Effect of lactosylation on plasmin-induced hydrolysis of β-casein.

The inhibition of the plasmin-induced hydrolysis of β-casein was explored by decreasing β-casein availability through lactosylation. As plasmin hydrolyses proteins on the carboxyl site of lysine and arginine residues, with a preference for lysine, the lysine residues on the β-casein backbone were targeted. The results indicated that modification of lysine affects plasmin-induced hydrolysis negatively in proportion to the increase in the lactosylation level and independent of the stages of the Maillard reaction. Early stages of the Maillard reaction, e.g., lactosylation, involve the attachment of lactose at the ε-amino group of lysine and advanced stages involve cross-linking, thus modifying lysine and making it unrecognisable to plasmin; in addition, the cross-linking may affect the release of plasmin-generated peptides. These results indicate that lactosylation can be used to control the plasmin-induced hydrolysis of milk proteins and the mechanism can be useful for generating a plasmin-resistant protein using different methods of protein modification

Bio-inspired network optimization in soft materials — Insights from the plant cell wall

The dynamic-mechanical responses of ionotropic gels made from the biopolymer pectin have recently been investigated by microrheological experiments and found to exhibit behaviour indicative of semi-flexible polymer networks. In this work we investigate the gelling behaviour of pectin systems in which an enzyme (pectinmethylesterase, PME) is used to liberate ion-binding sites on initially inert polymers, while in the presence of ions. This is in contrast to the previous work, where it was the release of ions (rather than ion-binding groups) that was controlled and the polymers had pre-existing cross-linkable moieties. In stark contrast to the semi-flexible network paradigm of biological gels and the previous work on pectin, the gels studied herein exhibit the properties of chemically cross-linked networks of flexible polymers