Biglutaminyl-Biliverdin IX Alpha as a Heme Degradation Product in the Dengue Fever Insect-Vector Aedes aegypti

Abstract

Hemoglobin digestion in the midgut of hematophagous animals results in the release of its prosthetic group, heme, which is a pro-oxidant molecule. Heme enzymatic degradation is a protective mechanism that has been described in several organisms, including plants, bacteria, and mammals. This reaction is catalyzed by heme oxygenase and results in formation of carbon monoxide, ferrous ion, and biliverdin IXα. During digestion, a large amount of a green pigment is produced and secreted into the intestinal lumen of A. aegypti adult females. In the case of another blood-sucking insect, the kissing-bug Rhodnius prolixus, we have recently shown that heme degradation involves a complex pathway that generates dicysteinyl-biliverdin IX gamma. The light absorption spectrum of the Aedes purified pigment was similar to biliverdin, but its mobility on a reverse-phase chromatography column suggested a compound less hydrophobic than biliverdin IXα. Structural characterization by ESI-MS revealed that the mosquito pigment is the α isomer of biliverdin bound to two glutamine residues by an amide bond. This biglutaminyl-biliverdin is formed by oxidative cleavage of the heme porphyrin ring followed by two subsequent additions of glutamine residues to the biliverdin IXα. The role of this pathway in the adaptation of this insect vector to a blood-feeding habit is discussed. Keywordsheme; heme oxygenase; biliverdin; detoxification; Aedes aegypti Dengue fever, associated with dengue hemorrhagic fever (DHF), is the most prevalent vectorborne viral disease affecting humans, transmitted mainly by the mosquito Aedes aegypti (1). The ability of A. aegypti females to transmit these viruses from one vertebrate host to another is strictly related to their hematophagous habit. Ingestion of a blood meal triggers intense protein digestion which takes place in the lumen, providing nutrients required for oogenesis (2) but also leading to the release of high amounts of free heme due to host hemoglobin proteolysis. Heme is potentially toxic due to its capacity to promote the generation of reactive oxygen species (ROS) (3). Being an amphiphilic molecule, heme can also insert itself into phospholipid bilayers, leading to destabilization of membrane structure and cell lysis (4). Blood-sucking arthropods present a complex array of heme detoxification and antioxidant mechanisms (5) that allow them to counteract free heme cytotoxicity and adapt to hematophagy. These include heme-binding proteins in the hemolymph of kissing-bugs (6) and ticks (7), high levels of antioxidant enzymes in the midgut of Rhodnius prolixus (8), and aggregation of heme in the midgut of this kissing-bug (9) and ticks (10,11). In A. aegypti, the peritrophic matrix, an extracellular layer that is secreted by the midgut cells and separates the meal from the midgut epithelium, acts as a protective mechanism by binding free heme released during digestion (12). Recently, an Aedes aegypti peritrophin -a protein component of the peritrophic matrix -has been shown to be a heme-binding ...

Effective disposal of nitrogen waste in blood‐fedAedes aegyptimosquitoes requires alanine aminotransferase

“…We also measured the heme concentration from the same excreta, because the amount of heme defecated is an indication of the progress of blood meal digestion (24,25). In agreement with midgut uric acid accumulation, low uric acid amounts were detected in the excreta (Fig.…”

Coculturing of Mosquito‐Microbiome Bacteria Promotes Heme Degradation in Elizabethkingia anophelis

“…Many bacterial HOs have been characterized and the majority are structurally similar to mammalian HOs . Typically, HOs oxidatively cleave heme at the α‐ meso position to afford biliverdin IXα, CO, and Fe 2+ ; however, cleavage has been observed at all four meso positions (Figure A) . HOs as well as heme‐degrading/cytoplasmic heme‐binding (HemS) proteins with no sequence homology to canonical HOs have been reported in multiple species of bacteria.…”

“… A) Example of heme degradation into biliverdin IXα by a heme oxygenase . Cleavage has been observed at the β‐, δ‐, γ‐ meso positions across nature.…”

The impact of metagenomic interplay on the mosquito redox homeostasis

“…In Ae. aegypti , heme oxygenase catalyzes heme degradation [42]. Apparently, multilayer protective mechanisms have evolved in mosquitoes to cope with the massive heme load from a blood meal.…”