Imaging and targeting LOX-mediated tissue remodeling with a reactive collagen peptide.

Collagens are fibrous proteins that are integral to the strength and stability of connective tissues. During collagen maturation, lysyl oxidases (LOX) initiate the cross-linking of fibers, but abnormal LOX activity is associated with impaired tissue function as seen in fibrotic and malignant diseases. Visualizing and targeting this dynamic process in healthy and diseased tissue is important, but so far not feasible. Here we present a probe for the simultaneous monitoring and targeting of LOX-mediated collagen cross-linking that combines a LOX-activity sensor with a collagen peptide to chemoselectively target endogenous aldehydes generated by LOX. This synergistic probe becomes covalently anchored and lights up in vivo and in situ in response to LOX at the sites where cross-linking occurs, as demonstrated by staining of normal skin and cancer sections. We anticipate that our reactive collagen-based sensor will improve understanding of collagen remodeling and provide opportunities for the diagnosis of fibrotic and malignant diseases.

Alkylation of γ-Azaproline Creates Conformationally Adaptable Proline Derivatives for pH-Responsive Collagen Triple Helices.

Cγ -substituted proline derivatives are valuable tools for developing functionalized collagen peptides for biological and materials investigations, yet the stereochemistry at Cγ can produce undesired steric or stereoelectronic constraints. Alkylated γ-azaproline (γ-azPro) derivatives are proline mimetics that lack a stereogenic center at the γ-position of the ring and can thus utilize the invertibility of nitrogen to adapt their conformation. NMR spectroscopic analyses and DFT calculations highlighted how alkylated γ-azPro derivatives are conformationally dynamic and adopt conformational preferences through ring pucker flip along with nitrogen inversion. Lastly, incorporation of alkylated γ-azPro into collagen peptides produced functionalized pH-responsive triple helices with similar thermal stabilities, regardless of their placement in the Xaa or Yaa position within the characteristic Xaa-Yaa-Gly repeating unit of collagen peptides.

γ-Azaproline Confers pH†Responsiveness and Functionalizability on Collagen Triple Helices.

Proline derivatives bearing substituents at Cγ are valuable tools for biological and materials investigations. However, the stereochemistry at Cγ can produce undesired steric or stereoelectronic interactions. Here, we introduce γ-azaproline (γ-azPro), which lacks a stereogenic center at Cγ, as a pH-responsive and functionalizable proline analogue that can adapt to its environment. Conformational analyses by NMR spectroscopy and DFT calculations revealed that the imidazolidine ring of γ-azPro is flexible. Incorporation of γ-azPro into collagen model peptides (CMPs) produced pH-responsive triples helices and triple helices that can be easily functionalized.

Oligoprolines as Molecular Entities for Controlling Distance in Biological and Material Sciences.

Nature utilizes large biomolecules to fulfill tasks that require spatially well-defined arrangements at the molecular level such as electron transfer, ligand-receptor interactions, or catalysis. The creation of synthetic molecules that enable precise control over spacing and functionalization provides opportunities across diverse disciplines. Key requirements of functionalizable oligomeric scaffolds include the specific control of their molecular properties where the correct balance of flexibility and rigidity must be maintained in addition to the prerequisite of defined length. These molecules must ideally be equally applicable in aqueous and organic environments, they must be easy to synthesize in a controlled stepwise fashion, and they must be easily modified with a palette of chemical appendages having diverse functionalities. Oligoproline, a peptidic polymer comprised of repeating units of the amino acid proline, is an ideal platform to meet such challenges. Oligoproline derives its characteristic rigidity and well-defined secondary structure from the innate features of proline. It is the only naturally occurring amino acid that has its side-chain cyclized to its α-amino group, generating often-populated trans and cis conformers around the tertiary amide bonds formed in proline oligomers. Oligoprolines are widely applied to define distance on the molecular level as they are capable of serving as both a "molecular ruler" with a defined length and as a "molecular scaffold" with precisely located and predictably oriented substitutions along the polymeric backbone. Our investigations focus on the use of oligoproline as a molecular scaffold. Toward this end, we have investigated the role of solvent upon helical structure of oligoproline, and the effect that substituents on the pyrrolidine ring and the oligomer termini have on the stability of the helix. We have also further explored the molecular characteristics of oligoproline through spectroscopic and crystallographic methods. All of these structural insights laid the basis for implementation of oligoproline in materials science and chemical biology. Within this Account, we highlight the value of oligoprolines for applications in distinctly different research areas. Toward materials chemistry, we have utilized oligoprolines for the size-controlled generation of noble metal nanoparticles, and to probe the role of spatial preorganization of π-systems for molecular self-assembly. Within the biological realm, we have applied oligoprolines to probe the role of distance on G-protein coupled receptor-mediated ligand uptake by cancerous cells and to investigate the effects of charge preorganization on the efficacy of cationic cell-penetrating peptides.