Structure–function studies of Tityus serrulatus Hypotensin-I (TsHpt-I): A new agonist of B2 kinin receptor

In order to better understand the relationship between the primary structure of TsHpt-I - a bradykinin-potentiating peptide (BPP) isolated from the venom of the yellow scorpion Tityus serrulatus, with a non-canonical Lys residue prior to the conservative Pro-Pro doublet - and its cardiovascular effects, a series of ladder peptides were synthesized using the C-terminal portion of TsHpt-I as a template. All synthetic peptides having the Pro-Pro doublet at their C-terminal were able to potentiate the hypotensive effect of bradykinin. Conversely, only those analogues having Lys residue could induce a transient hypotension when intravenously administrated in male rats, indicating that the positive charge located toward the radical of this amino acid residue is crucial for this cardiovascular effect. Differently from all known BPPs, TsHpt-I acts as an agonist of the B2 receptor and does not inhibit angiotensin-converting enzyme. The capacity of this peptide to activate this subtype of kinin receptor, releasing NO, was also affected by the absence of Lys' side-chain positive charge. Moreover, this study has demonstrated that the minimization of the primary structure of TsHpt-I does not significantly alter the biological effects of this native peptide, which could be of interest for biotechnological purposes.