Multiple pathways for isoleucine biosynthesis in the spirochete Leptospira

Abstract

Spirochetes of the genus Leptospira have previously been shown to use an unusual pathway to synthesize isoleucine. For reasons of convenience, we assume that only one unusual pathway is found in the genus, and we refer to it as the pyruvate pathway. We determined the distribution of this pyruvate pathway in representatives of the seven Leptospira DNA hybridization groups. Our method included labeling the representative strains with radioactive carbon dioxide and other radioactive precursors, fractionating the cells, and determining the specific activities (counts detected per nanomole) of the amino acids found in the protein fractions. On the basis of isoleucine biosynthesis, we found that the genus can be classified as follows: class I primarily, if not exclusively, uses the well-known threonine pathway; class II uses mostly the pyruvate pathway, with a minor amount of isoleucine being synthesized via the threonine pathway; and class III uses the pyruvate pathway exclusively. No relationship appears to exist between the degree of DNA hybridization and the classes of isoleucine biosynthesis. Although the precise intermediates on the pyruvate pathway are unknown, the origin of the carbon skeleton of isoleucine synthesized by this pathway is consistent with a borrowing of the leucine biosynthetic enzymes. However, we found that the pyruvate pathway is not controlled by leucine and that the two isoleucine pathways are independently regulated. Finding major and highly evolved multiple biosynthetic pathways of a specific amino acid within one genus is unique, and, conceivably, represents phylogenetic diversity within Leptospira.

( R )-Citramalate Synthase in Methanogenic Archaea

“…Among these is the formation of isoleucine via the pyruvate pathway, which, based on 13 C nuclear magnetic resonance labeling studies (7)(8)(9)15), is the major pathway for isoleucine formation in many species of methanogenic archaea. Labeling studies in other organisms have produced similar results (4,23).…”

Changes in Free Amino Acid Content in ‘Jonagold’ Apple Fruit as Related to Branched-chain Ester Production, Ripening, and Senescence

“…A second pathway has been found in yeast in which cystathionine-g-lyase (Cys3) produces a-ketobutyrate from cystathionine through cysteine biosynthesis (Ono et al, 1999). The third pathway for isoleucine biosynthesis has been described in Methanococcus jannaschii and Leptospira interrogans bacteria (Drevland et al, 2007;Howell et al, 1999;Westfall et al, 1983;Xu et al, 2004). In this pathway, acetyl-CoA and pyruvate are substrates for the formation of citramalic acid by citramalate synthase (CIM), which is a member of the IPMS family (Fig.…”

A comprehensive survey on isoleucine biosynthesis pathways in seven epidemicLeptospira interrogansreference strains of China

“…This result clearly indicated that the metabolic pathways used for isoleucine biosynthesis are likely an additional physiological marker, that could be used to distinguish the pathogenic L. interrogans versus the saprophytic leptospires, such as L. biflexa and L. meyeri. Westfall et al (1983) performed the pioneering work on a similar survey on isoleucine biosynthetic pathways, i.e. threonine, pyruvate or a combination of both pathways and concluded that there was no correlation between the degree of DNA hybridization of the Leptospira species and their isoleucine biosynthetic pathways.…”

“…However, Charon et al (1974) studied the biosynthesis of isoleucine in Leptospira using radiotracers and suggested a metabolic pattern distinct from most other bacteria. Exploring the isoleucine biosynthesis pathways in seven representative strains of Leptospira, Westfall et al (1983) found that besides the strains using predominantly the pyruvate pathway, with a minor utilization of the threonine pathway, others use one of the two pathways exclusively. A recent study demonstrated the details of the pyruvate pathway exclusively used by L. interrogans serovar Lai strain 56601 for its isoleucine biosynthesis (Xu et al, 2004).…”