Does the cis/trans configuration of peptide bonds in bioactive tripeptides play a role in ACE-1 enzyme inhibition?

Abstract

Background: The milk casein-derived bioactive tripeptides isoleucine-proline-proline (IPP) and valine-proline-proline (VPP) have been shown to prevent development of hypertension in animal models and to lower blood pressure in moderately hypertensive subjects in most but not all clinical trials. Inhibition of angiotensin-converting enzyme 1 (ACE-1) has been suggested as the explanation for these antihypertensive and beneficial vascular effects. Previously, human umbilical vein endothelial cells (HUVEC) have not been used to test ACE-1 inhibiting properties of casein derived tripeptides in vasculature.

Purpose: We focused on the cis/trans configurations of the peptide bonds in proline-containing tripeptides in order to discover whether the different structural properties of these peptides influence their activity in ACE-1 inhibition. We hypothesized that the configuration of proline-containing peptides plays a significant role in enzyme inhibition.

Methods: AutoDock 4.2 docking software was used to predict suitable peptide bond configurations of the tripeptides. Besides modeling studies, we completed ACE-1 activity measurements in vitro using HUVEC cultures.

Results: In HUVEC cells, both IPP and VPP inhibited ACE-1. Based on molecular docking studies, we propose that in ACE-1 inhibition IPP and VPP share a similar cis configuration between the first aliphatic (isoleucine or valine) and the second (proline) amino acid residues and more different configurations between two proline residues. In vivo experiments are needed to validate the significance of the present findings.

Keywords: ACE inhibition; Autodock modeling; Ile-Pro-Pro; Val-Pro-Pro; vascular function.

Figure 1

Different cis/trans configurations of the peptide bond. Notes: (A) Peptide bonds values (ω1 and ω2) in IPP and VPP are 180° and they are both in trans configuration. (B) The first peptide bond (ω1) in IPP has 0° and the second (ω2) has 180° values and they are in cis and trans configuration, respectively. The first peptide bond (ω1) in VPP has 180° and the second (ω2) has 0° values and they are in trans and cis configuration, respectively. Abbreviations: IPP, isoleucine-proline-proline; VPP, valine-proline-proline.

Figure 2

Different cis/trans configurations of IPP. Notes: Different cis/trans configurations of the isoleucine-proline-proline are shown in global energy minimum structures. The shortest distances between carbonyl oxygens are provided. Blue color indicates nitrogen and red color oxygen atoms. Different peptide bond configurations of IPP are sorted by energy, from smallest to largest. Abbreviation: IPP, isoleucine-proline-proline.

Figure 3

Geometric isomers and omega values IPP and VPP Notes: Geometric isomers and omega values for IPP were ω1 =−42 and ω2 =−7, respectively. Geometric isomers and omega values for VPP were ω1 =−99 and ω2 =84 for VPP, respectively. These values were as predicted in the angiotensin-converting enzyme 1. Abbreviations: IPP, isoleucine-proline-proline; VPP, valine-proline-proline.

Figure 4

Angiotensin-converting enzyme 1 activity from HUVEC lysate. Notes: Angiotensin-converting enzyme 1 activity from HUVEC lysate incubated for 60 minutes with/without IPP or VPP peptides. Captopril was used as a reference inhibitor. Mean ± SEM, n=2–4, from duplicate measurements. **P<0.01; ***P<0.001 versus control. Abbreviations: HUVEC, human umbilical vein endothelial cells; IPP, isoleucine-proline-proline; VPP, valine-proline-proline; SEM, standard error of mean.

Figure 5

Tripeptide IPP in active site of ACE-1. Notes: Tripeptide IPP with omega values of ω1 =−42 and ω2 =−7 in active site of ACE-1. Autodock flexible residues are labeled, as are zinc (green) and its two histidine (383, 387) and glutamine (384) ligand residues. Abbreviations: IPP, isoleucine-proline-proline; ACE-1, angiotensin-converting enzyme 1.