Copper-zinc superoxide dismutase of Haemophilus influenzae and H. parainfluenzae

Abstract

Copper-zinc superoxide dismutase ([Cu,Zn]-SOD) is widely found in eukaryotes but has only rarely been identified in bacteria. Here we describe sodC, encoding [Cu,Zn]-SOD in Haemophilus influenzae and H. parainfluenzae, frequent colonists and pathogens of the human respiratory tract. In capsulate H. influenzae, sodC was found in only one division of the bacterial population, and although the protein it encoded was clearly [Cu,Zn]-SOD from its deduced sequence, it lacked enzymatic activity. In H. parainfluenzae, in contrast, active enzyme was synthesized which appeared to be secreted beyond the cytoplasm when the gene was expressed in Escherichia coli minicells. The origin of gene transcription differed between the Haemophilus species, but protein synthesis from cloned genes in vitro was comparable. A C-T transition was found in the H. influenzae sequence compared with the H. parainfluenzae sequence, leading to a histidine, known to be crucial in eukaryotic [Cu,Zn]-SOD for copper ion coordination and so for enzymatic activity, to be changed to tyrosine. This is speculated to be the cause of inactivity of the H. influenzae enzyme. Secreted SODs have only been described in a few bacterial species, and this is the first identification of [Cu,Zn]-SOD in a common human upper respiratory tract colonist. The role of secreted bacterial SODs is unknown, and we speculate that in Haemophilus species the enzyme may confer survival advantage by accelerating dismutation of superoxide of environmental origin to hydrogen peroxide, disruptive to the normal mucociliary clearance process in the host.

Bacterial copper‐ and zinc‐cofactored superoxide dismutase contributes to the pathogenesis of systemic salmonellosis

“…SODs are classified according to the metalloenzyme at their active site. Copper, zinc (Cu,Zn) cofactored SODs were originally thought to be restricted to eukaryotes but have recently been shown to be present in many Gram-negative pathogens, including Brucella abortus (Beck et al, 1990), members of the Haemophilus-Actinobacillus-Pasteurella group, Neisseria meningitidis (Kroll et al, 1991; Escherichia coli (Benov and Fridovich, 1994) and Legionella pneumophila (St John and Steinman, 1996). We have recently shown that Salmonella possesses a [Cu,Zn]-SOD (Canvin et al, 1996).…”

Presence of Copper- and Zinc-Containing Superoxide Dismutase in Commensal Haemophilus haemolyticus Isolates Can Be Used as a Marker To Discriminate Them from Nontypeable H. influenzae Isolates

“…In extensive studies, we have established that capsulated or noncapsulated H. influenzae sensu stricto strains do not produce active CuZnSOD (11,12,14,16). The population of capsulated H. influenzae strains falls into two widely separated phylogenetic divisions, and while strains segregating to phylogenetic division II (some serotype a and b strains and serotype f strains) plus serotype e strains (distantly related to phylogenetic division II) possess the sodC gene, they do not produce active enzyme (11,16), probably due to a mutation that converts an active-site histidine to tyrosine (11). Among a collection of 45 NT H. influenzae isolates (20), characterized by multilocus enzyme electrophoresis, comprising electrophoretic types 11 to 13, 26 to 27, 29 to 32, 35 to 45, 49 to 51, 53 to 55, 57 to 61, and 63 to 76, neither the sodC gene nor the CuZnSOD protein was detected (16).…”

“…Bacterial CuZnSODs are enzymes found in the periplasms of various gram-negative bacteria and, in the case of pathogens, are thought to have a role in the protection of organisms against host defense-derived free-radical-mediated damage (1,2,6,11,12,15,27). In extensive studies, we have established that capsulated or noncapsulated H. influenzae sensu stricto strains do not produce active CuZnSOD (11,12,14,16).…”

“…Strains used as positive controls were H. haemolyticus NCTC 10839, biotype IV cryptic genospecies H. influenzae strain 16N (16), Neisseria meningitidis MC58 (27), and Actinobacillus pleuropneumoniae 4074 ATCC 27088 (12,13,26); H. influenzae Rd (7, 11) was used as the negative control. A. pleuropneumoniae 4074 and Haemophilus isolates were grown in brain heart infusion (BHI) broth supplemented with 1 g/ml NAD and 10 g/ml hemin at 37°C on an orbital shaker (180 rpm) or on BHI agar plates supplemented with Levinthal's base at 37°C in 5% carbon dioxide (11). N. meningitidis was cultured as described previously (27).…”

On the possible roles of N-terminal His-rich domains of Cu,Zn SODs of some Gram-negative bacteria

“…The increasing number of structurally characterized prokaryotic Cu,Zn superoxide dismutases show a considerable structural variability between proteins from different bacteria, therefore individual enzyme variants may exhibit unique properties [3][4][5][6][7][8]. Such species-specific differences include alteration in the quaternary structure [3,4], mutations in the active site ligands [5][6][7], deletion or insertion in the major enzyme loops [6,7], or the introduction of additional domains at the N-or C-terminus of the enzyme [8]. The Cu,Zn SODs from a few Gram-negative bacteria possess histidine-rich N-terminal extensions, which show typical features of high affinity divalent metal binding domains [8].…”