Identification of the Aedes aegypti peritrophic matrix protein AeIMUCI as a heme-binding protein.
The gene Aedes aegypti intestinal mucin 1 (AeIMUC1) encodes a putative peritrophic matrix (PM) protein that is expressed in the midgut of mosquito larvae and adults and is upregulated in response to exposure to heavy metals. The AeIMUC1 protein has a predicted secretory signal peptide and three putative chitin-binding domains (CBDs) with an intervening mucin-like domain. Immunofluorescence and immunoelectron microscopy experiments established that AeIMUC1 is a bona fide PM protein, and binding of the recombinant protein to chitin was demonstrated in vitro. Previous experiments suggested that the Ae. aegypti PM can bind toxic heme molecules generated during blood digestion. However, the identity of the binding molecule(s) was unknown. Using of heme-agarose beads and spectrophotometric and microcalorimetric titrations, we show that recombinant AeIMUC1 can bind large amounts of heme in vitro, suggesting for the first time a role for a PM protein in heme detoxification during blood digestion. Binding of heme to AeIMUC1 was accompanied by an altered circular dichroism spectrum indicating a change in protein conformation, consistent with an increase in secondary structure. Heme-binding activity was mapped to the AeIMUC1 CBDs, suggesting that these domains possess dual chitin- and heme-binding activity.
Devenport
Martin
M
Department of Molecular Microbiology and Immunology and Malaria Research Institute, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, Maryland 21205, USA.
Alvarenga
Patricia H
PH
Shao
Li
L
Fujioka
Hisashi
H
Bianconi
M Lucia
ML
Oliveira
Pedro L
PL
Jacobs-Lorena
Marcelo
M
D000330:Aedes / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D002686:Chitin / Q000737:chemistry / Q000378:metabolism*; D002942:Circular Dichroism; D005260:Female; D006418:Heme / Q000737:chemistry / Q000378:metabolism*; D019476:Insect Proteins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000737:chemistry / Q000648:ultrastructure; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D009077:Mucins / Q000032:analysis / Q000737:chemistry / Q000378:metabolism*; D021382:Protein Sorting Signals; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
D019476:Insect Proteins; D009077:Mucins; D021382:Protein Sorting Signals; D011994:Recombinant Proteins; D002686:Chitin; D006418:Heme