Bispidine as a Versatile Scaffold: From Topological Hosts to Transmembrane Transporters.

The development of designer topological structures is a synthetically challenging endeavor. We present herein bispidine as a platform for the design of molecules with various topologies and functions. The bispidine-based acyclic molecule, which shows intriguing S-shape topology, is discussed. Single-crystal X-ray diffraction studies revealed that this molecule exists in the solid state as two conformational enantiomers. In addition, bispidine-based designer macrocycles were synthesized and investigated for ionophoric properties. Patch clamp experiments revealed that these macrocycles transport both anions and cations non-specifically with at least tenfold higher chloride conductance over the cations under the given experimental conditions. Ultramicroscopy and single-crystal X-ray crystallographic studies indicated that the self-assembling macrocycle forms a tubular assembly. Our design highlights the use of unconventional dihydrogen interactions in nanotube fabrication.

Protein engineering and design in ion channels and receptors.

Acetylcholine receptors (AChRs) expressed at the neuromuscular junction synapses are typical allosteric proteins that shuttle between at least two stable conformational states: Closed (C) and Open (O). Agonist binding to their target sites on the receptor in the extracellular domain triggers a global C→O conformational change that results in an open channel pore that allows ion conduction. How the receptor senses the chemical signal of an agonist and communicates it to the channel pore, located ~50Šaway, are key to understanding the receptor function. AChRs are indispensable for muscle contraction and their neuronal homologues play critical roles in the nervous system function. In this chapter, using a combination of single channel patch-clamp, computational approaches, and genetic engineering, we elucidate the principles of design and engineering to quantify the fundamental thermodynamic parameters of AChRs that regulate ligand binding and channel opening. The receptor engineering principles outlined here for the neuromuscular AChRs are applicable to the broader class of ligand-gated ion channel proteins.