Collagen hybridizing peptide
A collagen hybridizing peptide (CHP) is a synthetic
Collagen, CHP, CMP, and CLP
Collagen is the main component of the extracellular matrix (ECM).[7] The collagen superfamily consists of 28 different types of collagen.[7] Although the function and hierarchical structure of these collagens may vary, they all share the defining structural feature known as the triple helix,[1] where three left handed polyproline II-type (PPII) helices assemble to form a right-handed supercoiled helical motif.[1][8] Short synthetic peptides known as collagen mimetic peptides (CMPs) or collagen-like peptides (CLPs) have played a major role in elucidating the 3D structure of the collagen triple helix, its folding kinetics, and thermal stability as small triple helical models.[3][9][10][11] CMPs, CLPs, and CHPs are all very similar in terms of their amino acid sequences but only when CMPs or CLPs are heated above their melting temperatures, do they exist in the dissociated, single-stranded state and can be considered as CHPs.[2]
Binding mechanism
Single-stranded CHPs bind to denatured collagen chains and
Denatured collagen as a biomarker for tissue remodelling and damage
Controlled collagen turnover is crucial for embryonic development, organ morphogenesis, as well as tissue maintenance and repair.
Most methods for the evaluation of collagen denaturation in disease states are indirect, such as detecting matrix metalloproteinase (MMP) activity or quantifying collagen peptide fragments in urine, serum, or synovial fluid.[18][19][20] Using conventional methods for directly targeting collagen, researchers have to relied on collagen binding peptides selected by phage display,[21] derived from collagen binding proteins,[22] or antibodies raised against collagens. Unfortunately, these compounds cannot target denatured collagens which are unstructured and do not present a defined 3D epitope. In addition, antibodies that were reported to distinguish specific degraded collagen fragments can only recognize one or few collagen types.[2][23] In contrast, CHPs, in principle, can bind to all types of denatured collagens.[4][5][6]
Applications
Tissue staining
Fluorophore- or biotin-labeled CHPs are used as a staining agent for detecting collagen degradation and denaturation via immunofluorescence and immunohistochemistry applications.[5] CHPs can stain frozen tissue sections, formalin-fixed paraffin embedded (FFPE) sections,[5] as well as fresh tissues.[14][15] CHP is applicable to tissue specimens from multiple species and a range of diseases, such as myocardial infarction, arthritis, nephritis, and fibrosis.[5]
In vivo imaging
CHPs can also be labelled with near-infrared fluorophores for in vivo fluorescent imaging.[13][24]
Collagen identification
CHPs can be used for visualizing many different types of collagen bands in SDS-PAGE gels.[6] Collagen is denatured by heating in the presence of SDS prior to loading the gel. The collagen bands are visualized through CHP-collagen hybridization when the gels are stained by fluorescently-labeled CHPs.[6]
Detecting mechanical damage to connective tissue
Collagen offers mechanical strength in load bearing tissues in the body such as tendons, ligaments, and bone. As forces are applied to these tissues, the collagen triple helix can be damaged and unwind, and CHPs allow for molecular level detection of mechanical damage in such connective tissues.[15][25]
References
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