Molecular characterization of hpuAB, the haemoglobin-haptoglobin-utilization operon of Neisseria meningitidis.
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 insertion mutation exerted a polar effect, abolishing expression of hpuB, suggesting that hpuA and hpuB are co-transcribed. The 3.5 kb polycistronic 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 structure of this operon suggests that HpuA-HpuB is a two-component receptor analogous to the bipartite transferrin receptor TbpB-TbpA.
Lewis
L A
LA
Department of Microbiology and Immunology, State University of New York at Buffalo 14214, USA. llewis@rex.uokhsc.edu
Gray
E
E
Wang
Y P
YP
Roe
B A
BA
Dyer
D W
DW
D000595:Amino Acid Sequence; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D001693:Biological Transport, Active; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D006242:Haptoglobins / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D007501:Iron / Q000378:metabolism; D033862:Iron-Binding Proteins; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009345:Neisseria meningitidis / Q000235:genetics* / Q000378:metabolism*; D009876:Operon; D011990:Receptors, Transferrin / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D033863:Transferrin-Binding Proteins
D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D017931:DNA Primers; D004269:DNA, Bacterial; D006242:Haptoglobins; D006454:Hemoglobins; C105625:HpuB protein, Neisseria; D033862:Iron-Binding Proteins; D008565:Membrane Proteins; D011990:Receptors, Transferrin; D033863:Transferrin-Binding Proteins; C057616:tonB protein, Bacteria; D007501:Iron