Structure determination and analysis of a bacterial chymotrypsin from Cellulomonas bogoriensis.

The crystal structure of a secreted chymotrypsin from the alkaliphile Cellulomonas bogoriensis has been determined using data to 1.78 A resolution and refined to a crystallographic R factor of 0.167. The crystal structure reveals a large P1 substrate-specificity pocket, as expected for chymotrypsins. The structure is compared with close structural homologues. This comparison does not reveal clear reasons for the alkali tolerance of the enzyme, but the greater compactness of the structure and lowered hydrogen bonding may play a role.

The mammalian cell entry operon 1 (mce1) of mycobacterium leprae and mycobacterium tuberculosis.

The genome project on Mycobacterium tuberculosis H37Rv has revealed four mammalian cell entry (MTmce1-4) operons putatively involved with entry and survival of mycobacteria in host cells. A homologous operon to the MTmce1 operon was identified in cosmid B983 of Mycobacterium leprae. By comparison with M. tuberculosis, several mutations, or sequencing errors, were predicted at specific sites causing frame shifts in the MLyrbE1A, MLyrbE1B and MLmce1D genes. Using targeted sequencing, sequence errors were identified. The corrected MLmce1 operon sequence appears to be highly homologous to the MTmce1 operon, and similarly encodes eight potential genes. Thus, both M. tuberculosis and M. leprae mce1 operons may be functional and involved in host cell targeting.

Diversity of capsular polysaccharide synthesis gene clusters in Streptococcus pneumoniae.

Streptococcus pneumoniae comprises 90 serotypes, each one having its own specific polysaccharide capsule. In order to explore the diversity of capsular polysaccharide synthesis (cps) gene clusters in S. pneumoniae, we performed cross-hybridizations between the 12 cps genes of S. pneumoniae serotype 14 and chromosomal DNA of 26 strains comprising 26 different capsule types. Large variations in the hybridization patterns were observed. The genes cps14A to cps14D are conserved in most serotypes. Sequences homologous to cps14I to cps14L were only observed in the four types of serogroup 15, which all have a capsule structure similar to that of type 14. By using a cps14E knock-out construct, cpsE mutants of the pneumococcal types 9N, 13, and 15B were obtained. These mutants were unencapsulated and showed reduced glycosyltransferase activity, indicating that the pneumococcal types 9N, 13, and 15B express a glucosyl-1-phosphate transferase which is homologous to Cps14E. Glycosyltransferase assays showed that among 21 pneumococcal types which contain glucose in the core of their capsule polysaccharide, 19 types express glucosyl-1-phosphate transferase activity. However, not all of these types hybridized strongly with Cps14E, the type 14 glucosyl-1-phosphate transferase gene. Thus, pneumococci possess glucosyltransferase genes distinct from cps14E, but encoding enzymes with identical activity. All serotypes which synthesized lipid-linked lactose intermediates in glycosyltransferase activity assays (type 11B, 13, 15F, 15A, 15B, 15C) hybridized with cps14G. This gene encodes a galactosyltransferase which catalyzes the addition of 1,4-linked beta-galactose to lipid-linked glucose. The cps14G homologues in type 11B, 13, 15F, 15A, 15B, and 15C may encode a similar beta-galactosyltransferase activity as cps14G in type 14.

Functional analysis of glycosyltransferases encoded by the capsular polysaccharide biosynthesis locus of Streptococcus pneumoniae serotype 14.

Bacteria belonging to the species Streptococcus pneumoniae vary in their capsule. Presently, 90 capsular serotypes are known, all possessing their own specific polysaccharide structure. Little is known about the biosynthesis of these capsular polysaccharides. The cps locus of S. pneumoniae serotype 14 was cloned. So far, 7 open reading frames have been sequenced, cps14B to cps14H. The gene products are similar to proteins involved in bacterial polysaccharide biosynthesis, both of Gram-negative and -positive micro-organisms. Gene-specific mutants were created for cps14D to cps14H by insertional mutagenesis. All mutants no longer agglutinated with a monoclonal antibody against type 14 capsule polysaccharides. The biosynthetic function of cps14E and cps14G was determined by analysis of the intermediates in the synthesis of the oligosaccharide subunit, formed in membrane preparations of the wild-type and mutant strains and in membrane preparations of Escherichia coli expressing the pneumococcal glycosyltransferases. The enzyme encoded by cps14E is a glucosyl-1-phosphate transferase that links glucose to a lipid carrier, the first step in the biosynthesis of the type 14 repeating unit. The gene product of cps14G encodes a beta-1,4-galactosyltransferase, the enzyme responsible for the second step in the subunit synthesis, the transfer of galactose to lipid-linked glucose.

Capsular polysaccharide synthesis in Streptococcus pneumoniae serotype 14: molecular analysis of the complete cps locus and identification of genes encoding glycosyltransferases required for the biosynthesis of the tetrasaccharide subunit.

We have reported previously on seven genes (cps14B-H) of Streptococcus pneumoniae serotype 14, which are part of the type 14 capsular polysaccharide synthesis (cps14) locus. This study describes the cloning and sequencing of the remaining part of the cps14 locus. The entire cps14 gene cluster consists of 12 open reading genes (cps14A to cps14L), which appear to be arranged as a single transcriptional unit. The flanking regions of the cps14 locus contain vestiges of insertion elements. Moreover, a 115-bp-long repeated DNA element, which is also present in several other intergenic regions on the pneumococcal chromosome, has been identified upstream of cps14A. All 12 open reading frames (ORFs) were inactivated by the insertion of a tetracycline resistance cassette. The cps14A to cps14J and cps14L mutants were unencapsulated, whereas only a limited amount of capsular polysaccharide was expressed by a cps14K insertion mutant. Comparison with DNA and protein sequences available in databases allowed us to predict functions for four out of the five new cps14 gene products. The biosynthetic function of Cps14I was determined experimentally by analysis of intermediates in the synthesis of the type 14 tetrasaccharide subunit, catalysed by membrane preparations of Escherichia coli expressing pneumococcal glycosyltransferases. The cps14I gene encodes the beta-1,3-N-acetylglucosaminyltransferase activity necessary for the addition of the third sugar in the synthesis of the type 14 repeating unit. The activity encoded by cps14J was established using a synthetic glycosyltransferase acceptor: cps14J encodes a beta-1,4-galactosyltransferase, which requires beta-linked GlcNAc as an acceptor. Thus, Cps14J is responsible for the addition of the last (fourth) sugar in the synthesis of the type 14 subunit.

The capsule polysaccharide synthesis locus of streptococcus pneumoniae serotype 14: Identification of the glycosyl transferase gene cps14E.

To identify a chromosomal region of Streptococcus pneumoniae serotype 14 involved in capsule polysaccharide synthesis, two strategies were used: (i) Tn916 mutagenesis, followed by the characterization of four unencapsulated mutants, and (ii) cross-hybridization with a capsule polysaccharide synthesis gene (cps) probe from S. agalactiae, which has a structurally similar capsule. The two approaches detected the same chromosomal region consisting of two adjacent EcoRI fragments. One of these EcoRI fragments was cloned and hybridized with a cosmid library. This resulted in clone cMKO2. A similar cosmid clone was obtained from an unencapsulated Tn916 mutant, Spnl4.H. Sequence analysis of the two cosmid clones revealed that in the Tn916 mutant, a gene, cps14E, which is homologous to other bacterial genes encoding glycosyl transferases, had been inactivated. An open reading frame immediately downstream of cps14E, designated cps14F, shows no significant homology with any known genes or proteins. A functional assay showed that cps14E encodes a glycosyl transferase and that a gene-specific knockout mutant lacks this enzyme activity, whereas inactivation of cps14F does not have this effect.