5 research outputs found
Self-Assembly of High Molecular Weight Polypeptide Copolymers Studied via Diffusion Limited Aggregation
The
assembly of high molecular weight polypeptides into complex
architectures exhibiting structural complexity ranging from the nano-
to the mesoscale is of fundamental importance for various protein-related
diseases but also hold great promise for various nano- and biotechnological
applications. Here, the aggregation of partially unfolded high molecular
weight polypeptides into multiscale fractal structures is investigated
by means of diffusion limited aggregation and atomic force microscopy.
The zeta potential, the hydrodynamic radius, and the obtained fractal
morphologies were correlated with the conformation of the polypeptide
backbones as obtained from circular dichroism measurements. The polypeptides
are modified with polyethylene oxide side chains to stabilize the
polypeptides and to normalize intermolecular interactions. The modification
with the hydrophobic thioctic acid alters the folding of the polypeptide
backbone, resulting in a change in solution aggregation and fractal
morphology. We found that a more compact folding results in dense
and highly branched structures, whereas a less compact folded polypeptide
chain yields a more directional assembly. Our results provide first
evidence for the role of compactness of polypeptide folding on aggregation.
Furthermore, the mesoscale-structured biofilms were used to achieve
a hierarchical protein assembly, which is demonstrated by deposition
of Rhodamine-labeled HSA with the preassembled fractal structures.
These results contribute important insights to the fundamental understanding
of the aggregation of high molecular weight polypeptides in general
and provide opportunities to study nanostructure-related effects on
biological systems such as adhesion, proliferation, and the development
of, for example, neuronal cells
Convenient Approach to Polypeptide Copolymers Derived from Native Proteins
A convenient approach for the synthesis of narrowly dispersed
polypeptide
copolymers of defined compositions is presented. The controlled denaturation
of the proteins serum albumin and lysozyme followed by an in situ
stabilization with polyethylene(oxide) chains yields polypeptide side
chain copolymers of precisely defined backbone lengths as well as
the presence of secondary structure elements. Supramolecular architectures
are formed in solution because of the presence of hydrophobic and
hydrophilic amino acids along the polypeptide main chain. Polypeptide
copolymers reported herein reveal excellent solubility and stability
in aqueous media and no significant cytotoxicity at relevant concentrations,
and they can be degraded via proteolysis, which is very attractive
for biomedical applications. This “semi-synthetic chemistry”
approach is based on a novel and convenient concept for producing
synthetic polypeptides from native protein resources, which complements
traditional polypeptide synthesis and expression approaches and offers
great opportunities for the preparation of diverse polypeptides with
unique architectures
Quercetin Exhibits Preferential Binding Interaction by Selectively Targeting HRAS1 I‑Motif DNA-Forming Promoter Sequences
I-Motif (iM) DNA structures represent among the most
significant
noncanonical nucleic acid configurations. iM-forming DNA sequences
are found in an array of vital genomic locations and are particularly
frequent in the promoter islands of various oncogenes. Thus, iM DNA
is a crucial candidate for anticancer medicines; therefore, binding
interactions between iM DNA and small molecular ligands, such as flavonoids,
are critically important. Extensive sets of spectroscopic strategies
and thermodynamic analysis were utilized in the present investigation
to find out the favorable interaction of quercetin (Que), a dietary
flavonoid that has various health-promoting characteristics, including
anticancer properties, with noncanonical iM DNA structure. Spectroscopic
studies and thermal analysis revealed that Que interacts preferentially
with HRAS1 iM DNA compared with VEGF, BCL2 iM, and duplex DNA. Que,
therefore, emerged as a suitable natural-product-oriented antagonist
for targeting HRAS1 iM DNA. The innovative spectroscopic as well as
mechanical features of Que and its specific affinity for HRAS1 iM
may be useful for therapeutic applications and provide crucial insights
for the design of compounds with remarkable medicinal properties
Stealth Amphiphiles: Self-Assembly of Polyhedral Boron Clusters
This is the first
experimental evidence that both self-assembly
and surface activity are common features of all water-soluble boron
cluster compounds. The solution behavior of anionic polyhedral boranes
(sodium decaborate, sodium dodecaborate, and sodium mercaptododecaborate),
carboranes (potassium 1-carba-dodecaborate), and metallacarboranes
{sodium [cobalt bis(1,2-dicarbollide)]} was extensively studied, and
it is evident that all the anionic boron clusters form multimolecular
aggregates in water. However, the mechanism of aggregation is dependent
on size and polarity. The series of studied clusters spans from a
small hydrophilic decaborate-resembling hydrotrope to a bulky hydrophobic
cobalt bis(dicarbollide) behaving like a classical surfactant. Despite
their pristine structure resembling Platonic solids, the nature of
anionic boron cluster compounds is inherently amphiphilicthey
are stealth amphiphiles
DNA-Based Self-Assembly of Fluorescent Nanodiamonds
As
a step toward deterministic and scalable assembly of ordered
spin arrays we here demonstrate a bottom-up approach to position fluorescent
nanodiamonds (NDs) with nanometer precision on DNA origami structures.
We have realized a reliable and broadly applicable surface modification
strategy that results in DNA-functionalized and perfectly dispersed
NDs that were then self-assembled in predefined geometries. With optical
studies we show that the fluorescence properties of the nitrogen-vacancy
color centers in NDs are preserved during surface modification and
DNA assembly. As this method allows the nanoscale arrangement of fluorescent
NDs together with other optically active components in complex geometries,
applications based on self-assembled spin lattices or plasmon-enhanced
spin sensors as well as improved fluorescent labeling for bioimaging
could be envisioned