Binding and two-dimensional crystallization of streptavidin at the air/water interface via engineered Cu-IDA chelator lipids

Synergetic gating of metal-latching ligands and metal-chelating proteins for mesoporous silica nanovehicles to enhance delivery efficiency

Stimuli-responsive drug delivery systems are highly desirable for improved therapeutic efficacy and minimized adverse effects of drugs. Mesoporous silica nanoparticles (MSNs) functionalized with pentadentate ligands, N-(3-trimethoxysilylpropyl)ethylenediamine triacetate (TSP-DATA), in the presence of metal ions with and without myoglobin (Mb)-containing surface-accessible histidine residues, were constructed for pH-triggered controlled release. The DATA ligands immobilized on the MSN pore outlets could encapsulate cargo within the pores by metal latching across pore openings, and release efficiency increased with the increase of surface density of the DATA ligands. The release efficiencies for the metal-chelating protein nanogates, through multiple-site binding of Mb with the metal-chelating ligands, were higher than those for the metal-latching ligand nanogates but were almost independent of surface density of the ligands investigated. Both the metal-latching ligands and the metal-chelating proteins played a synergetic role in gating MSNs for high-loading drug delivery and stimuli-responsive controlled release. The constructed Mb-Cu(2+)-gated MSN delivery system has promising applications in targeted drug therapy of tumors.

Chelating Langmuir-Blodgett film: a new versatile chemiluminescent sensing layer for biosensor applications

The present study reports the achievement of a new chemiluminescent sensing layer able to simultaneously (i) play an active role on ligand immobilization and (ii) serve as a catalyst in detection processes for label-free biosensor applications. This new type of active Langmuir-Blodgett (LB) monolayer has been designed by using a chelating lipid (Ni-NTA-DOGS). Thanks to the chelated metallic cation, this peculiar lipid exhibits luminol chemiluminescence catalysis properties in the presence of hydrogen peroxide. Upon biomolecule interaction through imidazole ring chelation (mediated by the metallic cation bound to the lipid headgroup), the chemiluminescent signal can be modulated. The first chemiluminescent signal acquisition experiments have shown a strong and homogeneous signal of the chelating layer. Upon histamine interactions, a histidine derivative used as a marker of fresh food quality, we succeeded in obtaining as a proof of concept a chemiluminescent signal variation without any derivatization of the target molecule. This signal variation was shown to be directly correlated to the histamine concentration with a limit of detection of 2 microg/mL.

Lipid membrane reorganization induced by chemical recognition

Nanoscale structural reorganization of a lipid bilayer membrane induced by a chemical recognition event has been imaged using in situ atomic force microscopy (AFM). Supported lipid bilayers, composed of distearylphosphatidylcholine (DSPC) and a synthetic lipid functionalized with a Cu(2+) receptor, phase-separate into nanoscale domains that are distinguishable by the 9 A height difference between the two molecules. Upon binding of Cu(2+) the electrostatic nature of the receptor changes, causing a dispersion of the receptor molecules and subsequent shrinking of the structural features defined by the receptors in the membrane. Complete reversibility of the process was demonstrated through the removal of metal ions with EDTA.

Structure analysis of soluble proteins using electron crystallography

Electron crystallography as a structural determination technique has grown dramatically in use over recent years. Improvements in microscopes, equipment, practical techniques, computation facilities and image processing methods are reflected in the increasing number of near-atomic resolution structures that have been published. In this review we shall summarize the techniques involved in structure determination of soluble proteins using electron crystallography. Many soluble protein structures have been investigated in this manner over the past two decades. Here we present several examples where a variety of approaches have been used to gradually increase the information obtained.

Two-dimensional crystallization of streptavidin: in pursuit of the molecular origins of structure, morphology, and thermodynamics

The streptavidin two-dimensional (2D) crystallization model has served as a paradigm for molecular self-assembly at interfaces. We have developed quantitative Brewster angle microscopy for the in situ measurement of spatially resolved relative protein surface densities. This allows investigation of both the thermodynamics and morphologies of 2D crystal growth. For crystal structure analysis, we employ TEM on grown crystals transferred to solid substrates. Comparison of results between commercially available streptavidin, recombinant streptavidin, and site-directed streptavidin mutants has provided insight into the protein protein and protein-lipid interactions that underlie 2D crystallization.