MgATP regulates allostery and fiber formation in IMPDHs

INSERM, U1054, Centre de Biochimie Structurale, F-34090 Montpellier, France.
Structure (Impact Factor: 5.62). 04/2013; 21(6). DOI: 10.1016/j.str.2013.03.011
Source: PubMed


Inosine-5'-monophosphate dehydrogenase (IMPDH) is a rate-limiting enzyme in nucleotide biosynthesis studied as an important therapeutic target and its complex functioning in vivo is still puzzling and debated. Here, we highlight the structural basis for the regulation of IMPDHs by MgATP. Our results demonstrate the essential role of the CBS tandem, conserved among almost all IMPDHs. We found that Pseudomonas aeruginosa IMPDH is an octameric enzyme allosterically regulated by MgATP and showed that this octameric organization is widely conserved in the crystal structures of other IMPDHs. We also demonstrated that human IMPDH1 adopts two types of complementary octamers that can pile up into isolated fibers in the presence of MgATP. The aggregation of such fibers in the autosomal dominant mutant, D226N, could explain the onset of the retinopathy adRP10. Thus, the regulatory CBS modules in IMPDHs are functional and they can either modulate catalysis or macromolecular assembly.

Download full-text


Available from: Hélène Munier-Lehmann, Dec 19, 2013
31 Reads
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Cystathionine β-synthase (CBS) domains or CBS motifs are conserved structural domains that are present in thousands of non functionally-related proteins from all kingdoms of life. Their importance is underlined by the range of hereditary diseases associated with mutations in their amino acid sequence. CBS motifs associate in pairs referred to as Bateman modules. In contrast with initial assumptions, it is now well documented that CBS motifs and/or Bateman modules may suffer conformational changes upon binding of adenosine derivatives, metal ions or nucleic acids. The degree and direction of these structural changes depend on the type of ligand, the intrinsic features of the binding sites and the association manner of the Bateman modules. This review aims to provide a summary of the current knowledge on the structural basis of ligand recognition and on the structural effects caused by these ligands in CBS domain containing proteins.
    Archives of Biochemistry and Biophysics 10/2013; 540(1-2). DOI:10.1016/ · 3.02 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Ancient conserved domain protein/cyclin M (CNNM) family proteins are evolutionarily conserved Mg(2+) transporters. However, their biochemical mechanism of action remains unknown. Here, we show the functional importance of the commonly conserved cystathionine-β-synthase (CBS) domains and reveal their unique binding ability to ATP. Deletion mutants of CNNM2 and CNNM4, lacking the CBS domains, are unable to promote Mg(2+)-efflux. Furthermore, the substitution of one amino acid residue in the CBS domains of CNNM2, which is associated with human hereditary hypomagnesaemia, abrogates Mg(2+)-efflux. Binding analyses reveal that the CBS domains of CNNM2 directly bind to ATP and not AMP in a manner dependent on the presence of Mg(2+), which is inhibited in a similar pattern by the disease-associated amino acid substitution. The requirement of Mg(2+) for these interactions is a unique feature among CBS domains, which can be explained by the presence of highly electronegative surface potentials around the ATP-binding site on CNNM2. These results demonstrate that the CBS domains play essential roles in Mg(2+)-efflux, probably through interactions with ATP. Interactions with ATP, which mostly forms complexes with Mg(2+) in cells, may account for the rapid Mg(2+) transport by CNNM family proteins.
    Journal of Biological Chemistry 04/2014; 289(21). DOI:10.1074/jbc.M114.551176 · 4.57 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Regulated family II pyrophosphatases (CBS-PPases) contain a nucleotide-binding insert comprising a pair of cystathionine β-synthase (CBS) domains, termed a Bateman module. By binding with high affinity to the CBS domains, AMP and ADP usually inhibit the enzyme, whereas ATP activates it. Here, we demonstrate that AMP, ADP, and ATP bind in a positively cooperative manner to CBS-PPases from four bacteria: Desulfitobacterium hafniense, Clostridium novyi, Clostridium perfringens, and Eggerthella lenta. Enzyme interaction with substrate as characterized by the Michaelis constant (Km) also exhibited positive catalytic cooperativity that decreased in magnitude upon nucleotide binding. The degree of both types of cooperativity increased with increasing concentration of the cofactor Mg2+ except for the C. novyi PPase where Mg2+ produced the opposite effect on kinetic cooperativity. Further exceptions from these general rules were ADP binding to C. novyi PPase and AMP binding to E. lenta PPase, neither of which had any effect on activity. A genetically engineered deletion variant of D. hafniense PPase lacking the regulatory insert was fully active but differed from the wild-type enzyme in that it was insensitive to nucleotides and bound substrate non-cooperatively and with a smaller Km value. These results indicate that the regulatory insert acts as an internal inhibitor and confers dual positive cooperativity to CBS domain-containing PPases, making them highly sensitive regulators of the PPi level in response to the changes in cell energy status that control adenine nucleotide distribution. These regulatory features may be common among other CBS domain-containing proteins.
    Journal of Biological Chemistry 07/2014; 289(33). DOI:10.1074/jbc.M114.589473 · 4.57 Impact Factor
Show more