Immunoglobulin A1 proteases: a structure–function update

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Abstract
IgA1 (immunoglobulin A1) antibodies are the first line of defence against microbial pathogens such as Neisseria meningitidis and Haemophilus influenzae. However, these bacteria secrete a site-specific protease that is capable of cleaving human IgA1 and interacting with other host components. The IgA proteases are released by the type V secretion pathway, which involves translocation through two membranes and an autolytic, post-translational processing step. Results reported recently throw light on the type V secretion pathway and on the roles of the multifunctional IgA protease. The IgA1 protease-recognition sequence is present within the IgA1 hinge region as well as in the variable sequence connecting the IgA1 protease to its translocator domain. Recent results suggest that neisserial IgA1 proteases are capable of cleaving substrates lacking the classical recognition sequence. This review will cover recent advances in the IgA protease field.