Programming A Molecular Relay for Ultrasensitive Biodetection through ¹²⁹Xe NMR

Abstract

Here, we report a supramolecular strategy for detecting specific proteins in complex media using hyperpolarized 129Xe NMR. A cucurbit[6]uril (CB[6]) based molecular relay was programmed for three sequential equilibrium conditions by designing a two-faced guest (TFG) that initially binds CB[6] and blocks CB[6]-Xe interaction. Protein analyte recruits the TFG and frees CB[6] for Xe binding. TFGs containing CB[6]- and carbonic anhydrase II (CAII)-binding domains were synthesized in one or two steps. X-ray crystallography confirmed TFG binding to Zn2+ in the deep, active-site CAII cleft, which precludes simultaneous CB[6] binding. The molecular relay was reprogrammed to detect avidin using a different TFG. Finally, CB[6]-Xe binding was detected in buffer and in E. coli cultures expressing CAII via ultrasensitive 129Xe NMR spectroscopy.

Xenon–Protein Interactions: Characterization by X-Ray Crystallography and Hyper-CEST NMR

“…Depolarized Xe rapidly exchanges into solvent, depolarizing the reservoir of bulk Xe which, in turn, generates MR contrast. Our lab has employed hyper-CEST to study Xe interactions with spores (Bai et al, 2014) as well as the proteins TEM-1 β-lactamase (Bla) (Wang et al, 2016) and maltose binding protein (MBP) (Roose, Zemerov, & Dmochowski, 2017). Representative hyper-CEST z-spectra for 80 μM Bla and MBP in PBS are shown in Fig.…”

Protein Nanostructures Produce Self-Adjusting Hyperpolarized Magnetic Resonance Imaging Contrast through Physical Gas Partitioning

“…The solution is a system of exchange-coupled spin pools where both pools grow proportionately to keep their size ratio, f B , and, thus, the CEST efficiency constant. This approach is conceptually different from 1:1 Xe complex formation, protein-based sensors 18,19 or reversible chemical binding in 1 H CEST. We demonstrate ideal CEST performance through simple physical partitioning of a dissolved gas into a nano-sized volume ( Figure 1B), thereby introducing the concept of an "elastic" contrast agent for Hyper-CEST.…”

A Genetically Encoded β‐Lactamase Reporter for Ultrasensitive 129Xe NMR in Mammalian Cells

“…[3] HP 129 Xe is non-toxic, can be delivered to living organisms via inhalation or Xe-solution injection, and has been employed for imaging the lungs and brain of living mammals, including human. [4] Xenon has high affinity for hydrophobic void spaces, including host molecules such as water-soluble cryptophane and cucurbituril, [5] and the highly polarizable electron cloud affords xenon high sensivitiy to its local environment. The interactions between xenon and small molecules have led to many biosensing applications.…”