Insights into cardiovascular effects of proline-rich oligopeptide ( Bj -PRO-10c) revealed by structure–activity analyses: dissociation of antihypertensive and bradycardic effects

We have previously reported that the proline-rich decapeptide from Bothrops jararaca ( Bj -PRO-10c) causes potent and sustained antihypertensive and bradycardic effects in SHR. These activities are independent of ACE inhibition. In the present study, we used the Ala-scan approach to evaluate the importance of each amino acid within the sequence of Bj -PRO-10c (Pyr 1 -Asn 2 -Trp 3 -Pro 4 -His 5 -Pro 6 -Gln 7 -Ile 8 -Pro 9 -Pro 10 ). The antihypertensive and bradycardic effects of the analogues Bj -PRO-10c Ala 3 , Bj -PRO-10c Ala 7 , Bj -PRO-10c Ala 8 were similar to those of Bj -PRO-10c, whereas the analogues Bj -PRO-10c Ala 2 , Bj -PRO-10c Ala 4 , Bj -PRO-10c Ala 5 , Bj -PRO-10c Ala 9 , and Bj -PRO-10c Ala 10 kept the antihypertensive activity and lost bradycardic activity considerably. In contrast, Bj -PRO-10c Ala 1 and Bj -PRO-10c Ala 6 were unable to provoke any cardiovascular activity. In summary, we demonstrated that (1) the Pyr 1 and Pro 6 residues are essential for both, the antihypertensive and bradycardic effects of Bj -PRO-10c; (2) Ala-scan approach allowed dissociating blood pressure reduction and bradycardic effects. Conformational properties of the peptides were examined by means of circular dichroism (CD) spectroscopy. The different Ala-scan analogues caused either an increase or decrease in the type II polyproline helix content compared to Bj -PRO-10c. The complete loss of activity of the Pro 6 → Ala 6 mutant is probably due to the fact that in the parent peptide the His 5 -Pro 6 bond can exist in the cis configuration, which could correspond to the conformation of this bond in the bound state. Current data support the Bj -PRO-10c as a promising leader prototype to develop new agents to treat cardiovascular diseases and its co-morbidities.