Molecular characterization of hpuAB, the hemaglobin-haptoglobin-utilization operon of Neisseria meningitidis
Lisa A. Lewis, Elizabeth Gray, Ying-Ping Wang, Bruce A. Roe, David Dyer
02/14/2011
We previously identified HpuB, an 85 kDa Fe-repressible protein required for utilization of Fe from, and binding to, haemoglobin and the haemoglobin - haptoglobin complex. The gene for hpuB was cloned from Neisseria meningitidis strain DNM2 and the predicted amino acid sequence indicates that HpuB is an outer membrane receptor belonging to the TonB family of high-affinity transport proteins. A second open reading frame predicted to encode a 34.8 kDa lipoprotein was discovered 5' to hpuB, and was designated hpuA. HpuA was identified in a total-membrane-protein preparation by construction of a mutant lacking HpuA. Acylation of HpuA was confirmed by [3H]-palmitic acid labelling of meningococci. Consensus promoter sequences were not apparent 5; to hpuB. The hpuA inserton mutation exerted a polar effect, abolishing expression of hpuB, suggesting that hpuA and hpuB are co-transcribed. The 3.5 kb polycestronic hpuAB mRNA was identified and shown to be transcriptionally repressed by iron. The transcriptional start site was identified 33 nucleotides 5' to the hpuA translational start site, appropriately positioned around consensus promoter and ferric uptake regulator (Fur) - box sequences. The stucture of this operon suggests that HpuA-HpuB is a two-component receptor analoguous to the bipartite transferring receptor TbpB-TbpA.