Phase variation of HpuAB and HmbR, two distinct haemoglobin receptors of Neisseria meningitidis DNM2

Abstract

SummaryWe have previously described HpuAB, a two-component receptor that mediates binding to haemoglobin (Hb), haemoglobin±haptoglobin (Hb-Hp) and apo-haptoglobin (Hp). In this communication, we constructed non-polar mutations in the hpuA and hpuB loci to examine the individual roles of HpuA and HpuB. Our results indicate that both HpuA and HpuB are required for the acquisition of Fe from Hb and Hb-Hp. We isolated Hb utilization-positive (Hb) variants of our Hb utilization-negative (HbÀ) hpu mutants at a frequency of 10 À3 and demonstrated that the Hb phenotype resulted from the expression of a second Hb receptor, HmbR. Expression of HmbR in DNM2 was found to be controlled by translational frameshifting involving a polyguanine (G) tract located within the hmbR locus.

Analysis of Haptoglobin and Hemoglobin-Haptoglobin Interactions with theNeisseria meningitidisTonB-Dependent Receptor HpuAB by Flow Cytometry

“…3C). Hence, despite the absolute requirement for HpuA in HpuAB-mediated Fe acquisition (48,69), in the absence of HpuB we did not detect specific involvement of this lipoprotein in binding to any of the seven ligands recognized by HpuAB.…”

“…We have reported data suggesting that HpuA and HpuB physically interact to form a functional receptor complex (51,69). Characterization of isogenic single mutants of HpuA and HpuB suggested that both receptor components are absolutely required for the utilization of Hb or HbHp (48,69).…”

Involvement of genes of genome maintenance in the regulation of phase variation frequencies in Neisseria meningitidis

“…These genes are often referred to as contingency loci . Phase variable expression has been experimentally demonstrated for surface antigens such as opacity proteins, lipopolysaccharides, capsular polysaccharides, pili, haemoglobin receptors, PorA and Opc outer-membrane proteins, a putative protease and the NadA adhesin (de Vries et al, 1996;Jennings et al, 1998Jennings et al, , 1999Hammerschmidt et al, 1996;Jonsson et al, 1991;Lewis et al, 1999;Richardson & Stojiljkovic,1999;van der Ende et al, 2000;Sarkari et al, 1994;Martin et al, 2003). We recently showed that 47 genes were likely to be regulated by such a mechanism in N. meningitidis strain MC58 (Martin et al, 2003).…”

Identification of a conserved Moraxella catarrhalis haemoglobin-utilization protein, MhuA

“…Previous studies have demonstrated that numerous bacteria can utilize haem, Hb and other haemoprotein complexes as both haem and iron sources (Chen et al, 1996;Genco & Dixon, 2001;Lewis et al, 1997Lewis et al, , 1998Lewis et al, , 1999Stojiljkovic et al, 1996;Wandersman & Stojiljkovic, 2000). Multiple different haemoproteinutilization systems, some of which are redundant, have been characterized for pathogenic species of the genera Neisseria, Haemophilus, Escherichia, Shigella, Yersinia, Pseudomonas, Vibrio and Serratia (Morton et al, 1999;Ochsner et al, 2000;Wandersman & Stojiljkovic, 2000).…”

“…The binding of other unidentified proteins to the Hb-agarose column is consistent with previous data obtained by other investigators studying the Hb-binding activity of proteins from various organisms (Archambault et al, 2003;Bracken et al, 1999;Dashper et al, 2000;Lee & Levesque, 1997;Sengupta et al, 1999). Due to the varied haem and iron sources that are present in the human host and the varied degree of receptor specificities for haemoproteins, it is not surprising that multiple receptor systems exist for haem uptake in many bacterial species (Cope et al, 1995Genco & Dixon, 2001;Lewis et al, 1999;Wandersman & Stojiljkovic, 2000). Like these related organisms, other Hb-binding and -utilization proteins are likely to exist for M. catarrhalis, suggesting the possibility of redundant systems.…”