[show abstract][hide abstract] ABSTRACT: The evolution of a total synthesis of the exiguamines, two structurally unusual natural products that are highly active inhibitors of indolamine-2,3-dioxygenase (IDO), is described. The ultimately successful strategy involves advanced cross-coupling methodology and features a potentially biosynthetic tautomerization/electrocyclization cascade reaction that forms two heterocycles and installs a quaternary ammonium ion in a single synthetic operation.
[show abstract][hide abstract] ABSTRACT: Photoswitched tethered ligands (PTLs) can be used to remotely control protein function with light. We have studied the geometric and conformational factors that determine the efficacy of PTL gating in the ionotropic glutamate receptor iGluR6 using a family of photoiosomerizable MAG (maleimide-azobenzene-glutamate) PTLs that covalently attach to the clamshell ligand-binding domain. Experiments and molecular dynamics simulations of the modified proteins show that optical switching depends on 2 factors: (i) the relative occupancy of the binding pocket in the 2 photoisomers of MAG and (ii) the degree of clamshell closure that is possible given the disposition of the MAG linker. A synthesized short version of MAG turns the channel on in either the cis or trans state, depending on the point of attachment. This yin/yang optical control makes it possible for 1 wavelength of light to elicit action potentials in one set of neurons, while deexciting a second set of neurons in the same preparation, whereas a second wavelength has the opposite effect. The ability to generate opposite responses with a single PTL and 2 versions of a target channel, which can be expressed in different cell types, paves the way for engineering opponency in neurons that mediate opposing functions.
Proceedings of the National Academy of Sciences 05/2009; 106(16):6814-9. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Biomimetic synthesis is an attempt to assemble natural products along biosynthetic lines without recourse to the full enzymatic machinery of nature. We exemplify this with a total synthesis of exiguamine A and the newly isolated natural product exiguamine B. The most noteworthy feature of this work is an oxidative endgame drawing from the complex chemistry of catecholamines, which allows for ready access to a new class of nanomolar indoleamine-2,3-dioxygenase inhibitors.
Nature Chemical Biology 10/2008; 4(9):535-7. · 12.95 Impact Factor
[show abstract][hide abstract] ABSTRACT: A key technical barrier to furthering our understanding of complex neural networks has been the lack of tools for the simultaneous spatiotemporal control and detection of activity in a large number of neurons. Here, we report an all-optical system for achieving this kind of parallel and selective control and detection. We do this by delivering spatiotemporally complex optical stimuli through a digital micromirror spatiotemporal light modulator to cells expressing the light-activated ionotropic glutamate receptor (LiGluR), which have been labeled with a calcium dye to provide a fluorescent report of activity. Reliable and accurate spatiotemporal stimulation was obtained on HEK293 cells and cultured rat hippocampal neurons. This technique should be adaptable to in vivo applications and could serve as an optical interface for communicating with complex neural circuits.
[show abstract][hide abstract] ABSTRACT: The analysis of cell signaling requires the rapid and selective manipulation of protein function. We have synthesized photoswitches that covalently modify target proteins and reversibly present and withdraw a ligand from its binding site due to photoisomerization of an azobenzene linker. We describe here the properties of a glutamate photoswitch that controls an ion channel in cells. Affinity labeling and geometric constraints ensure that the photoswitch controls only the targeted channel, and enables spatial patterns of light to favor labeling in one location over another. Photoswitching to the activating state places a tethered glutamate at a high (millimolar) effective local concentration near the binding site. The fraction of active channels can be set in an analog manner by altering the photostationary state with different wavelengths. The bistable photoswitch can be turned on with millisecond-long pulses at one wavelength, remain on in the dark for minutes, and turned off with millisecond long pulses at the other wavelength, yielding sustained activation with minimal irradiation. The system provides rapid, reversible remote control of protein function that is selective without orthogonal chemistry.
Proceedings of the National Academy of Sciences 07/2007; 104(26):10865-70. · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ability to stimulate select neurons in isolated tissue and in living animals is important for investigating their role in circuits and behavior. We show that the engineered light-gated ionotropic glutamate receptor (LiGluR), when introduced into neurons, enables remote control of their activity. Trains of action potentials are optimally evoked and extinguished by 380 nm and 500 nm light, respectively, while intermediate wavelengths provide graded control over the amplitude of depolarization. Light pulses of 1-5 ms in duration at approximately 380 nm trigger precisely timed action potentials and EPSP-like responses or can evoke sustained depolarizations that persist for minutes in the dark until extinguished by a short pulse of approximately 500 nm light. When introduced into sensory neurons in zebrafish larvae, activation of LiGluR reversibly blocks the escape response to touch. Our studies show that LiGluR provides robust control over neuronal activity, enabling the dissection and manipulation of neural circuitry in vivo.
[show abstract][hide abstract] ABSTRACT: Ion channels are gated by a variety of stimuli, including ligands, voltage, membrane tension, temperature, and even light. Natural gates can be altered and augmented using synthetic chemistry and molecular biology to develop channels with completely new functional properties. Light-sensitive channels are particularly attractive because optical manipulation offers a high degree of spatial and temporal control. Over the last few decades, several channels have been successfully rendered responsive to light, including the nicotinic acetylcholine receptor, gramicidin A, a voltage-gated potassium channel, an ionotropic glutamate receptor, alpha-hemolysin, and a mechanosensitive channel. Very recently, naturally occurring light-gated cation channels have been discovered. This review covers the molecular principles that guide the engineering of light-gated ion channels for applications in biology and medicine.
[show abstract][hide abstract] ABSTRACT: The precise regulation of protein activity is fundamental to life. The allosteric control of an active site by a remote regulatory binding site is a mechanism of regulation found across protein classes, from enzymes to motors to signaling proteins. We describe a general approach for manipulating allosteric control using synthetic optical switches. Our strategy is exemplified by a ligand-gated ion channel of central importance in neuroscience, the ionotropic glutamate receptor (iGluR). Using structure-based design, we have modified its ubiquitous clamshell-type ligand-binding domain to develop a light-activated channel, which we call LiGluR. An agonist is covalently tethered to the protein through an azobenzene moiety, which functions as the optical switch. The agonist is reversibly presented to the binding site upon photoisomerization, initiating clamshell domain closure and concomitant channel gating. Photoswitching occurs on a millisecond timescale, with channel conductances that reflect the photostationary state of the azobenzene at a given wavelength. Our device has potential uses not only in biology but also in bioelectronics and nanotechnology.
Nature Chemical Biology 02/2006; 2(1):47-52. · 12.95 Impact Factor