Cis-trans isomerization of peptoid residues in the collagen triple-helix.

Cis-peptide bonds are rare in proteins, and building blocks less favorable to the trans-conformer have been considered destabilizing. Although proline tolerates the cis-conformer modestly among all amino acids, for collagen, the most prevalent proline-abundant protein, all peptide bonds must be trans to form its hallmark triple-helix structure. Here, using host-guest collagen mimetic peptides (CMPs), we discover that surprisingly, even the cis-enforcing peptoid residues (N-substituted glycines) form stable triple-helices. Our interrogations establish that these peptoid residues entropically stabilize the triple-helix by pre-organizing individual peptides into a polyproline-II helix. Moreover, noting that the cis-demanding peptoid residues drastically reduce the folding rate, we design a CMP whose triple-helix formation can be controlled by peptoid cis-trans isomerization, enabling direct targeting of fibrotic remodeling in myocardial infarction in vivo. These findings elucidate the principles of peptoid cis-trans isomerization in protein folding and showcase the exploitation of cis-amide-favoring residues in building programmable and functional peptidomimetics.

Terminal repeats impact collagen triple-helix stability through hydrogen bonding.

Nearly 30% of human proteins have tandem repeating sequences. Structural understanding of the terminal repeats is well-established for many repeat proteins with the common α-helix and ß-sheet foldings. By contrast, the sequence-structure interplay of the terminal repeats of the collagen triple-helix remains to be fully explored. As the most abundant human repeat protein and the most prevalent structural component of the extracellular matrix, collagen features a hallmark triple-helix formed by three supercoiled polypeptide chains of long repeating sequences of the Gly-X-Y triplets. Here, with CD characterization of 28 collagen-mimetic peptides (CMPs) featuring various terminal motifs, as well as DSC measurements, crystal structure analysis, and computational simulations, we show that CMPs only differing in terminal repeat may have distinct end structures and stabilities. We reveal that the cross-chain hydrogen bonding mediated by the terminal repeat is key to maintaining the triple-helix's end structure, and that disruption of it with a single amide to carboxylate substitution can lead to destabilization as drastic as 19 °C. We further demonstrate that the terminal repeat also impacts how strong the CMP strands form hybrid triple-helices with unfolded natural collagen chains in tissue. Our findings provide a spatial profile of hydrogen bonding within the CMP triple-helix, marking a critical guideline for future crystallographic or NMR studies of collagen, and algorithms for predicting triple-helix stability, as well as peptide-based collagen assemblies and materials. This study will also inspire new understanding of the sequence-structure relationship of many other complex structural proteins with repeating sequences.

Molecular Imaging of Collagen Destruction of the Spine.

As the leading cause of disability worldwide, low back pain is commonly caused by biomechanical and catabolic disruptions to key structures of the spine, such as intervertebral discs and facet joints. To date, accurate, noninvasive detection of microdestruction within these tissues remains an elusive goal. Here, we report an in vivo imaging approach based on a collagen hybridizing peptide (CHP) that specifically targets disruption to the extracellular matrix architecture at the molecular scale─the denatured collagen molecules. Utilizing fluorescently labeled CHPs, live animal imaging, and light sheet fluorescence microscopy, we mapped collagen destruction in the lumbar spines in 3D, revealing that under normal conditions collagen destruction was localized to load-bearing anatomical structures including annulus fibrosus of the disc and the facet joints, where aging, tensile force (hindlimb suspension), and disc degeneration (needle puncture) escalated the CHP-binding in specific mouse models. We showed that targeting denatured collagen molecules allowed for an accurate, quantifiable interrogation of the structural integrity of these spinal matrixes with a greater sensitivity than anatomical imaging and histology. Finally, we demonstrated CHP's binding to degenerated human discs, suggesting exciting potentials for applying CHP for diagnosing, monitoring, and treating various spinal disorders, including intervertebral disc degeneration, facet joint osteoarthritis, and ankylosing spondylitis.

Structure-guided design and synthesis of isoflavone analogs of GW4064 with potent lipid accumulation inhibitory activities.

Our group has previously reported a series of isoflavone derivatives with antidyslipidemic activity. With this background, a series of isoflavone analogs of GW4064 were designed, synthesized and evaluated the lipid-lowering activity of analogs. As a result, most of compounds significantly reduced the lipid accumulation in 3T3-L1 adipocytes and four of them (10a, 11, 15c and 15d) showed stronger inhibitory than GW4064. The most potent compound 15d exhibited promising agonistic activity for FXR in a cell-based luciferase reporter assay. Meanwhile, 15d up-regulated FXR, SHP and BSEP gene expression and down-regulated the mRNA expression of lipogenesis gene SREBP-1c. Besides, an improved safety profile of 15d was also observed in a HepG2 cytotoxicity assay compared with GW4064. The obtained biological results were further confirmed by a molecular docking study showing that 15d fitted well in the binding pocket of FXR and interacted with some key residues simultaneously.

Lipid accumulation inhibitory activities of novel isoxazole-based chenodeoxycholic acids: Design, synthesis and preliminary mechanism study.

In continuation of our drug discovery program on hyperlipidemia, a series of novel isoxazole-chenodeoxycholic acid hybrids were designed, synthesized and evaluated for their lipid-lowering effects. Preliminary screening of all the synthesized compounds was done by using a 3T3-L1 adipocyte model, in which the most active compound 16b could significantly reduce the lipid accumulation up to 30.5% at a nontoxic concentration 10 µM. Further mechanism studies revealed that 16b blocked lipid accumulation via activating FXR-SHP signaling pathway, efficiently down-regulated the expression of key lipogenesis regulator SREBP-1c.

Lipid reducing activity of novel cholic acid (CA) analogs: Design, synthesis and preliminary mechanism study.

Bile acids, initially discovered as endogenous ligands of farnesoid X receptor (FXR), play a central role in the regulation of triglyceride and cholesterol metabolism and have recently emerged as a privileged structure for interacting with nuclear receptors relevant to a large array of metabolic processes. In this paper, phenoxy containing cholic acid derivatives with excellent drug-likeness have been designed, synthesized, and assayed as agents against cholesterol accumulation in Raw264.7 macrophages. The most active compound 14b reduced total cholesterol accumulation in Raw264.7 cells up to 30.5% at non-toxic 10 µM and dosage-dependently attenuated oxLDL-induced foam cell formation. Western blotting and qPCR results demonstrate that 14b reduced both cholesterol and lipid in Raw264.7 cells through (1) increasing the expression of cholesterol transporters ABCA1 and ABCG1, (2) accelerating ApoA1-mediated cholesterol efflux. Through a cell-based luciferase reporter assay and molecular docking analysis, LXR was identified as the potential target for 14b. Interestingly, unlike conventional LXR agonist, 14b did not increase lipogenesis gene SREBP-1c expression. Overall, these diverse properties disclosed herein highlight the potential of 14b as a promising lead for further development of multifunctional agents in the therapy of cardiovascular disease.