Structural Basis for the Inhibition of Human Lysozyme by PliC from Brucella abortus

Abstract

Lysozymes are the first line of defense for a diverse range of organisms that catalyze the degradation of bacterial peptidoglycan. Gram-negative bacteria produce proteinaceous lysozyme inhibitors to protect themselves from the action of lysozymes. To date, MliC or PliC (membrane-bound or periplasmic inhibitor of c-type lysozyme, respectively) has been found in various Gram-negative bacteria. Here, we report the crystal structures of Brucella abortus PliC and its complex with human c-type lysozyme. The complex structure demonstrates that the invariant loop of MliC/PliC plays a crucial role in the inhibition of lysozyme via its insertion into the active site cleft of the lysozyme, as previously observed in the complex structure of Pseudomonas aeruginosa MliC and chicken c-type lysozyme. We identified a new binding interface between a loop adjacent to the active site of human lysozyme and a loop carrying Glu112 of B. abortus PliC, the structure of which was disordered in P. aeruginosa MliC. Because MliC/PliC family members have been implicated as putative colonization or virulence factors, the structures and mechanism of action of MliC/PliC will be relevant to the control of bacterial growth in animal hosts.

A Moraxella catarrhalis Two-Component Signal Transduction System Necessary for Growth in Liquid Media Affects Production of Two Lysozyme Inhibitors

“…This is because the B. abortus PliC protein and LipA may specifically inhibit human lysozyme. A cocrystal structure revealed the residues that are important for the B. abortus PliC protein to contact human lysozyme (68). Our alignments suggest that only 1 or 2 of these residues is conserved between the M. catarrhalis proteins and this B. abortus protein.…”

“…S. Typhimurium PliC residues homologous to those known to contact hen egg white lysozyme in the P. aeruginosa MliC-hen egg white lysozyme structure (66) are boxed. Also shown in boxes are residues from B. abortus PliC that contact human lysozyme in that complex structure (68). The two absolutely conserved cysteines are highlighted in yellow, and the absolutely conserved serine is highlighted in blue.…”

Edwardsiella tarda MliC, a Lysozyme Inhibitor That Participates in Pathogenesis in a Manner That Parallels Ivy

“…Lysozyme-inhibitory activity of rMliC. Since lysozyme inhibitors in their natural forms are usually difficult to obtain, especially with relatively high purity, these proteins have been studied in the form of recombinant proteins (13,17,20,21,32). In our study, to examine the biological activity of MliC Et , rMliC was purified from E. coli as a Trx-tagged protein.…”

“…These inhibitors are known as inhibitor of vertebrate lysozyme (Ivy) proteins, which target C-type lysozyme, periplasmic lysozyme inhibitor of C-type lysozyme (PliC), membrane-associated lysozyme inhibitor of Ctype lysozyme (MliC), periplasmic inhibitor of I-type lysozyme (PliI), and periplasmic inhibitor of G-type lysozyme (PliG) (13)(14)(15)(16)(17). Of these inhibitors, MliC/PliC have been found in various bacterial species, and high-resolution structures of the MliCs/ PliCs of Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica serovar Typhimurium, and Brucella abortus have been reported (18)(19)(20)(21). It seems that MliC proteins fall into two subgroups, which differ in dimer formation.…”

“…It seems that MliC proteins fall into two subgroups, which differ in dimer formation. Subgroup 1 is represented by the E. coli MliC (MliC Ec ), which exists as a monomer in solution (18), while subgroup 2, which includes P. aeruginosa MliC (MliC Pa ) and B. abortus PliC, appear to be dimeric proteins in their crystal structures (19,21).…”