Dataset Information

ABCG2 transports and transfers heme to albumin through its large extracellular loop.

ABSTRACT: ABCG2 is an ATP-binding cassette (ABC) transporter preferentially expressed by immature human hematopoietic progenitors. Due to its role in drug resistance, its expression has been correlated with a protection role against protoporhyrin IX (PPIX) accumulation in stem cells under hypoxic conditions. We show here that zinc mesoporphyrin, a validated fluorescent heme analog, is transported by ABCG2. We also show that the ABCG2 large extracellular loop ECL3 constitutes a porphyrin-binding domain, which strongly interacts with heme, hemin, PPIX, ZnPPIX, CoPPIX, and much less efficiently with pheophorbide a, but not with vitamin B12. K(d) values are in the range 0.5-3.5 ?m, with heme displaying the highest affinity. Nonporphyrin substrates of ABCG2, such as mitoxantrone, doxo/daunorubicin, and riboflavin, do not bind to ECL3. Single-point mutations H583A and C603A inside ECL3 prevent the binding of hemin but hardly affect that of iron-free PPIX. The extracellular location of ECL3 downstream from the transport sites suggests that, after membrane translocation, hemin is transferred to ECL3, which is strategically positioned to release the bound porphyrin to extracellular partners. We show here that human serum albumin could be one of these possible partners as it removes hemin bound to ECL3 and interacts with ABCG2, with a K(d) of about 3 ?m.

SUBMITTER: Desuzinges-Mandon E

PROVIDER: S-EPMC2963377 | biostudies-literature | 2010 Oct

REPOSITORIES: biostudies-literature

ACCESS DATA

Publications

ABCG2 transports and transfers heme to albumin through its large extracellular loop.

Desuzinges-Mandon Elodie E Arnaud Ophélie O Martinez Lorena L Huché Frédéric F Di Pietro Attilio A Falson Pierre P

The Journal of biological chemistry 20100812 43

ABCG2 is an ATP-binding cassette (ABC) transporter preferentially expressed by immature human hematopoietic progenitors. Due to its role in drug resistance, its expression has been correlated with a protection role against protoporhyrin IX (PPIX) accumulation in stem cells under hypoxic conditions. We show here that zinc mesoporphyrin, a validated fluorescent heme analog, is transported by ABCG2. We also show that the ABCG2 large extracellular loop ECL3 constitutes a porphyrin-binding domain, wh ...[more]

PMID: 20705604

Similar Datasets

Project description:Lymphatic filariasis affects nearly 120 million people worldwide and mass preventive chemotherapy is currently used as a strategy to control this infection. This has substantially reduced the incidence of the infection in several parts of the world. However, a prophylactic vaccine would be more effective in preventing future infections and will supplement the mass chemotherapy efforts. Unfortunately, there is no licensed vaccine available currently to prevent this infection. Molecules expressed on the surface of the parasite are potential candidates for vaccine development as they are exposed to the host immune system. In this study we show that the large extracellular loop of tetraspanin (TSP LEL), a protein expressed on the cuticle of Brugia malayi and Wuchereria bancrofti is a potential vaccine candidate. Our results showed that BmTSP LEL is expressed on the surface of B. malayi infective third stage larvae (L3) and sera from human subjects who are putatively immune to lymphatic filariasis carry high titer of IgG1 and IgG3 antibodies against BmTSP LEL and WbTSP LEL. We also showed that these antibodies in the sera of human subjects can participate in the killing of B. malayi L3 in an antibody dependent cell-mediated cytotoxicity mechanism. Vaccination trials in mice showed that close to 64% protection were achieved against challenge infections with B. malayi L3. Immunized animals showed high titer of anti-WbTSP LEL IgG1, IgG2a and IgG2b antibodies in the sera and IFN-? secreting cells in the spleen. Onchocerca volvulus another filarial parasite also expresses TSP LEL. Cross-reactivity studies showed that IgG1 antibody in the sera of endemic normal subjects, recognize OvTSP LEL. Similarly, anti-OvTSP LEL antibodies in the sera of subjects who are immune to O. volvulus were also shown to cross-react with rWbTSP LEL and rBmTSP LEL. These findings thus suggested that rTSP LEL can be developed as a potential vaccine candidate against multiple filarial infections.

Project description:A large portion of biological iron is found in the form of an iron-protoporphyrin IX complex, or heme. In the human host environment, which is exceptionally poor in free iron, heme iron, particularly from hemoglobin, constitutes a major source of iron for invading microbial pathogens. Several fungi were shown to utilize free heme, and Candida albicans, a major opportunistic pathogen, is able both to capture free heme and to extract heme from hemoglobin using a network of extracellular hemophores. Human serum albumin (HSA) is the most abundant host heme-scavenging protein. Tight binding of heme by HSA restricts its toxic chemical reactivity and could diminish its availability as an iron source for pathogenic microbes. We found, however, that rather than inhibiting heme utilization, HSA greatly increases availability of heme as an iron source for C. albicans and other fungi. In contrast, hemopexin, a low-abundance but high-affinity heme-scavenging serum protein, does inhibit heme utilization by C. albicans However, inhibition by hemopexin is mitigated in the presence of HSA. Utilization of albumin-bound heme requires the same hemophore cascade as that which mediates hemoglobin-iron utilization. Accordingly, we found that the C. albicans hemophores are able to extract heme bound to HSA in vitro Since many common drugs are known to bind to HSA, we tested whether they could interfere with heme-iron utilization. We show that utilization of albumin-bound heme by C. albicans can be inhibited by the anti-inflammatory drugs naproxen and salicylic acid.IMPORTANCE Heme constitutes a major iron source for microorganisms and particularly for pathogenic microbes; to overcome the iron scarcity in the animal host, many pathogenic bacteria and fungi have developed systems to extract and take up heme from host proteins such as hemoglobin. Microbial heme uptake mechanisms are usually studied using growth media containing free heme or hemoglobin as a sole iron source. However, the animal host contains heme-scavenging proteins that could prevent this uptake. In the human host in particular, the most abundant serum heme-binding protein is albumin. Surprisingly, however, we found that in the case of fungi of the Candida species family, albumin promoted rather than prevented heme utilization. Albumin thus constitutes a human-specific factor that can affect heme-iron utilization and could serve as target for preventing heme-iron utilization by fungal pathogens. As a proof of principle, we identify two drugs that can inhibit albumin-stimulated heme utilization.

Dataset Information

ABCG2 transports and transfers heme to albumin through its large extracellular loop.

Publications

ABCG2 transports and transfers heme to albumin through its large extracellular loop.

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure

Tweets