Proteases from Schistosoma mansoni cercariae cleave IgE at solvent exposed interdomain regions.
Parasitic infections, including schistosomiasis, are associated with high titres of specific and non-specific IgE antibody, and many reports show an in vitro role for IgE in parasite killing. Despite an active immune response, schistosomes survive for long periods in the human bloodstream, implying that the parasite is able to overcome or evade the IgE response mounted against it. One such mechanism is through cleavage of IgE into non-functional fragments by potent parasite derived enzymes. Using domain swap antibodies, recombinant Fcepsilon, and C-terminally tagged Cepsilon4 domains, we have narrowed down the principal cleavage sites to the Cepsilon2/Cepsilon3 and Cepsilon3/Cepsilon4 interdomain region of the IgE-Fc. Two serine proteases, one chymotrypsin-like and the second trypsin-like, have been proposed to be involved. Inhibition assays using selective inhibitors confirmed that both proteases contribute to Fc cleavage, although the chymotrypsin-like enzyme makes the greater contribution. Protein sequencing of IgE fragments cleaved by highly pure preparations of the chymotrypsin-like enzyme revealed that cleavage also occurred post Lys residues within kappa light chain dimers (LELK/GA). Related sequences are found in myosin, thrombospondin, collagen and actin-related proteins; macromolecules present in the skin and through which cercariae must penetrate to initiate an infection. Chemical knockout experiments using specific inhibitors and chromogenic substrates allowed us to show that the trypsin-like enzyme was responsible for light chain cleavage. The finding that pathogenic proteases can cleave the Fc of IgE may provide a useful biochemical tool for the further analysis of IgE structure. Indeed, the finding may raise new possibilities for treatment of IgE-mediated allergic reactions mediated through Fcepsilon-receptors.
Aslam
Akhmed
A
Institute of Genetics, University of Nottingham, Queen's Medical Centre, Nottingham, UK. akhmed.aslam@nottingham.ac.uk
Quinn
Phyllis
P
McIntosh
Richard S
RS
Shi
Jianguo
J
Ghumra
Ashfaq
A
McKerrow
James H
JH
Bunting
Karen A
KA
Dunne
David W
DW
Doenhoff
Michael J
MJ
Morrison
Sherie L
SL
Zhang
Ke
K
Pleass
Richard J
RJ
D000595:Amino Acid Sequence; D000818:Animals; D000906:Antibodies; D001536:Bence Jones Protein / Q000378:metabolism; D019295:Computational Biology; D019281:Dimerization; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007073:Immunoglobulin E / Q000737:chemistry* / Q000378:metabolism*; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010196:Pancreatic Elastase / Q000302:isolation & purification / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D051381:Rats; D011994:Recombinant Proteins / Q000302:isolation & purification / Q000378:metabolism; D012550:Schistosoma mansoni / Q000187:drug effects / Q000201:enzymology*; D012997:Solvents / Q000378:metabolism*; D013379:Substrate Specificity / Q000187:drug effects
D000906:Antibodies; D004791:Enzyme Inhibitors; D011994:Recombinant Proteins; D012997:Solvents; D007073:Immunoglobulin E; D001536:Bence Jones Protein; D010196:Pancreatic Elastase