Functional Significance of the E Loop, a Novel Motif Conserved in the Lantibiotic Immunity ATP-Binding Cassette Transport Systems

Abstract

Lantibiotics are peptide-derived antibacterial substances produced by some Gram-positive bacteria and characterized by the presence of unusual amino acids, like lanthionines and dehydrated amino acids. Because lantibiotic producers may be attacked by self-produced lantibiotics, they express immunity proteins on the cytoplasmic membrane. An ATP-binding cassette (ABC) transport system mediated by the LanFEG protein complex is a major system in lantibiotic immunity. Multiple-sequence alignment analysis revealed that LanF proteins contain the E loop, a variant of the Q loop, which is a well-conserved motif in the nucleotide-binding domains (NBDs) of general ABC transporters. To elucidate E loop function, we introduced a mutation in the NukF protein, which is involved in the nukacin-ISK-1 immunity system. Amino acid replacement of glutamic acid in the E loop with glutamine (E85Q) resulted in slight decreases in the immunity level and transport activity. Additionally, the E85A mutation severely impaired the immunity level and transport activity. On the other hand, ATPase activities of purified E85Q and E85A mutants were almost similar to that of the wild type. These results suggested that the E loop found in ABC transporters involved in lantibiotic immunity plays a significant role in the function of these transporters, especially in the structural change of transmembrane domains.

Characterization of the Antimicrobial Peptide Penisin, a Class Ia Novel Lantibiotic from Paenibacillus sp. Strain A3

“…While penB is responsible for dehydration of serine and threonine residues, the cyclase (penC) catalyzes the nucleophilic attack of a cysteine on the dehydrated residues. A dedicated lantibiotic ABC transporter gene (penT), which is required for the export of penisin, was also encoded with highly conserved domains such as Walker A (401-GRNGSGKTT-409), Q-loop (445-VVFQDFV-452), signature sequence (510-SGGQW QR-517), Walker B (529-LYVLDE-535), and H-loop (564-SHR-567), as described in the literature (36). Further, the genome also harbors an additional lantibiotic dehydratase gene similar to penD, which is unusual for the penisin gene cluster.…”

“…In our annotation and analysis, we found a penC gene with 92% similarity to the LanC-like protein of P. elgii B69 with all conserved domains. Unlike paenicidin A, the ABC transporter present in the biosynthetic cluster of penisin is presumed to be involved in both transportation and immunity, as observed for other lantibiotics (36). To confirm the formation of the thioether bond between cysteine amino acids present in penisin, we performed PEGylation experiments with native and reduced forms of the peptide.…”

SmbFT, a Putative ABC Transporter Complex, Confers Protection against the Lantibiotic Smb in Streptococci

“…SmbT encodes permease component and is 238 residues long with six transmembrane domains. SmbF, on the other hand, encodes a 274 residues long protein with ATPase signature sequences (52). The promoter for smb locus lies ϳ3.0 kb upstream of the smbFT genes.…”

“…Several recent studies suggest that, unlike general ABC transporters that transport substrates across the membranes, the ABC transporters related to immunity function transport specific lantibiotics from the membrane to the extracellular space (28,29,55). A recent study identified the presence of a conserved motif, termed the E-loop, in the ABC transporters belonging to LanFEG and BcrAB families (52). This E-loop structure plays an important role in the function of these transporters and perhaps induces structural changes in the transmembrane domains.…”

Cloning and Analysis of the Planosporicin Lantibiotic Biosynthetic Gene Cluster of Planomonospora alba

“…In at least some lantibiotic transporters, the E-loop is necessary for immunity toward the produced compound. In NukF of Staphylococcus warneri ISK-1, E85Q and E85A substitutions in the E loop impaired immunity to nukacin ISK-1, while ATPase activity remained at wild-type (WT) levels (46). Both PspT and PspZ contain a Q-loop, while PspF contains an E-loop.…”