Abstract
Multicopper oxidases (MCOs) are enzymes that contain 10 conserved histidine residues and 1 cysteine residue. MCO1 has been extensively investigated in the midgut because this MCO is implicated in ascorbate oxidation, iron homeostasis and immune responses. However, information regarding the action of MCO1 in Malpighian tubules is limited. In this study, Helicoverpa armigera was used as a model to investigate the function of MCO1 in Malpighian tubules. Sequence analysis results revealed that HaMCO1 exhibits typical MCO characteristics, with 10 histidine and 1 cysteine residues for copper ion binding. HaMCO1 was also found to be highly abundant in Malpighian tubules. Temporal expression patterns indicated that HaMCO1 is mainly expressed during larval molting stages. Hormone treatments [the molting hormone 20-hydroxyecdysone (20E) and juvenile hormone (JH)] revealed that 20E inhibits HaMCO1 transcript expression via its heterodimer receptor, which consists of ecdysone receptor (EcR) and ultraspiracle (USP), and that JH counteracts the action of 20E to activate HaMCO1 transcript expression via its intracellular receptor methoprene-tolerant (Met). HaMCO1 knockdown caused a significant decrease in iron accumulation and also significantly reduced transferrin and ferritin transcript expression. Therefore, HaMCO1 is coordinately regulated by 20E and JH and is required for iron homeostasis in Malpighian tubules.
Highlights
Multicopper oxidases (MCOs) are enzymes that contain 10 conserved histidine residues and 1 cysteine residue
HaMCO1 contains an open reading frame (ORF) of 2,430 bp, which encodes a putative protein of 810 amino acid residues, with a molecular weight with 91.998 kDa and an isoelectric point of 5.46 (Fig. 1)
The results revealed that HaMCO1 contains ten histidine residues and one cysteine residue (Fig. 2)
Summary
Multicopper oxidases (MCOs) are enzymes that contain 10 conserved histidine residues and 1 cysteine residue. MCO2 is abundantly expressed in the epidermis, whereas MCO1 is highly expressed in the midgut and Malpighian tubules during feeding stages. This difference indicates that MCO1 may be involved in diet detoxification[4]. The MCO1 ortholog in Drosophila melanogaster, CG3759, is up-regulated upon septic injury[9], and in A. gambiae and M. sexta, MCO1 is rapidly up-regulated in response to bacterial injection[10] These results suggest that MCO1 might participate in the insect immune response. A subsequent study found that D. melanogaster MCO1 is a functional ferroxidase, with RNAi-mediated knockdown of MCO1 causing a decrease in the level of iron accumulation in the midgut[11]. MCO1 in insects is likely involved in diverse functions, including monolignol detoxification, immune response, metal metabolism and redox reaction
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