Abstract
Lantibiotics are potent antimicrobial peptides. Nisin is the most prominent member and contains five crucial lanthionine rings. Some clinically relevant bacteria express membrane-associated resistance proteins that proteolytically inactivate nisin. However, substrate recognition and specificity of these proteins is unknown. Here, we report the first three-dimensional structure of a nisin resistance protein from Streptococcus agalactiae (SaNSR) at 2.2 Å resolution. It contains an N-terminal helical bundle, and protease cap and core domains. The latter harbors the highly conserved TASSAEM region, which lies in a hydrophobic tunnel formed by all domains. By integrative modeling, mutagenesis studies, and genetic engineering of nisin variants, a model of the SaNSR/nisin complex is generated, revealing that SaNSR recognizes the last C-terminally located lanthionine ring of nisin. This determines the substrate specificity of SaNSR and ensures the exact coordination of the nisin cleavage site at the TASSAEM region.
Highlights
Mechanisms such as cell wall modifications, biofilm formation or the expression of resistance proteins[18]
Mutagenesis studies guided by molecular dynamics (MD) simulations reveal that SaNSR recognizes the lanthionine ring closest to the C- terminus of nisin and that this ring binds at one end of the catalytic tunnel, thereby determining the substrate specificity and ensuring the exact coordination of the nisin cleavage site at the catalytic site region
A dynamic helical region is present at the N-termini of staphylococcal complement inhibitors (SCINs) (Z-score of 4.7), which is responsible for binding to the substrate C3b and is necessary for the formation of higher order complexes of C3b, which blocks phagocytosis[36]. While these findings suggest that a certain degree of mobility of the found helical bundles is required for function, in three replicates of molecular dynamics (MD) simulations of a monomer of SaNSR
Summary
Mechanisms such as cell wall modifications, biofilm formation or the expression of resistance proteins[18]. For the latter case, a nsr gene was identified in the Streptococcus lactis subspecies diacetylactis (DRC3) that encodes the nisin resistance protein, NSR17,19. The NSR protein from S. agalactiae ATCC 13813 induced a 20-fold increased resistance towards nisin when expressed in L. lactis[22]. NSR is localized within an operon comprising five genes, which encode for NSR, a two-component signaling system (NsrRK), and an ABC transporter (NsrFP) When expressed together, these proteins deliver full nisin resistance[22]. We report the first structure of a nisin resistance protein, NSR from S. agalactiae COH1 (SaNSR). Mutagenesis studies guided by molecular dynamics (MD) simulations reveal that SaNSR recognizes the lanthionine ring closest to the C- terminus of nisin and that this ring binds at one end of the catalytic tunnel, thereby determining the substrate specificity and ensuring the exact coordination of the nisin cleavage site at the catalytic site region
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