1.6-Å Crystal Structure of EntA-im

Abstract

Many Gram-positive bacteria produce ribosomally synthesized antimicrobial peptides, often termed bacteriocins. Genes encoding pediocin-like bacteriocins are generally cotranscribed with or in close vicinity to a gene encoding a cognate immunity protein that protects the bacteriocin-producer from their own bacteriocin. We present the first crystal structure of a pediocin-like immunity protein, EntA-im, conferring immunity to the bacteriocin enterocin A. Determination of the structure of this 103-amino acid protein revealed that it folds into an antiparallel four-helix bundle with a flexible C-terminal part. The fact that the immunity protein conferring immunity to carnobacteriocin B2 also consists of a four-helix bundle (Sprules, T., Kawulka, K. E., and Vederas, J. C. (2004) Biochemistry 43, 11740 -11749) strongly indicates that this is a conserved structural motif in all pediocinlike immunity proteins. The C-terminal half of the immunity protein contains a region that recognizes the C-terminal half of the cognate bacteriocin, and the flexibility in the C-terminal end of the immunity protein might thus be an important characteristic that enables the immunity protein to interact with its cognate bacteriocin. By homology modeling of three other pediocin-like immunity proteins and calculation of the surface charge distribution for EntA-im and the three structure models, different charge distributions were observed. The differences in the latter part of helix 3, the beginning of helix 4, and the loop connecting these helices might also be of importance in determining the specificity.

Anticancer α-Helical Peptides and Structure / Function Relationships Underpinning Their Interactions with Tumour Cell Membranes

“…In turn, this increased affinity leads to the formation of well defined pores using a highly specific mechanism that involves both nisin and lipid II molecules and most recently, a model been proposed to describe this mechanism [143]. A number of other lantibiotics have been reported to target lipid II and permeabilise the membranes of target bacteria [143,144] whilst some class IIa bacteriocins that show specificity for Listeria may also use a receptor-mediated pore-forming mechanism to exert their antibacterial action [145][146][147]. Based on the generally close correspondence between the antimicrobial and anticancer activity of many peptides, a recent study tested nisins for activity against cells of the HL-60 leukaemia cell [116].…”

The structure of pyogenecin immunity protein, a novel bacteriocin-like immunity protein from Streptococcus pyogenes

“…For each class IIa bacteriocin encoded in a genome there is a one to one relationship between bacteriocin and cognate immunity protein; whereas, in contrast, for each pair of class IIb two-peptide bacteriocins there is a single cognate immunity protein encoded in a genome [9]. Structures of five immunity proteins have already been solved: ImB2 [19], EntA-im [20], PedB [21], PisI [22], and Mun-Im [23], all protective against IIa bacteriocins. As yet, no structures for immunity proteins protective against IIb or IIc bacteriocins have been solved.…”

Identification of a bacteriocin and its cognate immunity factor expressed by Moraxella catarrhalis

“…The McbI protein contains only 74 amino acids and did not show a high degree of amino acid sequence homology to other immunity proteins, a result which is not unusual [39]. However, the predicted secondary structure of McbI showed the presence of four α-helices, a feature that is conserved among class IIa immunity proteins [35,41]. Precisely how the immunity protein confers protection against its cognate bacteriocin has been elucidated for at least one class II bacteriocin [42].…”