Blue-Light-Triggered Photorelease of Active Chemicals Captured by the Flavoprotein Dodecin

Surface Plasmon-Assisted Fluorescence Enhancing and Quenching: From Theory to Application

The integration of surface plasmon resonance and fluorescence yields a multiaspect improvement in surface fluorescence sensing and imaging, leading to a paradigm shift of surface plasmon-assisted fluorescence techniques, for example, surface plasmon enhanced field fluorescence spectroscopy, surface plasmon coupled emission (SPCE), and SPCE imaging. This Review aims to characterize the unique optical property with a common physical interpretation and diverse surface architecture-based measurements. The fundamental electromagnetic theory is employed to comprehensively unveil the fluorophore-surface plasmon interaction, and the associated surface-modification design is liberally highlighted to balance the surface plasmon-induced fluorescence-enhancement efforts and the surface plasmon-caused fluorescence-quenching effects. In particular, all types of surface structures, for example, silicon, carbon, protein, DNA, polymer, and multilayer, are systematically interrogated in terms of component, thickness, stiffness, and functionality. As a highly interdisciplinary and expanding field in physics, optics, chemistry, and surface chemistry, this Review could be of great interest to a broad readership, in particular, among physical chemists, analytical chemists, and in surface-based sensing and imaging studies.

Dodecin as carrier protein for immunizations and bioengineering applications

In bioengineering, scaffold proteins have been increasingly used to recruit molecules to parts of a cell, or to enhance the efficacy of biosynthetic or signalling pathways. For example, scaffolds can be used to make weak or non-immunogenic small molecules immunogenic by attaching them to the scaffold, in this role called carrier. Here, we present the dodecin from Mycobacterium tuberculosis (mtDod) as a new scaffold protein. MtDod is a homododecameric complex of spherical shape, high stability and robust assembly, which allows the attachment of cargo at its surface. We show that mtDod, either directly loaded with cargo or equipped with domains for non-covalent and covalent loading of cargo, can be produced recombinantly in high quantity and quality in Escherichia coli. Fusions of mtDod with proteins of up to four times the size of mtDod, e.g. with monomeric superfolder green fluorescent protein creating a 437 kDa large dodecamer, were successfully purified, showing mtDod's ability to function as recruitment hub. Further, mtDod equipped with SYNZIP and SpyCatcher domains for post-translational recruitment of cargo was prepared of which the mtDod/SpyCatcher system proved to be particularly useful. In a case study, we finally show that mtDod-peptide fusions allow producing antibodies against human heat shock proteins and the C-terminus of heat shock cognate 70 interacting protein (CHIP).

Flavin Storage and Sequestration by Mycobacterium tuberculosis Dodecin

Dodecins are small flavin binding proteins occurring in archaea and bacteria. They are remarkable for binding dimers of flavins with their functional relevant aromatic isoalloxazine rings deeply covered. Bacterial dodecins are widely spread and found in a large variety of pathogens, among them Pseudomonas aeruginosa, Streptococcus pneumonia, Ralstonia solanacearum, and Mycobacterium tuberculosis ( M. tuberculosis). In this work, we seek to understand the function of dodecins from M. tuberculosis dodecin. We describe flavin binding in thermodynamic and kinetic properties and achieve mechanistic insight in dodecin function by applying spectroscopic and electrochemical methods. Intriguingly, we reveal a significant pH dependence in the affinity and specificity of flavin binding. Our data give insight in M. tuberculosis dodecin function and advance the current understanding of dodecins as flavin storage and sequestering proteins. We suggest that the dodecin in M. tuberculosis may specifically be important for flavin homeostasis during the elaborate lifestyle of this organism, which calls for the evaluation of this protein as drug target.

Nanomechanical properties of protein-DNA layers with different oligonucleotide tethers

The length and flexibility of the oligonucleotide tethers strongly affect the viscoelastic properties of the resulting protein–DNA layers.

The multi-ligand binding flavoprotein dodecin is reconstituted on top of flavin-terminated oligonucleotide monolayers. A detailed quartz crystal microbalance with a dissipation monitoring (QCM-D) study showing how the length and flexibility of the oligonucleotide tethers influence the stability and the viscoelastic properties of the resulting DNA–protein layers is presented. Relatively dense protein layers can be obtained, if the length of the tethers is in the same range as the diameter of dodecin. When significantly longer tethers are used, less dense layers are formed. When rather short tethers are used, the reaching area of individual tethers is too low to capture single apododecin molecules cooperatively, and the formation of stable and dense protein layers is not possible. On top of the DNA–dodecin layers additional flavin–DNA ligands may be captured to form sandwich-type DNA–protein–DNA layers. Differences in the binding and unbinding behavior of flavin-dsDNA and flavin-ssDNA ligands are measured by QCM-D and surface plasmon fluorescence spectroscopy (SPFS). Both type of ligands show relatively low k_on values, which might be explained by the structural rigidity of the binding pockets allowing a ligand to enter only when it approaches precisely in the right orientation. Apparently apododecin–flavin binding follows Fischer's classic lock-and-key binding model.

Multi-Ligand-Binding Flavoprotein Dodecin as a Key Element for Reversible Surface Modification in Nano-biotechnology

In this paper the multiple (re)programming of protein-DNA nanostructures comprising generation, deletion, and reprogramming on the same flavin-DNA-modified surface is introduced. This work is based on a systematic study of the binding affinity of the multi-ligand-binding flavoprotein dodecin on flavin-terminated DNA monolayers by surface plasmon resonance and quartz crystal microbalance with dissipation (QCM-D) measurements, surface plasmon fluorescence spectroscopy (SPFS), and dynamic AFM force spectroscopy. Depending on the flavin surface coverage, a single apododecin is captured by one or more surface-immobilized flavins. The corresponding complex binding and unbinding rate constants kon(QCM) = 7.7 × 10(3) M(-1)·s(-1) and koff(QCM) = 4.5 × 10(-3) s(-1) (Kd(QCM) = 580 nM) were determined by QCM and were found to be in agreement with values for koff determined by SPFS and force spectroscopy. Even though a single apododecin-flavin bond is relatively weak, stable dodecin monolayers were formed on flavin-DNA-modified surfaces at high flavin surface coverage due to multivalent interactions between apododecin bearing six binding pockets and the surface-bound flavin-DNA ligands. If bi- or multivalent flavin ligands are adsorbed on dodecin monolayers, stable sandwich-type surface-DNA-flavin-apododecin-flavin ligand arrays are obtained. Nevertheless, the apododecin flavin complex is easily and quantitatively disassembled by flavin reduction. Binding and release of apododecin are reversible processes, which can be carried out alternatingly several times to release one type of ligand by an external redox trigger and subsequently replace it with a different ligand. Hence the versatile concept of reprogrammable functional biointerfaces with the multi-ligand-binding flavoprotein dodecin is demonstrated.