The collagen-like peptide (GER)(15)GPCCG forms pH-dependent covalently linked triple helical trimers

A collagen-like peptide with the sequence (GER)(15) GPCCG was synthesized t o study the formation of a triple helix in the absence of proline residues. This peptide can form a triple helix at acidic and basic pH, but is insolu ble around neutral pH. The formation of a triple helix can be used to coval ently oxidize the cysteine residues into a disulfide knot. Three disulfide bonds are formed between the three chains as has been found at the carboxyl -terminal end of the type III collagen triple helix. This is a new method t o covalently link collagenlike peptides with a stereochemistry that occurs in nature. The peptide undergoes a reversible, cooperative triple helix rev ersible arrow coil transition with a transition midpoint (T-m) of 17 to 20 degrees C at acidic pH and 32 to 37 degrees C at basic pH. At acidic pH the re was little influence of the T-m on the salt concentration of the buffer. At basic pH increasing the salt concentration reduced the T-m to values co mparable to the stability at acidic pH. These experiments show that the tri peptide unit GER which occurs frequently in collagen sequences can form a t riple helical structure in the absence of more typical collagen-like tripep tide units and that charge-charge interactions play a role in the stabiliza tion of the triple helix of this peptide.