand-binding pocket that can accommodate the diverse structural features of ß-glycoside ligands while still achieving high specificity.

Ultrasonographic Diagnosis of Intrauterine Fetal Decapitation Secondary to Amniotic Band Sequence: A Case Report.

BACKGROUND: Amniotic band sequence (ABS) is a rare disorder that can result in a wide spectrum of congenital craniofacial, limb, trunk, and viscera deformities. One of the more rare manifestations of ABS is intrauterine fetal decapitation. CASE REPORT: This case report presents the ultrasonographic diagnosis of first-trimester intrauterine fetal demise resulting from decapitation secondary to amniotic band sequence. WHY SHOULD AN EMERGENCY PHYSICIAN BE AWARE OF THIS?: This case report presents a rare and atypical presentation of intrauterine demise valuable for an emergency physician to recognize while performing or reviewing pelvic ultrasounds. It is important for the clinician to understand and counsel the patient that subsequent pregnancies will not be at increased risk due to a prior miscarriage from ABS, as opposed to other etiologies of first-trimester spontaneous abortion.