Patterns of structural and sequence variation within isotype lineages of the Neisseria meningitidis transferrin receptor system

Abstract

Neisseria meningitidis inhabits the human upper respiratory tract and is an important cause of sepsis and meningitis. A surface receptor comprised of transferrin-binding proteins A and B (TbpA and TbpB), is responsible for acquiring iron from host transferrin. Sequence and immunological diversity divides TbpBs into two distinct lineages; isotype I and isotype II. Two representative isotype I and II strains, B16B6 and M982, differ in their dependence on TbpB for in vitro growth on exogenous transferrin. The crystal structure of TbpB and a structural model for TbpA from the representative isotype I N. meningitidis strain B16B6 were obtained. The structures were integrated with a comprehensive analysis of the sequence diversity of these proteins to probe for potential functional differences. A distinct isotype I TbpA was identified that co-varied with TbpB and lacked sequence in the region for the loop 3 α-helix that is proposed to be involved in iron removal from transferrin. The tightly associated isotype I TbpBs had a distinct anchor peptide region, a distinct, smaller linker region between the lobes and lacked the large loops in the isotype II C-lobe. Sequences of the intact TbpB, the TbpB N-lobe, the TbpB C-lobe, and TbpA were subjected to phylogenetic analyses. The phylogenetic clustering of TbpA and the TbpB C-lobe were similar with two main branches comprising the isotype 1 and isotype 2 TbpBs, possibly suggesting an association between TbpA and the TbpB C-lobe. The intact TbpB and TbpB N-lobe had 4 main branches, one consisting of the isotype 1 TbpBs. One isotype 2 TbpB cluster appeared to consist of isotype 1 N-lobe sequences and isotype 2 C-lobe sequences, indicating the swapping of N-lobes and C-lobes. Our findings should inform future studies on the interaction between TbpB and TbpA and the process of iron acquisition.

Utility of Hybrid Transferrin Binding Protein Antigens for Protection Against Pathogenic Neisseria Species

“…Phylogenetic analysis of TbpA and TbpB sequences from N. meningitidis and N. gonorrhoeae have demonstrated that the gonococcal diversity exists predominantly as either one subset (TbpA) or two subsets (TbpB) of the isotype II-type meningococcal diversity (Figure 3). When compared at the same scale, TbpB contains substantially more variability than does TbpA within each isotype, however the isotype distinction appears in both TbpA and TbpB sequences, with strains appearing to be consistently isotype I or isotype II, as previously reported (40).…”

“…The sequences of the chosen TbpA loops were compared across a collection of three N. gonorrhoeae strains (Figure 4, bottom three sequences) and eight N. meningitidis strains (Figure 4, top eight sequences) selected to represent the overall diversity of Neisseria TbpAs (as seen in Figure 3). The overall sequence diversity of TbpA parallels the sequence diversity of the TbpB C-lobe, which divides the C-lobe variants into an isotype I cluster with a smaller size C-lobe (also reflected in the overall TbpB size) and a larger size isotype II C-lobe (40). Thus, the N. meningitidis collection included six strains expressing isotype II TbpBs and two strains expressing isotype I TbpBs (B16B6 and 90/18311) while all three N. gonorrhoeae strains expressed isotype II TbpBs.…”

Identification of a Large Family of Slam-Dependent Surface Lipoproteins in Gram-Negative Bacteria

“…Table below lists the accession numbers for all Slam-dependent SLP structures deposited to the Protein Data Bank (PDB). Primary references for TbpB (Moraes et al, 2009 ; Calmettes et al, 2011 , 2012 ; Noinaj et al, 2012 ; Adamiak et al, 2015 ; Frandoloso et al, 2015 ), LbpB N-lobe (Arutyunova et al, 2012 ; Brooks et al, 2014 ), HpuA (Wong et al, 2015 ), and fHbp (Cantini et al, 2009 ; Schneider et al, 2009 ; Cendron et al, 2011 ; Scarselli et al, 2011 ; Johnson et al, 2012 ; Konar et al, 2015 ) structures are also included.…”

Hybrid Antigens Expressing Surface Loops of ZnuD From Acinetobacter baumannii Is Capable of Inducing Protection Against Infection

“…The original "loopless C-lobe" (21) was derived from the N. meningitidis TbpB from strain M982 in which the larger loop regions not resolved in the crystal structure (loop 20 413−439 , loop 21 444−474 , loop 23 499−520 , loop 31 657−676 ) (34) were replaced with equivalent short linking regions identified in the structure of an Actinobacillus pleuropneumoniae TbpB (35). Two variants of the original LCL were prepared which involved the replacement of a segment of the handle domain (LCLv2) or loop 31 (LCLv3) were derived from the TbpB from N. meningitidis strain B16B6 (36) to generate a more cross-protective scaffold when used in experiments with N. meningitidis. The M982 LCL with the loop region derived from the B16B6 TbpB (loop 31 657−676 ), LCLv3, was used as the starting scaffold for hosting the loops from A. baumannii ZnuD and is localized to insertion site 4 (Figure 2).…”