Variable processing of the IgA protease autotransporter at the cell surface of Neisseria meningitidis

Abstract

As with all classical monomeric autotransporters, IgA protease of Neisseria meningitidis is a modular protein consisting of an N-terminal signal sequence, a passenger domain and a Cterminal translocator domain (TD) that assists in the secretion of the passenger domain across the outer membrane. The passenger of IgA protease consists of three separate domains: the protease domain, the c-peptide and the a-peptide that contains nuclear localization signals (NLSs). The protease domain is released into the extracellular milieu either via autocatalytic processing or via cleavage by another autotransporter, NalP, expression of which is phase-variable. NalP-mediated cleavage results in the release of a passenger that includes the a-and c-peptides. Here, we studied the fate of the a-peptide when NalP was not expressed and observed strain-dependent differences. In meningococcal strains where the a-peptide contained a single NLS, the a-peptide remained covalently attached to the TD and was detected at the cell surface. In other strains, the a-peptide contained four NLSs and was separated from the TD by an IgA protease autoproteolytic cleavage site. In many of those cases, the a-peptide was found non-covalently associated with the cells as a separate polypeptide. The cell surface association of the a-peptides may be relevant physiologically. We report a novel function for the a-peptide, i.e. the binding of heparin -an immune-modulatory molecule that in the host is found in the extracellular matrix and connected to cell surfaces.

Expression of the Gene for Autotransporter AutB of Neisseria meningitidis Affects Biofilm Formation and Epithelial Transmigration

“…The expected 73-kDa band was detected in cell-envelope preparations but no band reacting with the antiserum was detected in supernatant preparations (Figure 5A). As a control, the secretion of IgA protease was also analyzed using specific antibodies against its translocator domain and the α-peptide, which is released into the milieu after cleavage by NalP (Roussel-Jazédé et al, 2014). As expected, the translocator domain and the α-peptide were detected in the cell envelope fraction and the culture supernatant, respectively (Figure 5A).…”

“…This role would be equivalent to those of NHBA and the α-peptide of IgA protease (Arenas et al, 2013a). Although the expression of the genes for NHBA and IgA protease has not been reported to be phase variable, these proteins are cleaved from the cell surface by the AT protease NalP (Serruto et al, 2003; van Ulsen et al, 2003; Roussel-Jazédé et al, 2014), the expression of which is phase variable (Saunders et al, 2000). Thus, AutB may serve as a backup mechanism that enables biofilm formation if the amount of cell-surface-exposed NHBA and α-peptide is low.…”

“…The monoclonal antibody MN2D6D directed against RmpM and the antiserum directed against fHbp were generously provided by the Netherlands Vaccine Institute (Bilthoven, The Netherlands) and by GlaxoSmithKline (Rixensart, Belgium), respectively. The antisera directed against the α-peptide and the translocator domain of IgA protease were from our laboratory collection (Roussel-Jazédé et al, 2014). …”

Interstrain Cooperation in Meningococcal Biofilms: Role of Autotransporters NalP and AutA

“…The passenger of IgA protease consists of two separate domains, the protease domain and the α-peptide, which are connected via a small γ-peptide (Pohlner et al, 1987). The protease domain is released into the extracellular milieu via autocatalytic processing (Pohlner et al, 1987), but it may also be released connected to the α-peptide after cleavage by NalP (van Ulsen et al, 2003; Roussel-Jazédé et al, 2014). …”

“…In the absence of NalP, the α-peptide of IgA protease (αP) usually remains attached at the cell-surface (Roussel-Jazédé et al, 2014). This αP contains nuclear localization signals, which are positively charged, arginine-rich peptide segments (Pohlner et al, 1995) that bind eDNA and therefore, when present at the cell surface, they increase initiation of biofilm formation.…”