In Situ Imaging of Pathological Collagen by Electrostatic Repulsion-Destabilized Peptide Probes

The development of robust collagen assays is crucial in the diagnosis and treatment of various pathological conditions. Peptide probes composed of the (Gly-Pro-Hyp)n sequences have received extensive attention for their remarkable collagen-targeting capability, which unfortunately has been severely impaired by their high triple helical stability. Herein, we report an efficient strategy to reduce the triple helical propensity of the (Gly-Pro-Hyp)n sequences by electrostatic repulsion. A series of peptides consisting of the (Gly-Pro-Hyp)7 sequence and a number of charged amino acid Asp have been investigated, indicating that the presence of six additional Asp pronouncedly weakened the triple helical stability of peptide probe FAM-PCTP-D6 under physiological conditions (pH 7.4). FAM-PCTP-D6 could be directly applied without any pretreatment to recognize denatured collagen with high selectivity, whereas another dye-labeled peptide probe ROX-PCTP-D6 specifically targeted pathological collagen in various connective tissues of animal disease models and human patients. The inclusion of extra charged natural amino acids has been demonstrated as a convenient approach to create biocompatible collagen-targeting peptide probes with much weaker triple helical stability. Without the need for preheating treatment, these electrostatic repulsion-driven peptide probes provide a handy tool for histopathology staining, showing promising applications in collagen-involved diseases.