Alpha-lactalbumin is a whey protein which is a cheese making industrial residue of high biological value. The antihypertensive capacity of three peptides obtained from the simulated gastrointestinal digestion of alpha-lactalbumin hydrolysates was studied.
Alpha-lactalbumin hydrolysis was performed using Alcalase enzyme and subsequently subjected to a simulated digestion process by using pepsin and pancreatin enzymes to mimic digestion conditions. The peptides were identified from a RP-HPLC fractionation of the digest and subsequent identification by mass spectrometry analysis. Three peptides from alpha-lactalbumin sequence were obtained: IWCKDDQNPH (P1), KFLDDDLTDDIM (P2) and DKFLDDDLTDDIM (P3). The in vitro antihypertensive activity of the peptides was determined by studying the inhibition of angiotensin converting enzyme, with P1 being the only peptide with antihypertensive activity detected by this methodology (IC50=3.91±0.2 mg/mL).
In order to correlate structural (molecular dynamics simulations) and physicochemical properties (charges, hydrophobicity, solvent accessible areas (ASA, ASA+, ASA-, ASAH, ASAP)) with potential mechanisms of antihypertensive capacity in silico methods were performed. The peptides P1, P2 and P3 had a negative global charge and were hydrophilic. After molecular modelling, the peptide structures were submitted to a refinement based on an energy minimization and further molecular dynamics simulation to assess their global size and conformational space. After 50 nanoseconds simulation, the global structures, solvated and immersed in an ionic water solution similar to that of blood, were studied in their ASA´s. Some secondary structure (alpha-helix) was observed in the P1 peptide but in general, all peptides showed an extended folding. Surfaces were charge code colored and in a visual inspection it could be conjectured that all of them exposed the charge, mainly negative charge, to the solvent surface, in agreement with the GRAVY index which was also evaluated.
In conclusion, the structure and amino acid composition of peptide 1 assessed by in silico studies agrees with the antihypertensive activity obtained by the in vitro study.
