PhD ceremony Mr. R. Khusainov: To dehydrate or not. A molecular inquiry into the lantibiotic nisin biosynthesis process

PhD ceremony: Mr. R. Khusainov, 16.15 uur, Academiegebouw, Broerstraat 5, Groningen

Dissertation: To dehydrate or not. A molecular inquiry into the lantibiotic nisin biosynthesis process

Promotor(s): prof. O.P. Kuipers

Faculty: Mathematics and Natural Sciences

Rustem Khusainov studied nisin, the most prominent and the most studied lantibiotic widely applied in more than 50 countries as a safe and natural antibacterial food preservative. Nowadays, many common bacteria have acquired resistance to multiple antibiotics, making some infections virtually impossible to eradicate. Novel antimicrobial agents are therefore needed to combat infections. Lantibiotics form potential class of alternative antibiotics. The thesis of Khusainov provides comprehensive mechanistic insights into the nisin modification enzymes NisB and NisC and their interactions with the substrate, precursor nisin. A pull-down assay is developed in this thesis that allows characterization of NisB and NisC mutants for their specific interactions with precursor nisin. Besides, the data from his study show that NisB modifies precursor nisin in an N-to-C-terminal direction, while an alternating mode of action between NisB and NisC is applied. Extensive site directed mutagenesis of NisB has led to the first model for Ser/Thr dehydration for class I lantibiotic dehydratases and to the conclusion that NisB amino acid residues Y80 and H961 are involved in direct catalysis. Additionally, Khusainov shows that the nisin leader is not absolutely necessary for class I lantibiotic biosynthesis in vivo. However, addition of the leader in trans increases the efficiency of modification. Furthermore, Khusainov identifies regions in the nisin leader important for the interactions with the nisin modification enzymes NisB and NisC as well as for the posttranslational modifications of precursor nisin, whereas and he demonstrates that modifiable residues in the core peptide part of precursor nisin are not involved in direct binding to the nisin modification enzymes NisB and NisC. The results contribute significantly to the understanding of nisin biosynthesis and may ultimately be of benefit for the development of novel extensively modified lantibiotics, which could replace conventional antibiotics in our fight with multi-drug resistant bacteria.