Allelic characterization of the leaf-variegated mutation var2 identifies the conserved amino acid residues of FtsH that are important for ATP hydrolysis and proteolysis.
Arabidopsis var1 and var2 mutants exhibit leaf variegation. VAR1 and VAR2 encode similar FtsH metalloproteases (FtsH5 and FtsH2, respectively). We have previously found many variegated mutants to be allelic to var2. Each mutant was shown to express a different degree of variegation, and the formation of white sectors was enhanced in severely variegated alleles when these alleles were grown at low temperature. VAR1/FtsH5 and VAR2/FtsH2 levels were mutually affected even in the weak alleles, confirming our previous observation that the two proteins form a hetero complex. In this study, the sites of the mutations in these var2 alleles were determined. We isolated eight point mutations. Five alleles resulted in an amino acid substitution. Three of the five amino acid substitutions occurred in Walker A and B motifs of the ATP-binding site, and one occurred in the central pore motif. These mutations were considered to profoundly suppress the ATPase and protease activities. In contrast, one mutation was found in a region that contained no obvious signature motifs, but a neighboring sequence, Gly-Ala-Asp, was highly conserved among the members of the AAA protein family. Site-directed mutagenesis of the corresponding residue in E. coli FtsH indeed showed that this residue is necessary for proper ATP hydrolysis and proteolysis. Based on these results, we propose that the conserved Gly-Ala-Asp motif plays an important role in FtsH activity. Thus, characterization of the var2 alleles could help to identify the physiologically important domain of FtsH.
Sakamoto
Wataru
W
Research Institute for Bioresources, Okayama University, 2-20-1 Chuo, Kurashiki, Okayama 710-0046, Japan. saka@rib.okayama-u.ac.jp
Miura
Eiko
E
Kaji
Yumiko
Y
Okuno
Takashi
T
Nishizono
Masayo
M
Ogura
Teru
T
D049069:ATP-Dependent Proteases; D000251:Adenosine Triphosphatases / Q000235:genetics / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism*; D000483:Alleles; D020816:Amino Acid Motifs / Q000235:genetics; D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D017124:Conserved Sequence / Q000235:genetics; D004252:DNA Mutational Analysis; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005816:Genetic Complementation Test; D015151:Immunoblotting; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D045726:Metalloproteases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D020125:Mutation, Missense; D010641:Phenotype; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D049069:ATP-Dependent Proteases; D000251:Adenosine Triphosphatases; D000255:Adenosine Triphosphate; D029681:Arabidopsis Proteins; D018744:DNA, Plant; D007527:Isoenzymes; D008565:Membrane Proteins; D045726:Metalloproteases; C402651:AT2G30950 protein, Arabidopsis