A neuraminidase from Streptococcus pneumoniae has the features of a surface protein

Abstract

A gene from Streptococcus pneumoniae (nanA), with features entirely consistent with a neuraminidase gene, has been sequenced. High levels of neuraminidase activity were obtained after cloning of this gene, without flanking sequences, into a high-expression vector. RNA hybridization studies have shown that the gene is transcribed by a virulent pneumococcus strain. The predicted molecular weight of the protein and certain amino acid sequences are typical of other neuraminidases. NanA contains the four copies of the sequence SXDXGXTW that is present in all the bacterial neuraminidases previously described. Kyte and Doolittle analysis showed that NanA is a hydrophilic protein with hydrophobic domains at the N terminus and the C terminus. A putative signal peptide was found in the N terminus of this protein, indicating that the protein is exported from the pneumococcus. The C terminus has the features of the anchor motif found in other surface proteins from gram-positive bacteria. Electron microscopy studies showed the presence of neuraminidase associated with the cell surface of the pneumococcus. Streptococcus pneumoniae is one of the major causes of lower respiratory tract infections, septicemia, and meningitis in humans (3). It produces several factors with properties that suggest that they could play a role in the virulence of this organism (6). One of these factors is a neuraminidase, an enzyme responsible for the cleavage of N-acetylneuraminic acid (NANA) from mucin, glycoproteins, and gangliosides (17, 37). Although the precise role of the neuraminidase in pathogenesis has not been established, neuraminidase treatment of mucus could decrease its viscosity, thereby enhancing the colonization of the underlying tissues by the pneumococcus (37). Furthermore, removal of NANA by the neuraminidase could expose surface receptors for the pneumococcus (1). There are some experimental data supporting the idea of a role in virulence for pneumococcal neuraminidase. All clinical isolates of the pneumococcus tested were positive for the production of this enzyme (19, 26). In patients with pneumococcal infection there was a direct relationship between the level of NANA in cerebrospinal fluid and the development of coma and an adverse outcome (26). Intracerebral inoculation of mice with purified neuraminidase caused neurological signs and death (18). Mice immunized with purified neuraminidase were partially protected against pneumococcal infection (21). However, intrathecal inoculation of the enzyme in dogs did not produce any symptoms (27). Biochemical studies of pneumococcal neuraminidase have revealed a range of molecular weights and have led to controversy over the number and size of the neuraminidase(s) produced by the pneumococcus (22, 37, 40-42). Molecular

Streptococcus pneumoniae: virulence factors and variation

“…Neuraminidase cleaves N-acetylneuraminic acid from glycolipids, lipoproteins and oligosaccharides on cell surfaces and in body fluids [39]. This may cause direct damage to the host or it may unmask potential binding sites for the organism.…”

Pneumococcal modification of host sugars: a major contributor to colonization of the human airway?

“…The majority of pneumococcal glycosidases have distinct cleavage specificities (Table 1), the exception being the expression of up to three neuraminidases that cleave terminal sialic acid (NanA, NanB, and NanC) (Camara et al, 1994;Berry et al, 1996;Tettelin et al, 2001). It has been demonstrated that NanA and NanB possess neuraminidase activity; however, the enzymatic activity of NanC remains to be confirmed.…”

The mmsA locus of Streptococcus pneumoniae encodes a RecG‐like protein involved in DNA repair and in three‐strand recombination

“…These enzymes are responsible for the conversion of L-alanine into D-alanine which is used in the construction of the peptidoglycan # 1996 Blackwell Science Ltd, Molecular Microbiology, 19, 1035-1045 shown as open boxes. Genes identified in the region, including the previously described nanA gene (Cámara et al, 1994), and the BOX element (Martin et al, 1992a), are indicated by shaded arrows, except for the putative 5' (unsequenced) extremity of the alaR homologue. The tentative location of the mmsA1 mutation is indicated by a vertical arrow.…”