“The polysaccharide capsule of Streptococcus pneumoniae is

“The polysaccharide capsule of Streptococcus pneumoniae is the main virulence find more factor making the bacterium resistant to phagocytosis. The galU gene of S. pneumoniae encodes a UDP-glucose pyrophosphorylase absolutely required

for capsule biosynthesis. In silico analyses indicated that the galU gene is co-transcribed with the gpdA gene, and four putative promoter regions located upstream of gpdA were predicted. One of them behaved as a functional promoter in a promoter reporter system. It is conceivable that the sequence responsible for initiating transcription of gpdA-galU operon is an extended −10 site TATGATA(T/G)AAT. Semi-quantitative real-time reverse transcription PCR experiments indicated that galU was expressed mainly in the exponential phase of growth. Streptococcus pneumoniae is a leading human pathogen causing both mucosal (such as otitis media and pneumonia) and systemic diseases (including septicemia and meningitis). To date, 93 different pneumococcal Y27632 capsular types have been described (Henrichsen, 1995; Park et al.,

2007; Bratcher et al., 2010; Calix & Nahm, 2010). This remarkable phenotypic variability appears to be present also at the genetic level (Bentley et al., 2006). Early studies showed that uridine diphosphoglucose (UDP-Glc) is a key component in the GPX6 biosynthetic pathway of pneumococcal capsular polysaccharides containing glucose, galactose, and/or UDP-glucuronic or UDP-galacturonic acids (Mills & Smith, 1965).

At least one of these sugars is a component of every capsular polysaccharide of S. pneumoniae (Kamerling, 2000). The enzyme UTP-Glc-1-phosphate uridylyltransferase (UDP-Glc pyrophosphorylase; EC is encoded by the galU gene. This enzyme catalyzes the formation of UDP-Glc, which is the substrate for the synthesis of UDP-glucuronic acid. Also, UDP-Glc is also required for the interconversion of galactose and glucose by way of the Leloir pathway (Frey, 1996). Previously, the galU gene was cloned and overexpressed, and the gene product was biochemically characterized (Mollerach et al., 1998; Bonofiglio et al., 2005). In addition, knockout galU mutants of type 1 and type 3 pneumococci are unable to synthesize a detectable capsular polysaccharide. Southern blot hybridization experiments using DNAs prepared from pneumococcal isolates belonging to different types showed that every strain tested contained a galU homologue (Mollerach et al., 1998). Thus, the UDP-Glc pyrophosphorylase, which is directly involved in the synthesis of the capsular polysaccharide in S. pneumoniae, might represent a suitable target in the search for inhibitors to control the biosynthesis of the main pneumococcal virulence factor.

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