Typing and surface charges of the variable loop regions of PorB from Neisseria meningitidis

Abstract

PorB is a pan-Neisserial major outer membrane protein with a trimeric b-barrel structure. Each monomer presents eight periplasmic turns and eight surface exposed loop regions with sequence variability. PorB induces activation of host cell responses via a TLR2-dependent mechanism likely mediated by electrostatic interactions between TLR2 and PorB surface exposed loops. Variability in the loop amino acid sequence is known to influence cell responses to PorB in vitro, particularly for the residues in L5 and L7. In this work, the sequence of the porB gene and the electrostatic surface charges of PorB from 35 invasive meningococcal isolates belonging to the main clonal complexes identified in Italy and from five carriage genomes available on the website http://pubmlst.org/neisseria/ were examined. Analysis of the porB encoding regions from the invasive meningococci has identified four new alleles and a potential association between porB alleles, serogroup, and clonal complexes. Through computer-based modeling and analysis of the electrostatic surface charges of PorB from these strains, loop charge segregation between PorB from invasive serogroups B and C was observed. Specifically, loops 1, 4, and 7 were negatively charged and L2 and L8 were mostly neutral in serogroup B isolates, while an overall homogeneous positive surface charge was present in PorB from invasive serogroup C strains. A higher PorB sequence variability was observed among carriage genomes, and a general prevalence of negative loop surface charges. The surface charge differences in PorB from serogroups B and C invasive and carriage strains may, in part, influence the outcomes of Neisseriae interactions with host cells. V C 2016 IUBMB Life, 68(6): [488][489][490][491][492][493][494][495] 2016

Heterogeneity in non‐epitope loop sequence and outer membrane protein complexes alters antibody binding to the major porin protein PorB in serogroup B Neisseria meningitidis

“…Indeed, heterogeneity in PorB loop sequences has been shown to affect loop surface charge. The BB1350 L5, for example, exhibits an overall neutral charge while that of MC58 is positive (Stefanelli et al ., ), suggesting the possibility that loop charge state may alter PorB interactions with PorA. This may account for the difference in the binding pattern of Z4 to Cu385 and Ch501 PorB when expressed in their own native membranes (containing PorA serosubtypes P1.19,15 and P1.5,10, respectively) versus that of MC58 (P1.7,16).…”

“…Yet, surveys of endemic and epidemic meningococcal strains have revealed a preservation of certain prevalent PorB sequence types that are commonly associated with invasive disease (Bash et al ., ; de Filippis et al ., ; Stefanelli et al . ), suggesting that pressure for an association of favored loop sequences occurs in nature. Mathematical modeling provides one explanation for this apparent paradox, that uniform immune responses directed against strongly immunogenic loop sequences permits survival of those strains expressing non‐overlapping antigenic types (Gupta et al ., ), favoring gene replacement with heterologous sequence over partial genetic exchange.…”

Neisseriae internalization by epithelial cells is enhanced by TLR2 stimulation

“…It has been established that criticalr esidues in the surface-exposed loop regions of PorB influence organisms’ internalization by host cells [9, 13, 17] and may be involved in the hyper-invasive features of some NM strains [18]. Our group has recently reported a prevalence of negative surface charges is reported in loops 1, 4, 6 and 7 of PorB from invasive meningococcal serogroup B clinical isolates, while overall positive charges are reported in the corresponding PorB loops of invasive meningococcal serogroup C clinical isolates [19]. The sequence variability of PorB also influences interactions with TLR2 and the subsequent intracellular signaling pathways [23, 24, 28].…”

“…NM and GC porins promote epithelial cell invasion [11-16] while NL PorB reduces it as shown in a GC mutant strain expressing NL PorB in place of GC PorB [17]. The sequence variability of PorB has been linked to the pathogenicity of hyper-invasive and invasive meningococcal strains [18, 19] and to some of its host cell-associated functions (serum resistance, host cell survival, immune stimulation [20]). Critical residues in the surface-exposed loops of PorB influence organisms’ invasion of epithelial cells and the direct interaction of PorB with host cell receptors associated with bacterial adhesion/invasion (i.e.…”

<em>Neisseria meningitidis</em> Serogroup B Lipopolysaccharides Induce a Lower Pro-Inflammatory Effect within the Proteoliposome Used in Cuban Anti-Meningococcal Vaccines

“…These receptors include Toll-like receptors (TLR), collectins, CD14, and mannose binding protein 16,32 . Among the members of the TLR family described, TLR4 is known as the receptor for some LPS and TLR2 for peptidoglycan and bacterial lipoproteins, particularly PorB of N. meningitides 30,15 .…”