Sites in the CH3 Domain of Human IgA1 That Influence Sensitivity to Bacterial IgA1 Proteases

Abstract

The influence of regions, other than the hinge, on the susceptibility of human IgA1 to cleavage by diverse bacterial IgA1 proteases, was examined using IgA1 mutants bearing amino acid deletions, substitutions, and domain swaps. IgA1 lacking the tailpiece retained its susceptibility to cleavage by all of the IgA1 proteases. The domain swap molecule α1α2γ3, in which the CH3 domain of IgA1 was exchanged for that of human IgG1, was resistant to cleavage with the type 1 and 2 serine IgA1 proteases of Neisseria meningitidis, Neisseria gonorrhoeae, and Haemophilus influenzae, but remained sensitive to cleavage with the metallo-IgA1 proteases of Streptococcus pneumoniae, Streptococcus oralis, Streptococcus sanguis, and Streptococcus mitis. Substitution of the IgA1 Cα3 domain motif Pro440-Phe443 into the corresponding position in the Cγ3 domain of α1α2γ3 resulted now in sensitivity to the type 2 IgA1 protease of N. meningitidis, indicating the possible requirement of these amino acids for sensitivity to this protease. For the H. influenzae type 2 protease, resistance of an IgA1 mutant in which the CH3 domain residues 399–409 were exchanged with those from IgG1, but sensitivity of mutant HuBovα3 in which the Cα3 domain of bovine IgA replaces that of human IgA1, suggests that CH3 domain residues Glu403, Gln406, and Thr409 influence sensitivity to this enzyme. Hence, unlike the situation with the metallo-IgA1 proteases of Streptococcus spp., the sensitivity of human IgA1 to cleavage with the serine IgA1 proteases of Neisseria and Haemophilus involves their binding to different sites specifically in the CH3 domain.

Structure and function relationships in IgA

“…The H. influenzae type 2 enzyme, meanwhile, seems to require C 3 residues also implicated in binding to pIgR 70 ( Figure 3d ). The solved X-ray crystal structure of an H. influenzae IgA1 protease is consistent with Fc involvement, and it has been proposed that binding of Fc by the protease may stabilize a conformation in which the IgA1 hinge peptide can access the enzyme ' s active site resulting in cleavage.…”

“…69 For some IgA1 proteases, cleavage of IgA1 requires the presence of critical elements within the Fc region. 67,70 For example, the Neisseria meningitidis type 2 enzyme seems to require Figure 3 Interaction sites on IgA Fc for bacterial proteins that perturb IgA function. One IgA1 Fc heavy chain is shown in light blue, the other in yellow.…”

Immunization with a ZmpB-Based Protein Vaccine Could Protect against Pneumococcal Diseases in Mice

“…S. pneumoniae has two to four zinc metalloproteinases depending on the strains. The best characterized of them is IgA1 protease, which is involved in pneumococcal adherence and colonization, and it could elicit significant protection against fatal pneumococcal pneumonia in mice (2,37). ZmpC has the capacity to cleave human matrix metalloproteinase-9 (MMP-9) and to stimulate syndecan-1 shedding (12,30), while the role of ZmpD in pneumococcal infection still is unknown.…”

Cleavage of IgGs by proteases associated with invasive diseases

“…76 These investigators generated a number of positional variants and deletion mutants to define certain alterations that could confer protease resistance. 77,78 The effects of such changes on IgA function with regard to pathogen removal were not specifically discussed. A related strategy to confer protease resistance to the IgG hinge would likely be hampered by overlap between the protease susceptibility sites and the highly conserved hinge sequences involved in Fcγ receptor and complement recognition.…”