title: Impact of confinement on proteins concentrated in lithocholic acid based organic nanotubes.
abstract: Organic nanotubes form in aqueous solution near physiological pH by self-assembly of lithocholic acid (LCA) with inner diameters of 20-40nm. The encapsulation of enhanced green fluorescent protein (eGFP) and resultant confinement effect for eGFP within these nanotubes is studied via confocal microscopy. Timed release rate studies of eGFP encapsulated in LCA nanotubes and fluorescence recovery after photobleaching (FRAP) indicate that the diffusive transport of eGFP out of and/or within the nanotubes is very slow, in contrast to the rapid introduction of eGFP into the nanotubes. By encapsulating two fluorescent proteins in LCA nanotubes, eGFP and mCherry, as a fluorescence resonance energy transfer (FRET) pair, the FRET efficiencies are determined using FRET imaging microscopy at three different protein concentrations with a fixed donor-to-acceptor ratio of 1:1. Förster theory reveals that the proteins are spatially separated by 4.8-7.2nm in distance inside these nanotubes. The biomimetic nanochannels of LCA nanotubes not only afford a confining effect on eGFP that results in enhanced chemical and thermal stability under conditions of high denaturant concentration and temperature, but also function as protein concentrators for enriching protein in the nanochannels from a diluted protein solution by up to two orders of magnitude.
authors.affiliation: Naval Research Laboratory, Chemistry Division, Code 6112, 4555 Overlook Ave., SW, Washington, D.C. 20375-5342, USA. Electronic address: qin.lu@nrl.navy.mil.
authors.forename: Qin
authors.initials: Q
authors.lastname: Lu
authors.affiliation: Naval Research Laboratory, Center for Computational Materials Science, Code 6394, 4555 Overlook Ave., SW, Washington, D.C. 20375, USA. Electronic address: youngchan.kim@nrl.navy.mil.
authors.forename: Youngchan
authors.initials: Y
authors.lastname: Kim
authors.affiliation: Naval Research Laboratory, Materials Science and Technology Division, Code 6366, 4555 Overlook Ave., SW, Washington, D.C. 20375, USA. Electronic address: nabil.bassim@nrl.navy.mil.
authors.forename: Nabil
authors.initials: N
authors.lastname: Bassim
authors.affiliation: Naval Research Laboratory, Chemistry Division, Code 6112, 4555 Overlook Ave., SW, Washington, D.C. 20375-5342, USA. Electronic address: greg.collins@nrl.navy.mil.
authors.forename: Greg E
authors.initials: GE
authors.lastname: Collins
mesh_terms: D004058:Diffusion; D004339:Drug Compounding; D036681:Fluorescence Recovery After Photobleaching; D031541:Fluorescence Resonance Energy Transfer; D049452:Green Fluorescent Proteins / Q000737:chemistry*; D007700:Kinetics; D008095:Lithocholic Acid / Q000737:chemistry*; D008164:Luminescent Proteins / Q000737:chemistry*; D008856:Microscopy, Fluorescence; D056004:Molecular Dynamics Simulation; D043942:Nanotubes / Q000737:chemistry* / Q000648:ultrastructure; D010316:Particle Size; D055550:Protein Stability; D012996:Solutions; D013816:Thermodynamics; D014867:Water / Q000737:chemistry; D000097573:Red Fluorescent Protein
chemical_list: D049452:Green Fluorescent Proteins; D008095:Lithocholic Acid; D008164:Luminescent Proteins; D012996:Solutions; D014867:Water; D000097573:Red Fluorescent Protein; C485184:enhanced green fluorescent protein
keywords: Confocal microscopy; Lipid nanotubes; Lithocholic acid; Stability; eGFP