title: Characterization of lithium coordination sites with magic-angle spinning NMR.
abstract: Lithium, in the form of lithium carbonate, is one of the most common drugs for bipolar disorder. Lithium is also considered to have an effect on many other cellular processes hence it possesses additional therapeutic as well as side effects. In order to quantitatively characterize the binding mode of lithium, it is required to identify the interacting species and measure their distances from the metal center. Here we use magic-angle spinning (MAS) solid-state NMR to study the binding site of lithium in complex with glycine and water (LiGlyW). Such a compound is a good enzyme mimetic since lithium is four-coordinated to one water molecule and three carboxylic groups. Distance measurements to carbons are performed using a 2D transferred echo double resonance (TEDOR) MAS solid-state NMR experiment, and water binding is probed by heteronuclear high-resolution proton-lithium and proton-carbon correlation (wPMLG-HETCOR) experiments. Both HETCOR experiments separate the main complex from impurities and non-specifically bound lithium species, demonstrating the sensitivity of the method to probe the species in the binding site. Optimizations of the TEDOR pulse scheme in the case of a quadrupolar nucleus with a small quadrupole coupling constant show that it is most efficient when pulses are positioned on the spin-1/2 (carbon-13) nucleus. Since the intensity of the TEDOR signal is not normalized, careful data analysis that considers both intensity and dipolar oscillations has to be performed. Nevertheless we show that accurate distances can be extracted for both carbons of the bound glycine and that these distances are consistent with the X-ray data and with lithium in a tetrahedral environment. The lithium environment in the complex is very similar to the binding site in inositol monophosphatase, an enzyme associated with bipolar disorder and the putative target for lithium therapy. A 2D TEDOR experiment applied to the bacterial SuhB gene product of this enzyme was designed to probe direct correlations between lithium, the enzyme inhibitor, and the closest carboxyl carbons of the binding site. At this point, the chemical shift of the bound carboxyl groups in this 29 kDa enzyme could be determined.
authors.affiliation: School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv 69978, Tel Aviv, Israel.
authors.forename: A
authors.initials: A
authors.lastname: Haimovich
authors.affiliation: School of Chemistry, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Ramat Aviv 69978, Tel Aviv, Israel. Electronic address: amirgo@post.tau.ac.il.
authors.forename: A
authors.initials: A
authors.lastname: Goldbourt
mesh_terms: D000465:Algorithms; D001419:Bacteria / Q000201:enzymology; D001665:Binding Sites; D003198:Computer Simulation; D005998:Glycine / Q000737:chemistry; D008094:Lithium / Q000737:chemistry*; D016651:Lithium Carbonate / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D010744:Phosphoric Monoester Hydrolases / Q000737:chemistry; D011522:Protons; D011846:Radio Waves; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D011522:Protons; D014867:Water; D016651:Lithium Carbonate; D008094:Lithium; D010744:Phosphoric Monoester Hydrolases; C021822:myo-inositol-1 (or 4)-monophosphatase; D005998:Glycine
keywords: HETCOR; Lithium; Magic angle spinning; Metal coordination site; PMLG; Solid-state NMR; TEDOR