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Isolation and structure of mycobactin T, a growth factor from Mycobacterium tuberculosis.

ABSTRACT: 1. A growth factor for Mycobacterium johnei has been isolated from Mycobacterium tuberculosis as an iron complex; it has been named ferric mycobactin T. 2. Ferric mycobactin T as isolated is a mixture of at least four closely related components differing only in their fatty acid side chains. 3. Mycobactin T resembles mycobactin P in structure but differs in the following respects: (a) the aromatic acid residue is salicylic acid in place of 2-hydroxy-6-methylbenzoic acid; (b) the hydroxy acid residue is (+)-beta-hydroxybutyric acid in place of (-)-3-hydroxy-2-methylpentanoic acid; (c) its components have fatty acid side chains that are mostly different from the side chains of the components in mycobactin P preparations. One minor component in mycobactin T has probably a cis-octadec-2-enoyl side chain. The major side-chain components correspond to acids of chain length C(18)-C(21) that are not n-saturated or n-Delta(2)-unsaturated acids. 4. The differences in biosynthesis between mycobactins T and P are discussed.

SUBMITTER: Snow GA

PROVIDER: S-EPMC1264557 | biostudies-other | 1965 Oct

REPOSITORIES: biostudies-other

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Project description:BackgroundMembers of the WhiB-like (Wbl) protein family possess iron-sulfur clusters and are implicated in the regulation of developmental processes in Actinomycetes. Mycobacterium tuberculosis possesses seven Wbl proteins. The [4Fe-4S] cluster of M. tuberculosis WhiB1 is relatively insensitive to O(2) but very sensitive to nitric oxide (NO). Nitric oxide nitrosylates the WhiB1 iron-sulfur cluster and promotes DNA-binding; the apo-forms of WhiB1 also bind DNA. However, the molecular requirements for iron-sulfur cluster acquisition and for DNA-binding by WhiB1 are poorly characterized.Methods and findingsWhiB1 variants were created by site-directed mutagenesis and the abilities of the corresponding proteins to acquire an iron-sulfur cluster and/or bind to whiB1 promoter DNA were assessed. All four Cys residues (Cys9, 37, 40, and 46) in the N-terminal region of WhiB1 were required for incorporation of a [4Fe-4S] cluster, whereas a possible alternative cluster ligand Asp13 (by analogy with M. smegmatis WhiB2) was not. The C-terminal region of WhiB1 is predicted to house the DNA-binding domain of the protein consisting of a predicted β-turn ((58)GVWGG(62)) followed by two amino acid motifs ((72)KRRN(75) and (78)TKAR(81)) that are conserved in WhiB1 proteins. Gly residues (Gly58, 61 and 62) in the β-turn and positively-charged residues (Lys72, Arg73, Arg74, Lys79 and Arg81) in the downstream conserved regions were required for binding of WhiB1 DNA.ConclusionsSite-directed mutagenesis of M. tuberculosis whiB1 and characterization of the corresponding proteins has been used to explore structure-function relationships of the NO-responsive transcription factor WhiB1. This showed that all four conserved Cys residues in the N-terminal region are required for incorporation of iron-sulfur clusters but not for DNA-binding. Analysis of variants with amino acid substitutions in the C-terminal region revealed the crucial roles played by a predicted β-turn and two conserved positively-charged motifs in facilitating DNA-binding, but not iron-sulfur cluster acquisition, by WhiB1.

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Isolation and structure of mycobactin T, a growth factor from Mycobacterium tuberculosis.

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