Dataset Information

Heme axial methionine fluxionality in Hydrogenobacter thermophilus cytochrome c552.

ABSTRACT: The heme group in paramagnetic (S = 1/2) ferricytochromes c typically displays a markedly asymmetric distribution of unpaired electron spin density among the heme pyrrole beta substituents. This asymmetry is determined by the orientations of the heme axial ligands, histidine and methionine. One exception to this is ferricytochrome c(552) from Hydrogenobacter thermophilus, which has similar amounts of unpaired electron spin density at the beta substituents on all four heme pyrroles. Here, determination of the orientation of the magnetic axes and analysis of NMR line shapes for H. thermophilus ferricytochrome c(552) is performed. These data reveal that the unusual electronic structure for this protein is a result of fluxionality of the heme axial methionine. It is proposed that the ligand undergoes inversion at the pyramidal sulfur, and the rapid interconversion between two diastereomeric forms results in the unusual heme electronic structure. Thus a fluxional process for a metal-bound amino acid side chain has now been identified.

SUBMITTER: Zhong L

PROVIDER: S-EPMC423247 | biostudies-literature | 2004 Jun

REPOSITORIES: biostudies-literature

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Publications

Heme axial methionine fluxionality in Hydrogenobacter thermophilus cytochrome c552.

Zhong Linghao L Wen Xin X Rabinowitz Terry M TM Russell Brandy S BS Karan Elizabeth F EF Bren Kara L KL

Proceedings of the National Academy of Sciences of the United States of America 20040525 23

The heme group in paramagnetic (S = 1/2) ferricytochromes c typically displays a markedly asymmetric distribution of unpaired electron spin density among the heme pyrrole beta substituents. This asymmetry is determined by the orientations of the heme axial ligands, histidine and methionine. One exception to this is ferricytochrome c(552) from Hydrogenobacter thermophilus, which has similar amounts of unpaired electron spin density at the beta substituents on all four heme pyrroles. Here, determi ...[more]

PMID: 15161973

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Project description:Hydrogenobacter thermophilus is an obligate chemolithoautotrophic bacterium of the phylum Aquificae and is capable of fixing carbon dioxide through the reductive tricarboxylic acid (TCA) cycle. The recent discovery of two novel-type phosphoserine phosphatases (PSPs) in H. thermophilus suggests the presence of a phosphorylated serine biosynthesis pathway; however, the physiological role of these novel-type metal-independent PSPs (iPSPs) in H. thermophilus has not been confirmed. In the present study, a mutant strain with a deletion of pspA, the catalytic subunit of iPSPs, was constructed and characterized. The generated mutant was a serine auxotroph, suggesting that the novel-type PSPs and phosphorylated serine synthesis pathway are essential for serine anabolism in H. thermophilus. As an autotrophic medium supplemented with glycine did not support the growth of the mutant, the reversible enzyme serine hydroxymethyltransferase does not appear to synthesize serine from glycine and may therefore generate glycine and 5,10-CH2-tetrahydrofolate (5,10-CH2-THF) from serine. This speculation is supported by the lack of glycine cleavage activity, which is needed to generate 5,10-CH2-THF, in H. thermophilus Determining the mechanism of 5,10-CH2-THF synthesis is important for understanding the fundamental anabolic pathways of organisms, because 5,10-CH2-THF is a major one-carbon donor that is used for the synthesis of various essential compounds, including nucleic and amino acids. The findings from the present experiments using a pspA deletion mutant have confirmed the physiological role of iPSPs as serine producers and show that serine is a major donor of one-carbon units in H. thermophilusIMPORTANCE Serine biosynthesis and catabolism pathways are intimately related to the metabolism of 5,10-CH2-THF, a one-carbon donor that is utilized for the biosynthesis of various essential compounds. For this reason, determining the mechanism of serine synthesis is important for understanding the fundamental anabolic pathways of microorganisms. In the present study, we experimentally confirmed that a novel phosphoserine phosphatase in the obligate chemolithoautotrophic bacterium Hydrogenobacter thermophilus is essential for serine biosynthesis. This finding indicates that serine is synthesized from an intermediate of gluconeogenesis in H. thermophilus In addition, because glycine cleavage system activity and genes encoding an enzyme capable of producing 5,10-CH2-THF were not detected, serine appears to be the major one-carbon donor to tetrahydrofolate (THF) in H. thermophilus.

Dataset Information

Heme axial methionine fluxionality in Hydrogenobacter thermophilus cytochrome c552.

Publications

Heme axial methionine fluxionality in Hydrogenobacter thermophilus cytochrome c552.

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