Transglutaminase-mediated crosslinking of a host defence peptide derived from human apolipoprotein B and its effect on the peptide antimicrobial activity.

Background Microbial transglutaminase (mTG) has been successfully used to produce site-specific protein conjugates derivatized at the level of Gln and/or Lys residues for different biotechnological applications. Here, a recombinant peptide identified in human apolipoprotein B sequence, named r(P)ApoB and endowed with antimicrobial activity, was studied as a possible acyl acceptor substrate of mTG with at least one of the six Lys residues present in its sequence. Methods The enzymatic crosslinking reaction was performed in vitro using N,N-dimethylcasein, substance P and bitter vetch (Vicia ervilia) seed proteins, well known acyl donor substrates in mTG-catalyzed reactions. Mass spectrometry analyses were performed for identifying the Lys residue(s) involved in the crosslinking reaction. Finally, bitter vetch protein-based antimicrobial films grafted with r(P)ApoB were prepared and, their biological activity evaluated. Results r(P)ApoB was able to be enzymatically modified by mTG. In particular, it was demonstrated the highly selective crosslinking of the peptide under study by mTG at level of Lys-18. Interestingly, the biological activity of the peptide when grafted into protein-based films was found to be lost following mTG-catalyzed crosslinking. Conclusions r(P)ApoB was shown to be an effective acyl acceptor substrate of mTG. The involvement of Lys-18 in the enzymatic reaction was demonstrated. In addition, films grafted with r(P)ApoB in the presence of mTG lost antimicrobial property. General significance A possible role of mTG as biotechnological tool to modulate the r(P)ApoB antimicrobial activity was hypothesized, and a potential use in food packaging of protein-based films grafted with r(P)ApoB was suggested.