Cleavage of the Human Immunoglobulin A1 (IgA1) Hinge Region by IgA1 Proteases Requires Structures in the Fc region of IgA

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.

Section: Discussionsupporting

confidence: 92%

mentioning

confidence: 99%

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

Senior

Woof

2006

“…This would appear to be in keeping with the proposal that amino acid sequences or structures outside the hinge and Cterminal to it may also be influential in determining the sensitivity of the molecule to cleavage by IgA1 proteases (28).…”

Section: Cleavage By Iga1 Proteases Of Haemophilus and Neisseriasupporting

confidence: 71%

“…A necessary requirement, although not the only one (28), for IgA sensitivity to cleavage by an IgA1 protease is the presence of a suitable amino acid sequence in the hinge. The only known IgA molecules to contain such a hinge sequence are the IgA1 isotypes of human, chimpanzee, and gorilla and the IgA of the orangutan (18).…”

Section: Discussionmentioning

confidence: 99%

The Influences of Hinge Length and Composition on the Susceptibility of Human IgA to Cleavage by Diverse Bacterial IgA1 Proteases

Senior

Woof

2005

The influences of IgA hinge length and composition on its susceptibility to cleavage by bacterial IgA1 proteases were examined using a panel of IgA hinge mutants. The IgA1 proteases of Streptococcus pneumoniae, Streptococcus sanguis strains SK4 and SK49, Neisseria meningitidis, Neisseria gonorrhoeae, and Haemophilus influenzae cleaved IgA2-IgA1 half hinge, an Ab featuring half of the IgA1 hinge incorporated into the equivalent site in IgA1 protease-resistant IgA2, whereas those of Streptococcus mitis, Streptococcus oralis, and S. sanguis strain SK1 did not. Hinge length reduction by removal of two of the four C-terminal proline residues rendered IgA2-IgA1 half hinge resistant to all streptococcal IgA1 metalloproteinases but it remained sensitive to cleavage by the serine-type IgA1 proteases of Neisseria and Haemophilus spp. The four C-terminal proline residues could be substituted by alanine residues or transferred to the N-terminal extremity of the hinge without affect on the susceptibility of the Ab to cleavage by serine-type IgA1 proteases. However, their removal rendered the Ab resistant to cleavage by all the IgA1 proteases. We conclude that the serine-type IgA1 proteases of Neisseria and Haemophilus require the Fab and Fc regions to be separated by at least ten (or in the case of N. gonorrhoeae type I protease, nine) amino acids between Val222 and Cys241 (IgA1 numbering) for efficient access and cleavage. By contrast, the streptococcal IgA1 metalloproteinases require 12 or more appropriate amino acids between the Fab and Fc to maintain a minimum critical distance between the scissile bond and the start of the Fc.

“…The same substitutions (RG) are also present in IgA1 from chimpanzee, which is cut (36). Possibly the position itself could be important, but a human IgA2m (2) is also cut here despite a truncated hinge (37). IgA cleavage sites must be presented to bacterial proteases in the context of the larger IgA molecule for efficient digestion.…”

Section: Sequencing Of Nhp Ighamentioning

confidence: 99%

Nonhuman Primate IgA: Genetic Heterogeneity and Interactions with CD89

Rogers

Jayashankar

Scinicariello

et al. 2008

Nonhuman primates are extremely valuable animal models for a variety of human diseases. However, it is now becoming evident that these models, although widely used, are still uncharacterized. The major role that nonhuman primate species play in AIDS research as well as in the testing of Ab-based therapeutics requires the full characterization of structure and function of their Ab molecules. IgA is the Ab class mostly involved in protection at mucosal surfaces. By binding to its specific Fc receptor CD89, IgA plays additional and poorly understood roles in immunity. Therefore, Ig heavy α (IGHA) constant (C) genes were cloned and sequenced in four different species (rhesus macaques, pig-tailed macaques, baboons, and sooty mangabeys). Sequence analysis confirmed the high degree of intraspecies polymorphism present in nonhuman primates. Individual animals were either homozygous or heterozygous for IGHA genes. Highly variable hinge regions were shared by animals of different geographic origins and were present in different combinations in heterozygous animals. Therefore, it appears that although highly heterogeneous, hinge sequences are present only in limited numbers in various nonhuman primate populations. A macaque recombinant IgA molecule was generated and used to assess its interaction with a recombinant macaque CD89. Macaque CD89 was able to bind its native ligand as well as human IgA1 and IgA2. Presence of Ag enhanced macaque IgA binding and blocking of macaque CD89 N-glycosylation reduced CD89 expression. Together, our results suggest that, despite the presence of IgA polymorphism, nonhuman primates appear suitable for studies that involve the IgA/CD89 system.