Histidine protects against zinc and nickel toxicity in Caenorhabditis elegans.
PLoS Genet 2011;
7:e1002013. [PMID:
21455490 PMCID:
PMC3063764 DOI:
10.1371/journal.pgen.1002013]
[Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2010] [Accepted: 01/10/2011] [Indexed: 01/16/2023] Open
Abstract
Zinc is an essential trace element involved in a wide range of biological
processes and human diseases. Zinc excess is deleterious, and animals require
mechanisms to protect against zinc toxicity. To identify genes that modulate
zinc tolerance, we performed a forward genetic screen for Caenorhabditis
elegans mutants that were resistant to zinc toxicity. Here we
demonstrate that mutations of the C. elegans histidine ammonia
lyase (haly-1) gene promote zinc tolerance. C. elegans
haly-1 encodes a protein that is homologous to vertebrate HAL, an
enzyme that converts histidine to urocanic acid. haly-1 mutant
animals displayed elevated levels of histidine, indicating that C.
elegans HALY-1 protein is an enzyme involved in histidine
catabolism. These results suggest the model that elevated histidine chelates
zinc and thereby reduces zinc toxicity. Supporting this hypothesis, we
demonstrated that dietary histidine promotes zinc tolerance. Nickel is another
metal that binds histidine with high affinity. We demonstrated that
haly-1 mutant animals are resistant to nickel toxicity and
dietary histidine promotes nickel tolerance in wild-type animals. These studies
identify a novel role for haly-1 and histidine in zinc
metabolism and may be relevant for other animals.
Zinc is an essential nutrient that is critical for human health. However, excess
zinc can cause toxicity, indicating that regulatory mechanisms are necessary to
maintain homeostasis. The analysis of mechanisms that promote zinc homeostasis
can elucidate fundamental regulatory processes and suggest new approaches for
treating disorders of zinc metabolism. To discover genes that modulate zinc
tolerance, we screened for C. elegans mutants that were
resistant to zinc toxicity. Here we demonstrate that mutations of the histidine
ammonia lyase (haly-1) gene promote zinc tolerance.
haly-1 encodes a protein that is similar to vertebrate HAL,
an enzyme that converts histidine to urocanic acid. Mutations in the human HAL
gene cause elevated levels of serum histidine and abnormal zinc metabolism.
Mutations in C. elegans haly-1 cause elevated levels of
histidine, suggesting that histidine causes resistance to excess zinc.
Consistent with this hypothesis, we demonstrated that dietary histidine promoted
tolerance to excess zinc in wild-type worms. Mutations in
haly-1 and supplemental dietary histidine also caused
resistance to nickel, another metal that can bind histidine. A likely mechanism
of protection is chelation of zinc and nickel by histidine. These studies
suggest that histidine plays a physiological role in zinc metabolism.
Collapse