Casein accounts for of the total protein
Casein accounts for 80% of the total protein in bovine milk (Capriotti, Cavaliere, Piovesana, Samperi, & Laganà, 2016); hydrolysates or bioactive peptides derived from casein have been employed widely in food as a functional ingredient (Capriotti et al., 2016, Field et al., 2008). Many studies have demonstrated that certain peptides from bovine caseins possess bioactivities, including antioxidant, antibacterial, antithrombotic and antihypertensive effects. These bioactive peptides can be acquired through enzymatic hydrolysis (Korhonen & Pihlanto, 2006).
To elaborate the active mechanisms of novel ACE-inhibitory peptides, in silico methods tend to be used to predict the theoretical bioactivities likelihood of the potential peptides, especially Quantitative structure–activity relationship (QSAR) method, which have been widely applied to study the relationships of the peptides’ primary structure and the ACE inhibitory activities of the peptides (Wu, Aluko, & Nakai, 2010). In recent years, the physicochemical characteristics have also been taken into consideration in the research of bioactive peptides, such as antimicrobial and ACEI peptides (Luna Vital et al., 2014, Yang et al., 2012). Several online tools have been developed for this, such as the isoelectric point and molecular weight, which can be analyzed by the online tool of Expasy-Compute pI/Mw. ProtParam Tool has the function of predicting the grand average of hydropathicity (GRAVY) and instability index of peptides. The PepDraw Tool was used to analyze the net charge and hydrophobicity of the peptides. In addition to elaborate the primary structures of ACEI peptides, several researchers have started to analyze the relationships between the secondary structure of the peptides and their ACEI activities (Yu, Zhao, Liu, Lu, & Chen, 2011). Moreover, as the elucidating of the crystal structure of the human ACE and its inhibitor complex, the molecular docking method has generally been employed to analyzing the action mechanism analysis of ACEI peptides (Xie, Choung, Cao, Lee, & Choi, 2015).
In this study, the sequences of the peptides derived from casein hydrolysate by tryptic ddhUTP were determined by UPLC-Q-TOF-MS/MS. A novel ACEI peptide was identified and subsequently synthesized. The IC50 value of the synthesized peptide was determined and the inhibition mode of the peptide was explored by adopting Lineweaver-Burk plots. We also elucidated the potential mechanism of ACEI activity by using molecular docking analysis.
Materials and methods
Results and discussion
Conclusion In the present study, a novel ACEI peptide was identified from casein hydrolysate and successfully characterized by UPLC-Q-TOF-MS/MS. NMAINPSKENLCSTFCK, derived from the αs2-casein fragment of residues 25–41, showed potent ACEI activity with an IC50 value of 129.07 μM and mixed-type inhibition against ACE. One highly possible potential ACE inhibitory mechanism was proposed, in combination with the physicochemical characteristics, secondary structure (CD spectra), and spatial structure of this 17-residue peptide, as well as molecular docking of a hydrolyzed fragment (NMAINPSKE) with ACE. This work indicated that ACEI peptides can be screened by sequence similarity and the degradation of the ACEI peptides should be taken into consideration in the study of ACEI peptides inhibitory mechanisms.
Hypertension which causes heart failure is very common now a day, it has no symptoms, but sometimes hypertension causes symptoms such as headache, shortness of breath, dizziness, and chest pain, palpitations of the heart and nose bleeds. Hypertension is more common in men than women and in people over the age of 65 than in younger persons. Studies also reveal that angiotensin converting enzyme (ACE) inhibitors are very useful in the treatment of hypertension and congestive heart failures, as ACE can inactivate the hypertensive nonapeptide bradykinin. In fact, some 30% of hypertensive patients are unable to reach their blood pressure goals. ACE inhibitors have achieved widespread usage in the treatment of cardiovascular and renal disease; ACE inhibitors decrease systemic vascular resistance without increasing heart rate and promote natriuresis. Anti-hypertensive drugs is most effective at lowering systolic blood pressure (SBP) in elderly patients with previously untreated hypertension and the percentage of patients controlled with single or sequential monotherapy .