Noncovalent Interactions with Proteins Modify the Physicochemical Properties of a Molecular Switch

Abstract

It is reported that spiropyran-aw idely investigated molecular photoswitch-can be stabilized in aqueous environments in the presence of av ariety of proteins, including human serum albumin, insulinf ibrils, lysozyme, and glucoseo xidase. The optical properties of the complexed photoswitch are protein dependent, with humans erum albumin providing the spiropyran with emission features previously observed for ap hotoswitch confined in media of high viscosity.D espite being bound to the protein molecules,s piropyranc an undergo ar ing-opening reactionu pon exposure to UV light. This photoisomerization process can affect the properties of the proteins:h ere, it is shown that the electrical conduction through humans erum albumin to which the spiropyran is bound increases following the ring-opening reaction.Bacteriorhodopsinh as long impressed scientists with the elegance with whichi tu ses the energy of sunlight to guide the motion of protons across cell membranes. This functioni se nabled by ap hotoswitchabler etinal moiety strategically positioned within the protein structure;light-induced isomerization of retinal triggersacascade of reactions, resulting in proton transfer against apHgradient. [1,2] Inspired by this and other examples, [3] chemists have developed different strategies to covalently immobilize photoswitchablem olecules within various biomacromolecules, [4][5][6][7][8][9] with the primary goal of controlling their structures and/or functions. Attractive and diverse applications have become possible, including photoswitchable enzymaticc atalysis [10,11] and light-actuated ion transport through ac hannel protein. [12] Herein, we considered as impler approach, which takes advantage of noncovalent interactions [13,14] between am olecular switch (in our case, spiropyran [15][16][17][18][19] )a nd the target protein. We found that av ariety of proteins, including human serum albumin (HSA), insulin, glucoseo xidase, and lysozyme can provide the spiropyran with good water solubility,i ndicating the formation of protein-spiropyranc omplexes. Within these complexes,s piropyran remained photoresponsive;h owever,i ts optical properties depended on which protein "host" it was bound to. We also found that photoisomerization of spiropyran bound to the serum albuminr esults in markedlyi ncreased electricalconduction through the protein.We worked with the most widely investigated spiropyran-1',3'-dihydro-1',3',3'-trimethyl-6-nitrospiro[2H-1-benzopyran-2,2'-(2H)-indole] (1,F igure 1a;S ection S1 in the Supporting Information). This compound is practically insoluble in water,a s evidenced by an experiment in which we injected 8.6 mLo f a3 .5 mm solutiono f1 in DMSO into 1mLo faphosphate-buffered saline (PBS;5m m phosphate, 70 mm NaCl, pH 8). The characteristic optical response of 1 disappeared within 4h,i ndicatingq uantitative precipitation (Figure 1b). However,w hen the same amount of 1 wasi njected into the buffer solution containing HSA at 30 mm (an equimolar ratio of 1 to the protein), the spiropyran remained soluble...

Reversible Photoisomerization of Spiropyran on the Surfaces of Au25 Nanoclusters

“…The resulting nanoclusters are characterized by opticala nd NMR spectroscopies as well as by mass spectrometry.Spiropyran bound to nanoclusters isomerizes in areversible fashion when exposed to UV and visible light, and its properties are similart ot hose of free spiropyran molecules in solution. The spectrum of the unique properties of nanoclustersc an be furtheri ncreased by functionalizing their surfaces with more complex molecules, such as spiropyran-au nique molecular switch responding to multiple external stimuli, [13] and, as such, an attractive building block for constructing novel molecular machines. [7] Here, we focused on the previously unexplored combination of two widely investigated species: 1) Au 25 nanoclusters and 2) the spiropyran molecular switch.…”

“…[7] Here, we focused on the previously unexplored combination of two widely investigated species: 1) Au 25 nanoclusters and 2) the spiropyran molecular switch. The spectrum of the unique properties of nanoclustersc an be furtheri ncreased by functionalizing their surfaces with more complex molecules, such as spiropyran-au nique molecular switch responding to multiple external stimuli, [13] and, as such, an attractive building block for constructing novel molecular machines. The vast majority of studies concerning this and other nanoclusters, however,h ave focused on clusters stabilized with simple ligands, typically 2phenylethanethiolate (PET).…”

“…Au 25 (SR) 18 ,w here SR denotes at hiolate ligand, represents the prototypical atomically precise gold nanoparticle [8] -a family of materials exhibiting ah ost of interesting optical, [9] catalytic, [10] magnetic, [11] and other [12] properties. The spectrum of the unique properties of nanoclustersc an be furtheri ncreased by functionalizing their surfaces with more complex molecules, such as spiropyran-au nique molecular switch responding to multiple external stimuli, [13] and, as such, an attractive building block for constructing novel molecular machines. The spectrum of the unique properties of nanoclustersc an be furtheri ncreased by functionalizing their surfaces with more complex molecules, such as spiropyran-au nique molecular switch responding to multiple external stimuli, [13] and, as such, an attractive building block for constructing novel molecular machines.…”

“…The vast majority of studies concerning this and other nanoclusters, however,h ave focused on clusters stabilized with simple ligands, typically 2phenylethanethiolate (PET). The spectrum of the unique properties of nanoclustersc an be furtheri ncreased by functionalizing their surfaces with more complex molecules, such as spiropyran-au nique molecular switch responding to multiple external stimuli, [13] and, as such, an attractive building block for constructing novel molecular machines. [14] Ligand-protected gold nanoclustersa re typicallyp repared by reducing an Au I precursor with NaBH 4 in the presence of ac orresponding thiol.…”

Photo-Responsive Graphene and Carbon Nanotubes to Control and Tackle Biological Systems

“…On the other hand, studies on the degradation process of the molecule has evidenced how the hydrolysis of the compound occurs already after 24 h of exposure, which could represent a limitation for the in vivo applications of these compounds. Several studies have focused on the applications of SP entities in biological environments, as examples the interaction between SP and MC forms with a large variety of proteins (Amdursky et al, 2016 ), from human serum albumin (HSA) and insulin to lysozyme, has been investigated. These studies have evidenced that the optical properties of the photochromic entity are maintained upon its interaction with the protein but they are influenced by the presence of the proteins itself.…”