Molecular studies on IgA1 protease and neuraminidase from Streptococcus pneumoniae.

Streptococcus pneumoniae is an important human pathogen responsible for lower respiratory tract infections, septicemia and meningitis. It produces IgAl protease and neuraminidase which may be of relevance in the pathogenesis of pneumococcal disease. A LambdaEMBL301 genomic library from S. pneumoniae strain R36A was made. A stable clone expressing IgAl protease activity was isolated from this library. Preliminary hybridization studies suggested the pneumococcal authenticity of this IgAl protease recombinant. From the same pneumococcal genomic library a gene expressing neuraminidase activity was also isolated. Restriction mapping and DNA hybridization studies revealed that this gene is distinct from another pneumococcal neuraminidase gene previously cloned. Both genes were found simultaneously present in several different pneumococcal serotypes. The DNA sequence of the pneumococcal neuraminidase gene plus flanking regions was determined. The predicted amino acid sequence of this neuraminidase corresponds to a mainly hydrophilic protein. This neuraminidase presents a putative signal peptide near the N-terminus. It also contains a typical surface anchor motif in the C-terminus which is common to other surface proteins from Gram-positive organisms. N-terminal to this motif there is a region containing twenty amino acids tandemly repeated three times. Regions of homology between this protein and other neuraminidases were found. Electron microscopy studies using immunogold staining showed the presence of pneumococcal neuraminidase associated to the surface of the pneumococcus. Analysis of the neuraminidase DNA flanking regions revealed the presence of DNA repetitive elements (BOXES). Databases analysis showed the presence of some of these elements in the vicinity of pneumococcal genes related with virulence and competence.