Same, Same, but Different: Molecular Analyses of Streptococcus pneumoniae Immune Evasion Proteins Identifies new Domains and Reveals Structural Differences between PspC and Hic Variants

Abstract

PspC and Hic proteins of Streptococcus pneumoniae are some of the most variable microbial immune evasion proteins identified to date. Due to structural similarities and conserved binding profiles it was assumed over a long time that these pneumococcal surface proteins represent a protein family, comprising eleven subgroups. Recently, however, by evaluating more proteins larger diversity of individual proteins became apparent. In contrast to previous assumptions a pattern evaluation of six PspC and five Hic variants, each representing one of the previously defined subgroups, revealed distinct structural and likely functionally regions of the proteins, and identified nine new domains and new domain alternates. Several domains are unique to PspC and Hic variants, while other domains are shared with other S. pneumoniae and bacterial virulent determinants. This understanding improved pattern evaluation on the level of full-length proteins, allowed a sequence comparison on the domain level and furthermore identified domains with a modular composition. This novel concept allows a better characterization of variability, and modular domain composition of individual proteins, enables a structural and functional characterization at the domain level and furthermore shows substantial structural differences between PspC and Hic proteins. Such knowledge will also be useful for molecular strain typing, characterizing PspC and Hic proteins from new clinical S. pneumoniae strains, including those derived from patients who present with pneumococcal hemolytic uremic syndrome. Furthermore this analysis explains the role of multifaceted intact PspC and Hic proteins in pathogen host interactions. and can provide a basis for rational vaccine design. Author SummaryThe human pathobiont Streptococcus pneumoniae expresses highly polymorphic PspC or Hic proteins, which bind a repertoire of host immune regulators and combine antigenic variation with conserved immune evasion features. Understanding domain composition of each protein encoded by more than 60 000 pspC or hic genes deposited in the data banks defines their diversity, a role in immune escape and can furthermore delineate structure function approach for single protein domains. PspC and Hic proteins show variable domain composition and sequence diversity, which explain differences in binding of human regulators and likely in immune escape. The results of our analyses provide insights in the domain composition of these diverse immune evasion proteins, identifies new domains, defines domains which are unique to PspC or Hic variants, and identifies domains which are shared with other bacterial immune evasion proteins. These data have implication on cell wall attachment, surface distribution and in immune escape.