Synthetic molecular machines hold tremendous potential to revolutionize chemical and materials sciences. Their autonomous motion controlled by external stimuli allows to develop smart materials whose ...properties can be adapted on command. For the realisation of more complex molecular machines, it is crucial to design building blocks whose properties can be controlled by multiple orthogonal stimuli. A major challenge is to reversibly switch from forward to backward and again forward light-driven rotary motion using external stimuli. Here we report a push-pull substituted photo-responsive overcrowded alkene whose function can be toggled between that of a unidirectional 2
generation rotary motor and a molecular switch depending on its protonation and the polarity of its environment. With its simplicity in design, easy preparation, outstanding stability and orthogonal control of distinct forward and backward motions, we believe that the present concept paves the way for creating more advanced molecular machines.
Despite their enormous diversity in biological function and structure, peptides and proteins are endowed with properties that have induced and stimulated the development of peptidomimetics. Clearly, ...peptides can be considered as the “stem” of a phylogenetic molecular development tree from which branches of oligomeric peptidomimetics such as peptoids, peptidosulfonamides, urea peptidomimetics, as well as β‐peptides have sprouted. It is still a challenge to efficiently synthesize these oligomeric species, and study their structural and biological properties. Combining peptides and peptidomimetics led to the emergence of peptide–peptidomimetic hybrids in which one or more (proteinogenic) amino acid residues have been replaced with these mimetic residues. In scan‐like approaches, the influence of these replacements on biological activity can then be studied, to evaluate to what extent a peptide can be transformed into a peptidomimetic structure while maintaining, or even improving, its biological properties. A central issue, especially with the smaller peptides, is the lack of secondary structure. Important approaches to control secondary structure include the introduction of α,α‐disubstituted amino acids, or (di)peptidomimetic structures such as the Freidinger lactam. Apart from intra‐amino acid constraints, inter‐amino acid constraints for formation of a diversity of cyclic peptides have shaped a thick branch. Apart from the classical disulfide bridges, the repertoire has been extended to include sulfide and triazole bridges as well as the single‐, double‐ and even triple‐bond replacements, accessible by the extremely versatile ring‐closing alkene/alkyne metathesis approaches. The latter approach is now the method of choice for the secondary structure that presents the greatest challenge for structural stabilization: the α‐helix.
Building bridges: The design and development of peptidomimetics is an expanding research area and yields molecules that can improve on the function of their “natural” parent peptides—with tempting potential for novel therapeutics. We review here several different directions in exciting areas of oligomeric peptidomimetics, hybrids and covalent control of shape and secondary structure folding by alternatives to disulfide bridges.
Polyphosphazenes bearing cationic moieties were synthesized from poly(dichloro)phosphazene, which in turn was obtained by thermal polymerization of hexachlorocyclotriphosphazene in ...1,2,4-trichlorobenzene. Next, either 2-dimethylaminoethanol (DMAE) or 2-dimethylaminoethylamine (DMAEA) side groups were introduced by a substitution reaction. The polymers were purified by dialysis against water and tetrahydrofuran, lyophilized and evaluated as polymeric transfectants. The polyphosphazenes were able to bind plasmid DNA yielding positively charged particles (polyplexes) with a size around 80 nm at a polymer/DNA ratio of 3:1 (w/w). The polyphosphazene-based polyplexes were able to transfect COS-7 cells in vitro with an efficiency comparable to a well-known polymeric transfectant poly(2-dimethylaminoethyl methacrylate), pDMAEMA. The toxicity of both polyphosphazenes was lower than pDMAEMA. The transfection efficiency for the poly(DMAE)phosphazene-based polyplexes was about threefold higher in the absence of serum than in the presence of 5.0% fetal bovine serum. This is probably caused by unfavorable interactions of the polyplexes with serum proteins. In contrast, the poly(DMAEA)phosphazene-based polyplexes showed a threefold lower transfection activity in the absence of serum. For this system, serum proteins likely masked the toxicity of the polyplexes, as shown by the XTT cell viability assay and confocal laser scanning microscopy studies. Preliminary degradation studies indicate that the polymers were indeed degradable. The half-life at pH 7.5 and 37
°C was around 7 days for poly(DMAE)phosphazenes and 24 days for poly(DMAEA)phosphazenes. This study shows that polyphosphazenes are a suitable and promising new class of biodegradable polymeric carriers for gene delivery.
We present experimental proof that so-called “flowerlike micelles” exist and that they have some distinctly different properties compared to their “starlike” counterparts. Amphiphilic AB diblock and ...BAB triblock copolymers consisting of poly(ethylene glycol) (PEG) as hydrophilic A block and thermosensitive poly(N-isopropylacrylamide) (pNIPAm) B block(s) were synthesized via atom transfer radical polymerization (ATRP). In aqueous solutions, both block copolymer types form micelles above the cloud point of pNIPAm. Static and dynamic light scattering measurements in combination with NMR relaxation experiments proved the existence of flowerlike micelles based on pNIPAm16kDa-PEG4kDa-pNIPAm16kDa which had a smaller radius and lower mass and aggregation number than starlike micelles based on mPEG2kDa-pNIPAm16kDa. Furthermore, the PEG surface density was much lower for the flowerlike micelles, which we attribute to the looped configuration of the hydrophilic PEG block. 1H NMR relaxation measurements showed biphasic T2 relaxation for PEG, indicating rigid PEG segments close to the micelle core and more flexible distal segments. Even the flexible distal segments were shown to have a lower mobility in the flowerlike micelles compared to the starlike micelles, indicating strain due to loop formation. Taken together, it is demonstrated that self-assemblies of BAB triblock copolymers have their hydrophilic block in a looped conformation and thus indeed adopt a flowerlike conformation.
Two high-molecular-weight (>1000 kDa) water-soluble biopolymers, the main component of which was poly3-(3,4-dihydroxyphenyl)glyceric acid or polyoxy-1-carboxy-2-(3,4-dihydroxyphenyl)ethylene ...according to IR and NMR spectroscopy, were isolated from roots of Symphytum officinale. They exhibit antioxidant activity as expressed in a decrease of active oxygen species (AOS) by interfering directly in their formation process by polymorphonuclear neutrophils (PMN) and binding directly AOS.
A genetically engineered protein consisting of the 120 residues at the N‐terminus of human protein disulfide isomerase (PDI) has been characterized by 1H, 13C, and 15N NMR methods. The sequence of ...this protein is 35% identical to Escherichia coli thioredoxin, and it has been found also to have similar patterns of secondary structure and β‐sheet topology. The results confirm that PDI is a modular, multidomain protein. The last 20 residues of the N‐terminal domain of PDI are some of those that are similar to part of the estrogen receptor, yet they appear to be an intrinsic part of the thioredoxin fold. This observation makes it unlikely that any of the segments of PDI with similarities to the estrogen receptor comprise individual domains.
Background: Protein disulfide isomerase (PDI), a multifunctional protein of the endoplasmic reticulum, catalyzes the formation, breakage and rearrangement of disulfide bonds during protein folding. ...Dissection of this protein into its individual domains has confirmed the presence of the a and a′ domains, which are homologous to thioredoxin, having related structures and activities. The a and a′ domains both contain a –Cys–Gly–His–Cys– active-site sequence motif. The remainder of the molecule consists primarily of two further domains, designated b and b′ which are thought to be sequence repeats on the basis of a limited sequence similarity. The functions of the b and b′ domains are unknown and, until now, the structure of neither domain was known.
Results: Heteronuclear nuclear magnetic resonance (NMR) methods have been used to determine the global fold of the PDI b domain. The protein has an α/β fold with the order of the elements of secondary structure being β1–α1–β2–α2–β3–α3–β4–β5–α4. The strands are all in a parallel arrangement with respect to each other, except for β4 which is antiparallel. The arrangement of the secondary structure elements of the b domain is identical to that found in the a domain of PDI and in the ubiquitous redox protein thioredoxin; the three-dimensional folding topology of the b domain is also very similar to that of these proteins.
Conclusions: Our determination of the global fold of the b domain of PDI by NMR reveals that, like the a domain, the b domain contains the thioredoxin motif, even though the b domain has no significant amino-acid sequence similarities to any members of the thioredoxin family. This observation, together with indications that the b′ domain adopts a similar fold, suggests that PDI consists of active and inactive thioredoxin modules. These modules may have been adapted during evolution to provide PDI with its complete spectrum of enzymatic activities.
Here we report the first Staudinger ligations which yield tetra- and pentapeptides starting from
N-terminal α-azido peptides and
C-terminal peptide
o-(diphenylphosphine)phenyl esters. Mass ...spectrometric analysis of the reaction mixture provided a better insight into the mechanism of the Staudinger ligation and has been used to explain the observed intermediates and to optimize the ligation reaction. As a result, the optimized reaction enables the chemoselective coupling of peptides containing amino acids other than glycine at the ligation site.
Graphic
The chemotaxis inhibitory protein of
Staphylococcus aureus (CHIPS) is a 121 residue excreted virulence factor. It acts by binding the C5a- (C5aR) and formylated peptide receptor (FPR) and thereby ...blocks specific phagocyte responses. Here, we report the solution structure of a CHIPS fragment consisting of residues 31–121 (CHIPS
31-121). CHIPS
31-121 has the same activity in blocking the C5aR compared to full-length CHIPS, but completely lacks FPR antagonism. CHIPS
31-121 has a compact fold comprising an α-helix (residues 38–51) packed onto a four-stranded anti-parallel β-sheet. Strands β
2 and β
3 are joined by a long loop with a relatively well-defined conformation.
Comparison of CHIPS
31-121 with known structures reveals striking homology with the C-terminal domain of staphylococcal superantigen-like proteins (SSLs) 5 and 7, and the staphyloccocal and streptococcal superantigens TSST-1 and SPE-C. Also, the recently reported structures of several domains of the staphylococcal extracellullar adherence protein (EAP) show a high degree of structural similarity with CHIPS. Most of the conserved residues in CHIPS and its structural homologues are present in the α-helix. A conserved arginine residue (R46 in CHIPS) appears to be involved in preservation of the structure. Site-directed mutagenesis of all positively charged residues in CHIPS
31-121 reveals a major involvement of arginine 44 and lysine 95 in C5aR antagonism.
The structure of CHIPS
31-121 will be vital in the further unraveling of its precise mechanism of action. Its structural homology to
S.
aureus
SSLs, superantigens, and EAP might help the design of future experiments towards an understanding of the relationship between structure and function of these proteins.
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