Structure and evolution of the repetitive gene encoding streptococcal protein G

Abstract

The complete sequence of the structural gene encoding the immunoglobulin G binding protein from Streptococcus G148 has been determined, as well as its 5' and 3' flanking sequences. The sequence reveals an open reading frame encoding a putative preprotein with a relative molecular mass of 63294. N-Terminal sequencing of the mature protein, spontaneously released from streptococcal cells, demonstrates that the signal peptide consists of 33 amino acids. The DNA sequence reveals extensive internal homologies similar to other cell-wall-bound receptors from gram-positive bacteria. Comparisons with a related gene previously isolated from another strain of streptococci revealed large differences in size, due to variations in the number of internal repeats. The structure of the gene suggests an evolution through multiple duplications.Several gram-positive bacteria contain cell-surface proteins, probably involved in the pathogenicity of these bacteria in animals and man [l]. The best known receptor is the protein A from Staphylococcus aureus, which has found extensive use in quantitative and qualitative immunological techniques due to its binding to the Fc fragment of immunoglobulins [2]. Other receptors include the M protein from Streptococcus pyogenes [3], which is a virulence factor enabling the streptococci to resist clearance by phagocytic cells, and the fibronectin receptor from S. aureus which binds to fibronectin [4]. In addition, a number of immunoglobulin Fc receptors with differential binding to various IgG subclasses have been isolated from Streptococcus group A, C and G [5 -81.Recently, the genes encoding staphylococcal protein A [9] and streptococcal M protein [3] were cloned and sequenced. This revealed in both cases repetitive structures, suggesting an evolution of these genes through multiple duplications of internal fragments of different sizes. Both genes encode proteins consisting of a signal peptide followed by a repetitive receptor region, a proline-rich region and a hydrophobic C-terminus. Thus, although only low homology could be detected at the deduced primary sequence level, the overall structure of both genes suggests a common mechanism by which these receptors associate to the cell surface.We have earlier reported on the cloning of the IgG receptor from Streptococcus G148, called protein G, and the characterization of the part responsible for IgG binding [lo]. Here, we describe the cloning and sequencing of its 5'-end of the protein G gene from strain G148, as well as that of the 5' and 3' flanking regions. This has enabled structural comparisons to the related protein G gene from strain GX7809 [ll], showing large differences in size and number of internal repeats, despite high sequence homology. The results suggest a model for the evolution of this cell-wall-bound repector .

Nucleotide sequence of the gene for a fibronectin-binding protein from Staphylococcus aureus: use of this peptide sequence in the synthesis of biologically active peptides.

“…Fibronectin has also been shown to increase adherence of bacteria to neutrophils (36, 37), although whether bacterial uptake by neutrophils is facilitated by fibronectin remains unclear (36)(37)(38)(39). However, regardless of opsonic activity, binding of plasma fibronectin to the bacterial surface might block adhesion receptors on S. aureus, thus representing an important defense mechanism against tissue invasion (35,(40)(41)(42) (44,46,47). The FnBP signal peptide is apparently recognized by the E. coli membranes (17).…”

The serum albumin‐binding domain of streptococcal protein G is a three‐helical bundle: a heteronuclear NMR study

“…Depending on the Streptococcus strain, SPG contains two or three immunoglobulin-binding domains of approximate 55 residues, denoted B1 through B3 or C1 through C3 by different authors [11][12][13] (Fig. la).…”

Complement assembly of two fragments of the streptococcal protein G B1 domain in aqueous solution

“…Protein G is a immunoglobulin G binding protein located on the cell wall of group G streptococci containing the immunoglobulin G binding domains, B l, B2 and B3 that are nearly identical [18][19][20]. Although these domains comprise only 56 amino acid residues without disulfide bridges, they have high heat denaturation points.…”