Reprogramming cellular functions with engineered membrane proteins.

Taking inspiration from Nature, synthetic biology utilizes and modifies biological components to expand the range of biological functions for engineering new practical devices and therapeutics. While early breakthroughs mainly concerned the design of gene circuits, recent efforts have focused on engineering signaling pathways to reprogram cellular functions. Since signal transduction across cell membranes initiates and controls intracellular signaling, membrane receptors have been targeted by diverse protein engineering approaches despite limited mechanistic understanding of their function. The modular architecture of several receptor families has enabled the empirical construction of chimeric receptors combining domains from distinct native receptors which have found successful immunotherapeutic applications. Meanwhile, progress in membrane protein structure determination, computational modeling and rational design promise to foster the engineering of a broader range of membrane receptor functions. Marrying empirical and rational membrane protein engineering approaches should enable the reprogramming of cells with widely diverse fine-tuned functions.

Computational design of ligand-binding membrane receptors with high selectivity.

Accurate modeling and design of protein-ligand interactions have broad applications in cell biology, synthetic biology and drug discovery but remain challenging without experimental protein structures. Here we developed an integrated protein-homology-modeling, ligand-docking protein-design approach that reconstructs protein-ligand binding sites from homolog protein structures in the presence of protein-bound ligand poses to capture conformational selection and induced-fit modes of ligand binding. In structure modeling tests, we blindly predicted, with near-atomic accuracy, ligand conformations bound to G-protein-coupled receptors (GPCRs) that have rarely been identified using traditional approaches. We also quantitatively predicted the binding selectivity of diverse ligands to structurally uncharacterized GPCRs. We then applied this technique to design functional human dopamine receptors with novel ligand-binding selectivity. Most blindly predicted ligand-binding specificities closely agreed with experimental validations. Our method should prove useful in ligand discovery approaches and in reprogramming the ligand-binding profile of membrane receptors that remain difficult to crystallize.

A low concentration of ethanol impairs learning but not motor and sensory behavior in Drosophila larvae.

Drosophila melanogaster has proven to be a useful model system for the genetic analysis of ethanol-associated behaviors. However, past studies have focused on the response of the adult fly to large, and often sedating, doses of ethanol. The pharmacological effects of low and moderate quantities of ethanol have remained understudied. In this study, we tested the acute effects of low doses of ethanol (∼7 mM internal concentration) on Drosophila larvae. While ethanol did not affect locomotion or the response to an odorant, we observed that ethanol impaired associative olfactory learning when the heat shock unconditioned stimulus (US) intensity was low but not when the heat shock US intensity was high. We determined that the reduction in learning at low US intensity was not a result of ethanol anesthesia since ethanol-treated larvae responded to the heat shock in the same manner as untreated animals. Instead, low doses of ethanol likely impair the neuronal plasticity that underlies olfactory associative learning. This impairment in learning was reversible indicating that exposure to low doses of ethanol does not leave any long lasting behavioral or physiological effects.

Multiple congenital genitourinary anomalies in a polled goat.

A 1-day-old, Toggenburg/Nubian crossbred goat of polled parentage was referred for necropsy because of a large (diameter, 5 cm) bladder-like mass protruding from the perineal midline and difficult urination. Differential diagnoses included cutaneous cyst, ectopic urinary bladder, and urethral diverticulum/dilatation. Several genitourinary aberrations were noted. A second, smaller (diameter, 1 cm), more distal cystic structure was adjacent to an ambiguous prepuce. Testicles were discovered within a constricted, subcutaneous space near the inguinal canals. A rudimentary penis was located dorsal to the penile urethra with no appreciable urethral process. A tiny external urethral orifice was discerned only after liquid was injected into the lumen of the cystic structures, confirming their identity as urethral dilatations. The dilatations were separated by a constricting band of fibrous tissue. No other significant findings were detected. This case illustrates a combination of congenital anomalies including bilateral cryptorchidism with scrotal absence, segmental urethral hypoplasia, and urethral dilatation, most likely associated with the intersex condition seen in polled breeds. The continued production and use of small ruminants as animal models demands the prompt recognition of congenital anomalies. This case also exemplifies the precautions required when breeding goats with polled ancestry.