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Expression of factor H binding protein in meningococcal strains can vary at least 15-fold and is genetically
Massimiliano Biagini1, Marco Spinsanti1, Gabriella De Angelis1
1GSK Vaccines, 53100 Siena, Italy.
Abstract:
Factor H binding protein (fHbp) is a lipoprotein of Neisseria meningitidis important for the survival of the bacterium in human blood and a component of two recently licensed vaccines against serogroup B meningococcus (MenB). Based on 866 different amino acid sequences this protein is divided into three variants or two families. Quantification of the protein is done by immunoassays such as ELISA or FACS that are susceptible to the sequence variation and expression level of the protein. Here, selected reaction monitoring mass spectrometry was used for the absolute quantification of fHbp in a large panel of strains representative of the population diversity of MenB. The analysis revealed that the level of fHbp expression can vary at least 15-fold and that variant 1 strains express significantly more protein than variant 2 or variant 3 strains. The susceptibility to complement-mediated killing correlated with the amount of protein expressed by the different meningococcal strains and this could be predicted from the nucleotide sequence of the promoter region. Finally, the absolute quantification allowed the calculation of the number of fHbp molecules per cell and to propose a mechanistic model of the engagement of C1q, the recognition component of the complement cascade.
Insights
Factor H binding protein (fHbp) levels vary significantly in Neisseria meningitidis strains, impacting bacterial survival. This study quantifies fHbp expression, revealing variant-specific differences and their link to complement resistance.
Area of Science:
- Microbiology
- Immunology
- Proteomics
Background:
- Factor H binding protein (fHbp) is crucial for Neisseria meningitidis survival and a key component in vaccines against serogroup B meningococcus (MenB).
- Existing quantification methods like ELISA and FACS are limited by protein sequence variation and expression levels.
- fHbp exhibits sequence variation, categorized into three variants across two families.
Purpose of the Study:
- To accurately quantify fHbp absolute levels across diverse MenB strains using mass spectrometry.
- To investigate the correlation between fHbp expression levels, its variants, and susceptibility to complement-mediated killing.
- To model the interaction of fHbp with the complement cascade component C1q.
Main Methods:
- Selected reaction monitoring mass spectrometry (SRM-MS) for absolute quantification of fHbp.
- Analysis of a large panel of MenB strains representing population diversity.
- Correlation analysis between fHbp expression, variant type, promoter sequence, and complement susceptibility.
Main Results:
- fHbp expression levels varied by at least 15-fold among MenB strains.
- Variant 1 strains showed significantly higher fHbp expression compared to variant 2 and 3 strains.
- Complement-mediated killing susceptibility correlated with fHbp expression, predictable from promoter nucleotide sequences.
Conclusions:
- Absolute quantification of fHbp provides a more reliable measure than immunoassays.
- fHbp expression levels and variants significantly influence MenB's resistance to complement.
- The study provides insights into fHbp's role in complement evasion and potential vaccine efficacy.
