Format

Send to

Choose Destination
J Bacteriol. 2004 Jul;186(13):4067-74.

Free and hemophore-bound heme acquisitions through the outer membrane receptor HasR have different requirements for the TonB-ExbB-ExbD complex.

Author information

1
Unité des Membranes Bactériennes, Institut Pasteur (CNRS URA2172), 75724 Paris 15, France.

Abstract

Many gram-negative bacteria have specific outer membrane receptors for free heme, hemoproteins, and hemophores. Heme is a major iron source and is taken up intact, whereas hemoproteins and hemophores are not transported: the iron-containing molecule has to be stripped off at the cell surface, with only the heme moiety being taken up. The Serratia marcescens hemophore-specific outer membrane receptor HasR can transport either heme itself or heme bound to the hemophore HasA. This second mechanism is much more efficient and requires a higher TonB-ExbB-ExbD (TonB complex) concentration than does free or hemoglobin-bound heme uptake. This requirement for more of the TonB complex is associated with a higher energy requirement. Indeed, the sensitivity of heme-hemophore uptake to the protonophore carbonyl cyanide m-chlorophenyl hydrazone is higher than that of heme uptake from hemoglobin. We show that a higher TonB complex concentration is required for hemophore dissociation from the receptor. This dissociation is concomitant with heme uptake. We propose that increasing the TonB complex concentration drives more energy to the outer membrane receptor and speeds up the release of empty hemophores, which, if they remained on receptors, would inhibit heme transport.

PMID:
15205408
PMCID:
PMC421607
DOI:
10.1128/JB.186.13.4067-4074.2004
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center