Neisseria adhesin A variation and revised nomenclature scheme.

Neisseria Adhesin A Variation and Revised Nomenclature Scheme Stefania Bambini,a Matteo De Chiara,a Alessandro Muzzi,a Marirosa Mora,a Jay Lucidarme,b Carina Brehony,c Ray Borrow,b Vega Masignani,a Maurizio Comanducci,a* Martin C. J. Maiden,c Rino Rappuoli,a Mariagrazia Pizza,a Keith A. Jolleyc Novartis Vaccines and Diagnostics, Siena, Italya; Public Health England, Manchester, United Kingdomb; Department of Zoology, University of Oxford, Oxford, United Kingdomc Neisseria adhesin A (NadA), involved in the adhesion and invasion of Neisseria meningitidis into host tissues, is one of the major components of Bexsero, a novel multicomponent vaccine licensed for protection against meningococcal serogroup B in Europe, Australia, and Canada. NadA has been identified in approximately 30% of clinical isolates and in a much lower proportion of carrier isolates. Three protein variants were originally identified in invasive meningococci and named NadA-1, NadA-2, and NadA-3, whereas most carrier isolates either lacked the gene or harbored a different variant, NadA-4. Further analysis of isolates belonging to the sequence type 213 (ST-213) clonal complex identified NadA-5, which was structurally similar to NadA-4, but more distantly related to NadA-1, -2, and -3. At the time of this writing, more than 89 distinct nadA allele sequences and 43 distinct peptides have been described. Here, we present a revised nomenclature system, taking into account the complete data set, which is compatible with previous classification schemes and is expandable. The main features of this new scheme include (i) the grouping of the previously named NadA-2 and NadA-3 variants into a single NadA-2/3 variant, (ii) the grouping of the previously assigned NadA-4 and NadA-5 variants into a single NadA-4/5 variant, (iii) the introduction of an additional variant (NadA-6), and (iv) the classification of the variants into two main groups, named groups I and II. To facilitate querying of the sequences and submission of new allele sequences, the nucleotide and amino acid sequences are available at http://pubmlst.org/neisseria/NadA/. N eisseria adhesin A (NadA) is a trimeric autotransporter protein, with a role in adhesion to and invasion of host tissues, which is present in a subset of meningococcal strains (1). Recent studies have shown that NadA is involved in interaction with and stimulation of immune cells during infection (2–4) and in binding to the human chaperone Hsp90 (5, 6). Its predicted molecular structure is very similar to the known virulence-associated factors Yersinia adhesin A (YadA) and UspA2 (7, 8), which suggests that NadA is a member of the OCA (oligomeric coiled-coil adhesin) family (9). NadA forms oligomers which are anchored via a transmembrane domain into the outer membrane and has been shown to be immunogenic in animal models (10). Further, children recovering from invasive meningococcal disease produce specific antibody responses against this antigen (11). NadA expression is regulated at the transcriptional level by the length variation of a tandem repeat region located in the gene promoter (12, 13), with expression regulated by NadR, a repressor molecule (14–16). Expression can be induced by the use of 4-hydroxyphenyl acetic acid, a small molecule secreted in human saliva, which inhibits NadRdependent repression (14). Recent data indicate protein upregulation in vivo (15). In addition, MtrR, a transcriptional regulator, has a negative regulatory impact on NadA expression, especially when overexpressed (17). Nucleotide sequence analyses of nadA have shown that the gene is present in approximately 30% of clinical isolates but in a much lower proportion (16%) of isolates obtained from asymptomatic carriage (10, 18–20). The nadA gene is present in almost all isolates belonging to the hyperinvasive sequence type 8 (ST-8), ST-11, ST-32, and ST-213 clonal complexes (cc) tested to date but is rarely present in ST-41/44 and ST-269 cc isolates. Three variants, named NadA-1, NadA-2, and NadA-3, were originally identified in pathogenic strains (10). nadA was initially grouped into three alleles based on the different sizes of the PCR patterns obtained with primers external to the nadA gene insertion site. Once discovered, the NadA-1, -2, and -3 proteins were inappropriately 966 cvi.asm.org Clinical and Vaccine Immunology referred to as alleles because of the low diversity of the encoding genes, sharing 84 to 99% identity. In particular, NadA-2 and NadA-3 were very similar (the corresponding genes shared ⱖ97% identity). Each NadA variant was associated with meningococcal clonal complexes (21). In particular, NadA-1 was associated with 100% of ST-32 cc isolates tested. NadA-2 and NadA-3 were found in ST-8 and ST-11 ccs and in a few other meningococcal lineages (some ST-18 cc strains and some unassigned clonal complexes). NadA-3 was also present in ST-174 cc strains, mostly serogroup Y (22). NadA-1, -2, and -3 were shown to form high-molecularweight oligomers on the meningococcal surface, to mediate adhesion and invasion into epithelial cells in vitro, to induce high titers of cross-reactive bactericidal antibodies, and to induce protection in the infant rat model (10). The NadA-4 variant was originally described in meningococci isolated from healthy people (19). NadA-4 consists of 323 amino acids and is shorter than the NadA-1, NadA-2, and NadA-3 variants, which are composed of 362, 398, and 405 amino acids, respectively. Although shorter in length, the overall secondary structure and domain organizations are conserved. NadA-4 is exposed on the bacterial surface, where it forms high-molecular-weight Received 31 December 2013 Returned for modification 30 January 2014 Accepted 2 May 2014 Published ahead of print 7 May 2014 Editor: D. L. Burns Address correspondence to Rino Rappuoli, . * Present address: Maurizio Comanducci, Crucell, Leiden, The Netherlands. S.B. and M.D.C. contributed equally to this work. Supplemental material for this article may be found at http://dx.doi.org/10.1128 /CVI.00825-13. Copyright © 2014, American Society for Microbiology. All Rights Reserved. doi:10.1128/CVI.00825-13 p. 966 –971 July 2014 Volume 21 Number 7 Neisseria Adhesin A Nomenclature Scheme FIG 1 (A) SplitsTree representation showing the nadA gene variation. The genes encoding the different protein variants are circled and shown in different colors. The two main groups are indicated by traced circles. Two hybrid forms are also reported. (B) Neighbor-joining tree showing the distribution of different alleles corresponding to the six NadA protein variants. oligomers and binds to epithelial cells. Antibodies against the recombinant NadA-4 protein are bactericidal against homologous strains, whereas the activity against strains carrying the three other NadA variants is weak (19), suggesting that sequence variability is responsible for the absence of cross-reactivity with NadA-1, -2, and -3. Further analysis (...truncated)