Disease relevance of dTDP-alpha-L-rhamnose

• Characterization of dTDP-4-dehydrorhamnose 3,5-epimerase and dTDP-4-dehydrorhamnose reductase, required for dTDP-L-rhamnose biosynthesis in Salmonella enterica serovar Typhimurium LT2 [1].
• Characterization of the dTDP-rhamnose biosynthetic genes encoded in the rfb locus of Shigella flexneri [2].
• Downstream of cap1K, one truncated and three complete open reading frames homologous to those involved in the biosynthesis of dTDP-rhamnose, a monosaccharide that does not participate in the formation of type 1 polysaccharide, have been identified in all the clinical strains of type 1 pneumococcus tested [3].
• Genetic organization and sequence of the rfb gene cluster of Yersinia enterocolitica serotype O:3: similarities to the dTDP-L-rhamnose biosynthesis pathway of Salmonella and to the bacterial polysaccharide transport systems [4].
• The rml genes are involved in dTDP-rhamnose synthesis in Streptococcus mutans [5].

High impact information on dTDP-alpha-L-rhamnose

• The first two steps of the reaction are catalyzed by enzymes that are part of the well studied dTDP-l-rhamnose biosynthetic pathway, namely d-glucose-1-phosphate thymidyltransferase (RmlA) and dTDP-d-glucose-4,6-dehydratase (RmlB) [6].
• The amino acid sequence of the dTDP-6-deoxy-L-lyxo-4-hexulose reductase forming dTDP-6-deoxy-L-talose shared only weak homology with that forming dTDP-L-rhamnose, despite the fact that these two enzymes catalyze the reduction of the same substrate and the products are determined by the stereospecificity of the reductase activity [7].
• Rhamnosyltransferase 1 (RhlAB) catalyses the synthesis of mono-rhamnolipid from dTDP-L-rhamnose and beta-hydroxydecanoyl-beta-hydroxydecanoate, whereas di-rhamnolipid is produced from mono-rhamnolipid and dTDP-L-rhamnose [8].
• Interestingly, the last four genes of the locus (cps19fL-O) exhibit very strong homology (up to 70% amino acid identity) to a portion of the Shigella flexneri rfb gene cluster encoding biosynthesis of dTDP-rhamnose [9].
• We have re-addressed the assignment of each gene of the dTDP-rhamnose pathway with the known enzymes of the pathway, in particular rfbC and rfbD [2].

Chemical compound and disease context of dTDP-alpha-L-rhamnose

• In previous studies the authors cloned and characterized the DNA sequence of the regions at both ends of the O7-specific lipopolysaccharide (LPS) biosynthesis cluster of Escherichia coli VW187 (O7:K1), and identified the biosynthetic genes for dTDP-rhamnose and GDP-mannose, as well as one of the candidate glycosyltransferases [10].
• We here report on the purification and characterization of glucose-1-phosphate thymidylyl-transferase, the first of four enzymes committed to biosynthesis of dTDP-L-rhamnose from Salmonella enterica strain LT2 [11].
• The results from the study of the biosynthetic dTDP-L-rhamnose pathway are discussed. dTDP-L-rhamnose is a key intermediate in many pathogenic bacteria, as it is the donor for L-rhamnose, which is found in the cell wall of important human pathogens, such as Mycobacteria tuberculosis and Salmonella typhimurium [12].
• The structure of RmlD from Salmonella enterica serovar Typhimurium has been determined, and complexes with NADH, NADPH, and dTDP-L-rhamnose are reported [13].

Biological context of dTDP-alpha-L-rhamnose

• A reporter plasmid to detect genes encoding enzymes of the dTDP-rhamnose pathway is described [2].
• The nucleotide sequence of the proximal half of the rfb region of Shigella flexneri has been determined, and the genes encoding enzymes involved in the biosynthesis of dTDP-rhamnose have been identified [2].
• The same phenotype was seen in a mutant obtained by allelic exchange in rmlD, another ORF in this dTDP-rhamnose biosynthetic cluster [14].
• Comparison of the four dTDP-L-rhamnose pathway genes (rml genes) of CPS types 1, 2, 6B, 18C, 19F, 19A, and 23F shows that they have the same gene order and are highly conserved [15].
• The S88 locus contained a four-gene operon for the biosynthesis of dTDP-L-rhamnose, an essential precursor for the sphingans [16].

Anatomical context of dTDP-alpha-L-rhamnose

• The Mycobacterium tuberculosis rmlC gene encodes dTDP-4-keto-6-deoxyglucose epimerase, the third enzyme in the M. tuberculosis dTDP-L-rhamnose pathway which is essential for mycobacterial cell-wall synthesis [17].

Associations of dTDP-alpha-L-rhamnose with other chemical compounds

• Knockout of an azorhizobial dTDP-L-rhamnose synthase affects lipopolysaccharide and extracellular polysaccharide production and disables symbiosis with Sesbania rostrata [18].
• The cluster encodes dTDP-L-rhamnose biosynthesis (rml operon), required for building up the polyrhamnan S-layer glycan, as well as for assembly and export of the elongated glycan chain, and its transfer to the S-layer protein [19].
• Glucose-1-phosphate thymidylyltransferase (RmlA; E.C. 2.7.7.24) is the first of four enzymes involved in the biosynthesis of dTDP-L-rhamnose, the precursor of L-rhamnose, a key component of the cell wall of many pathogenic bacteria [20].
• Heterologous expression of a partial elloramycin biosynthetic gene cluster indicated that the rate of dTDP-l-rhamnose synthesis, rather than the rate of glycosyl transfer, was limiting for glycoside formation in this strain [21].
• Introduction of plasmid pRHAM which contains four genes from the oleandomycin biosynthetic gene cluster, directing the synthesis of dTDP-rhamnose, led to a 26-fold increase of the production of glycosylated aminocoumarins [21].

Gene context of dTDP-alpha-L-rhamnose

• In addition, genes rfbA, -B, -C, and -D were identified in the genome of A. ferrooxidans, suggesting that it can also synthesize the EPS precursor dTDP-rhamnose [22].
• We conclude that the absence of a homolog for rfbC precludes the existence of a functional dTDP-rhamnose biosynthesis pathway in the gonococcal strains examined and that these genes are only maintained in N. gonorrhoeae either because of the presence of the galE gene or because of another as yet unrecognized function [23].
• Eight genes were identified in the rfb fragment: the rfbB-CAD cluster which encodes dTDP-rhamnose synthesis, rfbX which encodes a hydrophobic protein involved in assembly of the O antigen, rfc which encodes the O antigen polymerase, and two sugar transferase genes [24].
• A nonpolar mutation was made in the oac2 gene of Azorhizobium caulinodans. oac2 is an ortholog of the Salmonella typhimurium rfbD gene that encodes a dTDP-L-rhamnose synthase [18].
• We had isolated three genes (rmlA, rmlB, and rmlC) involved in dTDP-rhamnose synthesis in Streptococcus mutans and found that three genes were insufficient for dTDP-rhamnose synthesis (Y. Tsukioka, Y. Yamashita, T. Oho, Y. Nakano, and T. Koga, J. Bacteriol. 179:1126-1134, 1997) [25].

Analytical, diagnostic and therapeutic context of dTDP-alpha-L-rhamnose

• Genetic and sequence analyses of one such transport-defective mutant revealed that the transposon insertion occurred in an open reading frame (ORF) with homology to rmlC, a dTDP-rhamnose biosynthetic gene [14].
• Overexpression, purification, crystallization and preliminary structural study of dTDP-6-deoxy-L-lyxo-4-hexulose reductase (RmlD), the fourth enzyme of the dTDP-L-rhamnose synthesis pathway, from Salmonella enterica serovar Typhimurium [26].
• From the reaction with 20 ml volume, approximately 180 mg of dTDP-L-rhamnose was obtained in an overall yield of 60% after two-step purification, that is, anion exchange chromatography and gel filtration for desalting [27].
• Furthermore, an HPLC technique is presented for determining the net activity of dTDP-6-deoxy-D-xylo-4-hexulose 3,5-epimerase and NADPH:dTDP-6-deoxy-L-lyxo-4-hexulose-4-reductase, based on separation of dTDP-6-deoxy-D-xylo-4-hexulose and dTDP-L-rhamnose [28].

References