What we do - about us
Triple Helical Peptides synthesises and distributes collagen-like peptides,
primarily for research use. The specificity of the peptide for particular targets depends upon the peptide sequence, and also on its triple-helical conformation. This is an important property - linear versions of our peptides (which we can supply as control materials) are generally not active and do not engage the target protein. In nature, the triple-helical conformation of collagen (a Glycine-Xaa-Yaa polymer) is maintained by the presence of high levels of Proline at position X, and its post-translationally modified derivative, 4-Hydroxyproline, at position Y. This unique primary structure allows nascent collagen to fold into a triple-helix. Native collagen unfolds (melts) at around body temperature and is stabilised by assembling into a higher-order structure, the collagen fibre, in which there are extensive contacts between triple-helical tropocollagen molecules, and particularly, covalent crosslinks formed between adjacent tropocollagens.
Our peptides adopt triple-helical structure by virtue of their high levels of Proline at X and Hydroxyproline at Y.
Single-letter amino acid nomenclature is used hereafter, where G = Glycine, P = Proline and O = Hydroxyproline. GPO polymers can be very stable, unfolding at 50°C or more, depending on their length, but specific sequences that deviate from this canonical require stabilising flanking sequences, typically GPP polymer extensions on each side of the sequence of interest.
Typically, our triple-helical peptides (THPs) are platelet agonists, used in the measurement of platelet activation by collagen, through the main collagen signalling receptor, Glycoprotein VI (GPVI).
They can be applied in Platelet-Rich Plasma, e.g., for platelet aggregation, in washed platelet suspensions, or as adhesive coatings in 96-well plate or flowing blood studies. GPVI ligands require the presence of O to bind to the receptor, and a simple GPO polymer can be effective. Our GPVI ligands are described in the Products section.
A distinct class of THP is recognised by the collagen-binding integrins, α1β1, α2β1, α10β1 and α11β1.
The integrin-binding THPs have the general form, Gxx'GEx'', with the main example being GFOGER that
is recognised by all of this class of integrin. Various hydrophobic residues will substitute for x,
and occasionally, motifs are found with residues other than O at X' or R at x''.
These variants display different selectivity for the different collagen-binding integrins.
Integrin α2β1 is the only family member expressed on the platelet surface, so GFOGER is also
a useful platelet-adehsive ligand.
Another useful peptide for platelet research binds the A3 domain of
von Willebrand Factor (VWF). The VWF A3-binding motif is GP(R/A)GQOGVMGFO.
In vivo, VWF is captured by collagen exposed through damage to the endothelial lining of the blood vessel. Thus, VWF A3 binds to collagen, its conformation changes and the A1 domain is exposed so that it can bind Glycoprotein Ib (GPIb) on the platelet surface. The circulating platelet becomes tethered to the vessel wall, where it is activated by GPO-containing tracts of collagen that bind GPVI, and its adhesion is consolidated by interaction with integrin-binding motifs.
The Collagen Toolkits (now called the Collagen Ligands Collection)
are sets of overlapping THPs that can be used to map the binding sites for a range of different molecules to collagen. This allows a series of peptides to be synthesised to pinpoint the exact binding motif, from which more specific ligands can be created to manipulate the target molecule, for example to create complexes for structural studies, or as ligand pairs for use in HTS work. The prototype Toolkit was made by Graham Knight in 1998, based upon a fragment of the Collagen I α1 chain, from which GFOGER was identified as an integrin α2β1-binding motif (2000), and the first integrin-ligand complex structure (2000) soon followed. The subsequent Toolkits II and III (2007/8), made by Nico Raynal, Dominique Bihan and Arkadiusz Bonna in the Farndale Lab have led to several co-crystals of collagen-binding proteins.
Triple Helical Peptides is now marketing the Toolkits
as the Collagen Ligands Collection,
a name that better reflects their function and purpose.