Figure 3

Sequence alignment of the six AAA protomers in midasin from humans, yeast and Giardia The alignment shows two aspects of sequence conservation: (1) the level of conservation for each single AAA protomer compared to the same protomer in other organisms; (2) the level of conservation between the six AAA protomers (AAA1, AAA2, AAA3, AAA4, AAA5, AAA6) compared one against another. The Motif line above the alignment indicates the sequence motifs that characterize members of the AAA ATPase family [5]. All AAA motifs occur in regions of relatively well-conserved sequence, with the exception of Box II (not shown) which is poorly conserved in midasin. Critical residues interacting with bound nucleotide in other AAA proteins are indicated by: ▲, residues in the Walker A and B motifs required for binding and hydrolysis of ATP [17]; ●, Asn in sensor 1 and Arg in sensor 2 believed to sense the γ-phosphate status [5]; ■, Asp and Arg in Boxes VI and VII that are believed to sense the γ-phosphate status in adjacent protomers of the hexameric structure [6, 15, 18]. The Structure line below the alignment indicates the secondary structural elements corresponding to the sequence motifs in other AAA ATPases whose structures have been resolved at the atomic level [5]. Colors indicate level of consensus for each residue position. In this context, consensus is defined as sequence conservation of a single AAA protomer in the three organisms analyzed; it does not refer to comparisons between different AAA protomers. Color key: red/yellow, invariant; blue/blue, majority consensus of identical residues; green/green, majority consensus of highly conserved residues; green/white, weakly conserved residues; gray/white, non-conserved residues. Organisms : HUMAN, Homo sapiens; SACCE: Sacchararomyces cerevisiae; GIARD, Giardia intestinalis.