In:
Eukaryotic Cell, American Society for Microbiology, Vol. 13, No. 2 ( 2014-02), p. 231-239
Abstract:
The anaerobic intestinal pathogen Giardia intestinalis does not possess enzymes for heme synthesis, and it also lacks the typical set of hemoproteins that are involved in mitochondrial respiration and cellular oxygen stress management. Nevertheless, G. intestinalis may require heme for the function of particular hemoproteins, such as cytochrome b 5 (cyt b 5 ). We have analyzed the sequences of eukaryotic cyt b 5 proteins and identified three distinct cyt b 5 groups: group I, which consists of C-tail membrane-anchored cyt b 5 proteins; group II, which includes soluble cyt b 5 proteins; and group III, which comprises the fungal cyt b 5 proteins. The majority of eukaryotes possess both group I and II cyt b 5 proteins, whereas three Giardia paralogs belong to group II. We have identified a fourth Giardia cyt b 5 paralog (gCYTb5-IV) that is rather divergent and possesses an unusual 134-residue N-terminal extension. Recombinant Giardia cyt b 5 proteins, including gCYTb5-IV, were expressed in Escherichia coli and exhibited characteristic UV-visible spectra that corresponded to heme-loaded cyt b 5 proteins. The expression of the recombinant gCYTb5-IV in G. intestinalis resulted in the increased import of extracellular heme and its incorporation into the protein, whereas this effect was not observed when gCYTb5-IV containing a mutated heme-binding site was expressed. The electrons for Giardia cyt b 5 proteins may be provided by the NADPH-dependent Tah18-like oxidoreductase GiOR-1. Therefore, GiOR-1 and cyt b 5 may constitute a novel redox system in G. intestinalis . To our knowledge, G. intestinalis is the first anaerobic eukaryote in which the presence of heme has been directly demonstrated.
Type of Medium:
Online Resource
ISSN:
1535-9778
,
1535-9786
Language:
English
Publisher:
American Society for Microbiology
Publication Date:
2014
detail.hit.zdb_id:
2071564-X
SSG:
12
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