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Expression and genomic analysis of midasin, a novel and highly conserved AAA protein distantly related to dynein.

Garbarino JE, Gibbons IR - BMC Genomics (2002)

Bottom Line: Expression of hemagglutamin-tagged midasin in yeast demonstrates a polypeptide of the anticipated size that is localized principally in the nucleus.The highly conserved structure of midasin in eukaryotes, taken in conjunction with its nuclear localization in yeast, suggests that midasin may function as a nuclear chaperone and be involved in the assembly/disassembly of macromolecular complexes in the nucleus.The AAA domain of midasin is evolutionarily related to that of dynein, but it appears to lack a microtubule-binding site.

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Affiliation: Molecular and Cell Biology Department, University of California Berkeley, 94720-3200, USA. joangarb@uclink4.berkeley.edu

ABSTRACT

Background: The largest open reading frame in the Saccharomyces genome encodes midasin (MDN1p, YLR106p), an AAA ATPase of 560 kDa that is essential for cell viability. Orthologs of midasin have been identified in the genome projects for Drosophila, Arabidopsis, and Schizosaccharomyces pombe.

Results: Midasin is present as a single-copy gene encoding a well-conserved protein of approximately 600 kDa in all eukaryotes for which data are available. In humans, the gene maps to 6q15 and encodes a predicted protein of 5596 residues (632 kDa). Sequence alignments of midasin from humans, yeast, Giardia and Encephalitozoon indicate that its domain structure comprises an N-terminal domain (35 kDa), followed by an AAA domain containing six tandem AAA protomers (approximately 30 kDa each), a linker domain (260 kDa), an acidic domain (approximately 70 kDa) containing 35-40% aspartate and glutamate, and a carboxy-terminal M-domain (30 kDa) that possesses MIDAS sequence motifs and is homologous to the I-domain of integrins. Expression of hemagglutamin-tagged midasin in yeast demonstrates a polypeptide of the anticipated size that is localized principally in the nucleus.

Conclusions: The highly conserved structure of midasin in eukaryotes, taken in conjunction with its nuclear localization in yeast, suggests that midasin may function as a nuclear chaperone and be involved in the assembly/disassembly of macromolecular complexes in the nucleus. The AAA domain of midasin is evolutionarily related to that of dynein, but it appears to lack a microtubule-binding site.

No MeSH data available.


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Sequence alignment of the AAA protomers in midasin with those in other branches of AAA-ATPase family The alignment is limited to residues contained in the P-loop, Walker B, and sensor 1 motifs of AAA2 and AAA3 protomers of midasin from humans and yeast, together with the corresponding residues in the AAA1 protomer of cytoplasmic dynein [6], and in a variety of other AAA proteins. The positions and lengths of the P-loop, Walker B, and sensor 1 motifs are taken from the review of Neuwald et al [5]. The color used for each residue in the alignment indicates its similarity to that present at the corresponding position in yeast cytoplasmic dynein. Color key: Yellow/red, all AAA proteins shown have identical residue; blue/blue, identical to AAA1 of dynein; green/green, closely similar to AAA1 of dynein; green/white, moderately similar; gray/white, not similar.
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Figure 7: Sequence alignment of the AAA protomers in midasin with those in other branches of AAA-ATPase family The alignment is limited to residues contained in the P-loop, Walker B, and sensor 1 motifs of AAA2 and AAA3 protomers of midasin from humans and yeast, together with the corresponding residues in the AAA1 protomer of cytoplasmic dynein [6], and in a variety of other AAA proteins. The positions and lengths of the P-loop, Walker B, and sensor 1 motifs are taken from the review of Neuwald et al [5]. The color used for each residue in the alignment indicates its similarity to that present at the corresponding position in yeast cytoplasmic dynein. Color key: Yellow/red, all AAA proteins shown have identical residue; blue/blue, identical to AAA1 of dynein; green/green, closely similar to AAA1 of dynein; green/white, moderately similar; gray/white, not similar.

Mentions: The early evolutionary divergence of the different major branches of the AAA family makes it difficult to evaluate the phylogenetic relationships among them [45]. However, by restricting the analysis to residues in the more highly conserved regions of the AAA structure that interact directly with ATP, we have been able to improve the signal to noise ratio sufficiently to probe the phylogenetic relationship of midasin and dynein to representative members in other branches of the AAA family. Such analysis of the AAA protomers that are best conserved among organisms (AAA2, AAA3, AAA4 and AAA5 in midasin, and AAA1 in dynein) shows that the AAA protomers of midasin and dynein are substantially more closely related to each other than they are to those in the other branches of the AAA family examined (Figs 7, 8). This result supports the view that midasin and dynein evolved from a common AAA ancestral protein that had already developed a subunit structure of six AAA protomers in a single polypeptide. However, insufficient information exists to relate this last common ancestor to any particular other branch of the presently existing AAA family.


Expression and genomic analysis of midasin, a novel and highly conserved AAA protein distantly related to dynein.

Garbarino JE, Gibbons IR - BMC Genomics (2002)

Sequence alignment of the AAA protomers in midasin with those in other branches of AAA-ATPase family The alignment is limited to residues contained in the P-loop, Walker B, and sensor 1 motifs of AAA2 and AAA3 protomers of midasin from humans and yeast, together with the corresponding residues in the AAA1 protomer of cytoplasmic dynein [6], and in a variety of other AAA proteins. The positions and lengths of the P-loop, Walker B, and sensor 1 motifs are taken from the review of Neuwald et al [5]. The color used for each residue in the alignment indicates its similarity to that present at the corresponding position in yeast cytoplasmic dynein. Color key: Yellow/red, all AAA proteins shown have identical residue; blue/blue, identical to AAA1 of dynein; green/green, closely similar to AAA1 of dynein; green/white, moderately similar; gray/white, not similar.
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Related In: Results  -  Collection

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Figure 7: Sequence alignment of the AAA protomers in midasin with those in other branches of AAA-ATPase family The alignment is limited to residues contained in the P-loop, Walker B, and sensor 1 motifs of AAA2 and AAA3 protomers of midasin from humans and yeast, together with the corresponding residues in the AAA1 protomer of cytoplasmic dynein [6], and in a variety of other AAA proteins. The positions and lengths of the P-loop, Walker B, and sensor 1 motifs are taken from the review of Neuwald et al [5]. The color used for each residue in the alignment indicates its similarity to that present at the corresponding position in yeast cytoplasmic dynein. Color key: Yellow/red, all AAA proteins shown have identical residue; blue/blue, identical to AAA1 of dynein; green/green, closely similar to AAA1 of dynein; green/white, moderately similar; gray/white, not similar.
Mentions: The early evolutionary divergence of the different major branches of the AAA family makes it difficult to evaluate the phylogenetic relationships among them [45]. However, by restricting the analysis to residues in the more highly conserved regions of the AAA structure that interact directly with ATP, we have been able to improve the signal to noise ratio sufficiently to probe the phylogenetic relationship of midasin and dynein to representative members in other branches of the AAA family. Such analysis of the AAA protomers that are best conserved among organisms (AAA2, AAA3, AAA4 and AAA5 in midasin, and AAA1 in dynein) shows that the AAA protomers of midasin and dynein are substantially more closely related to each other than they are to those in the other branches of the AAA family examined (Figs 7, 8). This result supports the view that midasin and dynein evolved from a common AAA ancestral protein that had already developed a subunit structure of six AAA protomers in a single polypeptide. However, insufficient information exists to relate this last common ancestor to any particular other branch of the presently existing AAA family.

Bottom Line: Expression of hemagglutamin-tagged midasin in yeast demonstrates a polypeptide of the anticipated size that is localized principally in the nucleus.The highly conserved structure of midasin in eukaryotes, taken in conjunction with its nuclear localization in yeast, suggests that midasin may function as a nuclear chaperone and be involved in the assembly/disassembly of macromolecular complexes in the nucleus.The AAA domain of midasin is evolutionarily related to that of dynein, but it appears to lack a microtubule-binding site.

View Article: PubMed Central - HTML - PubMed

Affiliation: Molecular and Cell Biology Department, University of California Berkeley, 94720-3200, USA. joangarb@uclink4.berkeley.edu

ABSTRACT

Background: The largest open reading frame in the Saccharomyces genome encodes midasin (MDN1p, YLR106p), an AAA ATPase of 560 kDa that is essential for cell viability. Orthologs of midasin have been identified in the genome projects for Drosophila, Arabidopsis, and Schizosaccharomyces pombe.

Results: Midasin is present as a single-copy gene encoding a well-conserved protein of approximately 600 kDa in all eukaryotes for which data are available. In humans, the gene maps to 6q15 and encodes a predicted protein of 5596 residues (632 kDa). Sequence alignments of midasin from humans, yeast, Giardia and Encephalitozoon indicate that its domain structure comprises an N-terminal domain (35 kDa), followed by an AAA domain containing six tandem AAA protomers (approximately 30 kDa each), a linker domain (260 kDa), an acidic domain (approximately 70 kDa) containing 35-40% aspartate and glutamate, and a carboxy-terminal M-domain (30 kDa) that possesses MIDAS sequence motifs and is homologous to the I-domain of integrins. Expression of hemagglutamin-tagged midasin in yeast demonstrates a polypeptide of the anticipated size that is localized principally in the nucleus.

Conclusions: The highly conserved structure of midasin in eukaryotes, taken in conjunction with its nuclear localization in yeast, suggests that midasin may function as a nuclear chaperone and be involved in the assembly/disassembly of macromolecular complexes in the nucleus. The AAA domain of midasin is evolutionarily related to that of dynein, but it appears to lack a microtubule-binding site.

No MeSH data available.


Related in: MedlinePlus