Structure and evolution of the repetitive gene encoding streptococcal protein G

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Streptococcus species possess cell-wall-bound receptors involved in host interactions.
• Immunoglobulin G (IgG) binding proteins are important virulence factors in some bacteria.
• Understanding the genetic basis of these proteins can reveal insights into bacterial evolution and host evasion strategies.

Purpose of the Study:

• To determine the complete DNA sequence of the gene encoding the immunoglobulin G binding protein from Streptococcus G148.
• To analyze the genetic structure and identify potential regulatory elements and functional domains.
• To compare the gene with related sequences from other streptococcal strains to understand evolutionary relationships.

Main Methods:

• DNA sequencing of the structural gene and flanking regions.
• Bioinformatic analysis to identify open reading frames and predict protein features.
• N-terminal sequencing of the mature protein to confirm signal peptide cleavage.
• Comparative sequence analysis with homologous genes from other bacterial strains.

Main Results:

• The complete gene sequence and flanking regions were determined, revealing an open reading frame for a 63,294 Da preprotein.
• N-terminal sequencing confirmed a 33-amino acid signal peptide.
• Extensive internal homologies were observed, characteristic of cell-wall-bound receptors in gram-positive bacteria.
• Significant size variations were found in a related gene from another strain, attributed to differing numbers of internal repeats.

Conclusions:

• The gene structure of the Streptococcus G148 IgG binding protein exhibits internal homologies and suggests an evolutionary pathway involving multiple gene duplications.
• Variations in internal repeat numbers contribute to size heterogeneity among related streptococcal genes.
• The findings provide insights into the molecular evolution and structural diversity of bacterial cell-wall-bound receptors.