Trends in Plant Science
ReviewOrganellar peptide deformylases: universality of the N-terminal methionine cleavage mechanism
Section snippets
Incorporation of N-formylmethionine into proteins synthesized in organelles
Cytosolic translation is generally initiated at the first AUG codon of plant mRNAs (Ref. 4), although exceptions to this rule have been described in Arabidopsis 5. This contrasts with the situation in organelles, in which translation initiation depends on the presence of a ribosome-binding site in the vicinity of the start codon, usually AUG but also occasionally GUG (Ref. 6). In the two organelles with expressed genomes in plants (plastids and mitochondria), the process of translation
N-terminal methionine cleavage in plants occurs in the cytosol and in the organelles
In the cytosol of eubacteria, mammals and fungi, the initiator methionine of mature proteins is removed in two-thirds of cases 11, 12, 13. The pathway leading to methionine removal involves methionine aminopeptidase (MAP) activity. Two classes of MAPs have been described (MAP1 and MAP2) 11. The two MAP classes have convergent three-dimensional structures but low levels of sequence identity. Eubacteria have one or more MAP1s, whereas eukaryotes have at least one MAP1 and one MAP2. MAP1 and MAP2
N-terminal methionine excision machinery in higher plants
Recently, on the basis of homology with the bacterial system, cDNAs and/or genes encoding several proteins of the N-terminal methionine removal machinery have been identified in higher plants (monocots and dicots) and the proteins partially characterized 3. In Arabidopsis, this nuclear-encoded machinery includes two class 1 peptide deformylases (PDF1A and PDF1B), four MAP1s (MAP1A, MAP1B, MAP1C and MAP1D) and two MAP2s (MAP2A and MAP2B). Except for MAP1A and the two MAP2s, the identified
N-terminal methionine cleavage and chloroplast function
Investigations of the function of N-terminal methionine cleavage have been hampered by the essential nature of the process. Gene inactivation experiments carried out in bacteria 28, 29 and yeast 30 led to cell death. By contrast, plastid protein synthesis is not essential because it can be specifically blocked with antibiotics such as streptomycin 8. It is therefore tempting to use the plastid as a model system to study the role of N-terminal methionine cleavage. Actinonin was recently shown to
Methionine cleavage is universal in organelles
The availability of complete genome sequences for several eukaryotes enables us to re-examine the question of the universality of the N-terminal methionine cleavage mechanism in organelles. Clearly, the yeast S. cerevisiae and the worm C. elegans lack this machinery. However, it now appears that they might be exceptions. Indeed, PDF homologues are present in vertebrates, insects and various unicellular eukaryotes 3, 41 (Fig. 3), including mycetozoa (the amoeba Dictyostelium discoideum has one
Perspectives
Studies of the plant system were the first step towards a demonstration of the universality of the N-terminal methionine cleavage mechanism and the occurrence of PDF orthologues in most living things. Plants appear to be excellent model systems for investigating the function of N-terminal methionine cleavage, a mechanism that is still poorly understood. The major advantages of plant cells lie in the small number of proteins encoded by the genomes of each of the organelles and the wealth of
Acknowledgements
We are greatly indebted to Jacques Joyard (CEA, Grenoble) and Olivier Vallon (IBPC, Paris) for their critical reading and improvement of the manuscript. We wish to thank all our collaborators in Gif/Yvette who have collectively contributed to our work. Our work was supported by ATIPE, PCV and MCT grants from the CNRS to T.M. and by the Fondation pour la Recherche Médicale. C.G. was supported by a postdoctoral fellowship from the Association pour la Recherche sur le Cancer (ARC, Villejuif,
References (50)
Methionine as translation start signal: a review of the enzymes of the pathway in Escherichia coli
Biochimie
(1993)A cDNA for nuclear-encoded chloroplast translational initiation factor 2 from a higher plant is able to complement an infB Escherichia coli null-mutant
J. Biol. Chem.
(2001)- et al.
Aminoacylation of Phaseolus vulgaris cytoplasmic, chloroplastic and mitochondrial tRNAsMet and of Escherichia coli tRNAsMet by homologous and heterologous enzymes
Biochim. Biophys. Acta
(1975) N-terminal processing: the methionine aminopeptidase and N alpha-acetyl transferase families
Trends Biochem. Sci.
(1998)The specificities of yeast methionine aminopeptidase and acetylation of amino-terminal methionine in vivo. Processing of altered iso-1-cytochromes c created by oligonucleotide transformation
J. Biol. Chem.
(1990)- et al.
Purification and sequencing of cytochrome b from potato reveals methionine cleavage of a mitochondrially encoded protein
FEBS Lett.
(1993) Transit peptides play a major role in the preferential import of proteins into leucoplasts and chloroplasts
J. Biol. Chem.
(1996)Sequence of the leader peptidase gene of Escherichia coli and the orientation of leader peptidase in the bacterial envelope
J. Biol. Chem.
(1983)- et al.
The amino terminus of the aspartate chemoreceptor is formylmethionine
J. Biol. Chem.
(1990) - et al.
N-terminal amino acid sequences of the subunits of the Na+-translocating F1F0 ATPase from Propionigenium modestum
FEBS Lett.
(1993)