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Haemophilus somnus possesses two systems for acquisition of transferrin-bound iron.

ABSTRACT: Haemophilus somnus strain 649 was found to acquire iron from ovine, bovine, and goat transferrins (Tfs). Expression of Tf receptors, as evaluated by solid-phase binding assays, required the organisms to be grown under iron-restricted conditions in the presence of Tf. Competition binding assays revealed the presence of two distinct Tf-binding receptor systems, one specific for bovine Tf and the other capable of binding all three ruminant Tfs. Affinity isolation procedures using total membranes yielded three putative bovine Tf-binding polypeptides and one putative ovine and goat Tf-binding polypeptide. PCR amplification followed by DNA sequence analyses revealed that H. somnus strain 649 possesses genes that encode a bipartite TbpA-TbpB receptor along with a homolog of the Histophilus ovis single-component TbpA receptor. Expression of TbpB and the single-component TbpA would appear to be subject to a form of phase variation involving homopolymeric nucleotide tracts within the structural genes.

SUBMITTER: Ekins A

PROVIDER: S-EPMC421612 | biostudies-literature | 2004 Jul

REPOSITORIES: biostudies-literature

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Haemophilus somnus possesses two systems for acquisition of transferrin-bound iron.

Ekins Andrew A Bahrami Fariborz F Sijercic Ada A Maret Deborah D Niven Donald F DF

Journal of bacteriology 20040701 13

Haemophilus somnus strain 649 was found to acquire iron from ovine, bovine, and goat transferrins (Tfs). Expression of Tf receptors, as evaluated by solid-phase binding assays, required the organisms to be grown under iron-restricted conditions in the presence of Tf. Competition binding assays revealed the presence of two distinct Tf-binding receptor systems, one specific for bovine Tf and the other capable of binding all three ruminant Tfs. Affinity isolation procedures using total membranes yi ...[more]

PMID: 15205447

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Project description:The molecular mechanisms of iron trafficking in neurons have not been elucidated. In this study, we characterized the expression and localization of ferrous iron transporters Zip8, Zip14 and divalent metal transporter 1 (DMT1), and ferrireductases Steap2 and stromal cell-derived receptor 2 in primary rat hippocampal neurons. Steap2 and Zip8 partially co-localize, indicating these two proteins may function in Fe(3+) reduction prior to Fe(2+) permeation. Zip8, DMT1, and Steap2 co-localize with the transferrin receptor/transferrin complex, suggesting they may be involved in transferrin receptor/transferrin-mediated iron assimilation. In brain interstitial fluid, transferring-bound iron (TBI) and non-transferrin-bound iron (NTBI) exist as potential iron sources. Primary hippocampal neurons exhibit significant iron uptake from TBI (Transferrin-(59) Fe(3+)) and NTBI, whether presented as (59) Fe(2+) -citrate or (59) Fe(3+) -citrate; reductase-independent (59) Fe(2+) uptake was the most efficient uptake pathway of the three. Kinetic analysis of Zn(2+) inhibition of Fe(2+) uptake indicated that DMT1 plays only a minor role in the uptake of NTBI. In contrast, localization and knockdown data indicate that Zip8 makes a major contribution. Data suggest also that cell accumulation of (59) Fe from TBI relies at least in part on an endocytosis-independent pathway. These data suggest that Zip8 and Steap2 play a major role in iron accumulation from NTBI and TBI by hippocampal neurons. Analysis of the expression and localization of known iron uptake transporters demonstrated that Zip8 makes a major contribution to iron accumulation in primary cultures of rat embryonic hippocampal neurons. These cells exhibit uptake pathways for ferrous and ferric iron (non-transferrin-bound iron, NTBI in figure) and for transferrin-bound iron; the ferrireductases Steap2 and SDR2 support the uptake of ferric iron substrates. Zip8 and Steap2 are strongly expressed in the plasma membrane of both soma and processes, implying a crucial role in iron accumulation from NTBI and transferrin-bound iron (TBI) by hippocampal neurons.

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Haemophilus somnus possesses two systems for acquisition of transferrin-bound iron.

Publications

Haemophilus somnus possesses two systems for acquisition of transferrin-bound iron.

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