Binding of muscimol-conjugated quantum dots to GABAC receptors.
Functionalization of highly fluorescent CdSe/ZnS core-shell nanocrystals (quantum dots, qdots) is an emerging technology for labeling cell surface proteins. We have synthesized a conjugate consisting of approximately 150-200 muscimols (a GABA receptor agonist) covalently joined to the qdot via a poly(ethylene glycol) (PEG) linker (approximately 78 ethylene glycol units) and investigated the binding of this muscimol-PEG-qdot conjugate to homomeric rho1 GABAC receptors expressed in Xenopus oocytes. GABAC receptors mediate inhibitory synaptic signaling at multiple locations in the central nervous system (CNS). Binding of the conjugate was analyzed quantitatively by determining the fluorescence intensity of the oocyte surface membrane in relation to that of the surrounding incubation medium. Upon 5- to 10-min incubation with muscimol-PEG-qdots (34 nM in qdot concentration), GABAC-expressing oocytes exhibited a fluorescent halo at the surface membrane that significantly exceeded the fluorescence of the incubation medium. This halo was absent following muscimol-PEG-qdot treatment of oocytes lacking GABAC receptors. Incubation of the oocyte with free muscimol (100 microM-5 mM), PEG-muscimol (500 microM), or GABA (100 microM - 5 mM) substantially reduced or eliminated the fluorescence halo produced by muscimol-PEG-qdots, and the removal of GABA or free muscimol led to a recovery of muscimol-PEG-qdot binding. Unconjugated qdots and PEG-qdots that lacked conjugated muscimol neither exhibited significant binding activity nor diminished the subsequent binding of muscimol-PEG-qdots. The results indicate that muscimol joined to qdots via a long-chain PEG linker exhibits specific binding activity at the ligand-binding pocket of expressed GABAC receptors, despite the presence of both the long PEG linker and the sterically bulky qdot.
PubMed ID: 17147380
PMC ID: PMC2553244
Article link: J Am Chem Soc.
Grant support: EB003728 NIBIB NIH HHS , EY01792 NEI NIH HHS , EY019094 NEI NIH HHS , EY05494 NEI NIH HHS , EY13693 NEI NIH HHS , MH075791 NIMH NIH HHS, P20 GM072048-01 NIGMS NIH HHS , P20 GM072048-02 NIGMS NIH HHS , P20 GM072048-03 NIGMS NIH HHS , P30 EY001792-26 NEI NIH HHS , P30 EY001792-27 NEI NIH HHS , P30 EY001792-28 NEI NIH HHS , R01 EB003728-01 NIBIB NIH HHS , R01 EB003728-02 NIBIB NIH HHS , R01 EB003728-03 NIBIB NIH HHS , R01 EY005494-20 NEI NIH HHS , R01 EY005494-21 NEI NIH HHS , R01 EY005494-22 NEI NIH HHS , R01 EY016094-01A1 NEI NIH HHS , R03 EY013693-02 NEI NIH HHS , R03 EY013693-03 NEI NIH HHS , R03 EY013693-03S1 NEI NIH HHS , R03 MH075791-01 NIMH NIH HHS, P20 GM072048 NIGMS NIH HHS , R01 EB003728 NIBIB NIH HHS , R01 EY005494 NEI NIH HHS , R01 EY016094 NEI NIH HHS , R03 EY013693 NEI NIH HHS , R03 MH075791 NIMH NIH HHS