Words similar to midas
Example sentences for: midas
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One possibility is that the MIDAS site serves to attach protein ligands through a mechanism involving participation of a glutamate or aspartate residue on the ligand in the coordination of a Mg 2+ion at the MIDAS site of midasin, in a manner similar to that by which the MIDAS site in integrin I-domains appears to mediate attachment of collagen through the glutamate in the GFOGER binding motif [ 36 ] . Interestingly, the related RGE ligand-binding motif [ 41 ] occurs in a conserved region of the midasin AAA-domain (yeast, residues 1835-1838), as well as in the AAA-domain of Mg chelatases [ 32 ] . The presence of this consensus binding motif in the AAA domain raises the possibility of the midasin molecule folding back onto itself, with the M-domain becoming attached to one face of the AAA domain and perhaps regulating access to its central chamber, in a manner analogous to that in which the 19S proteasome regulator, also an AAA protein, controls access to the central proteolytic chamber of the proteasome [ 42 ] .
The residues in the MIDAS motifs lie on three closely apposed loops located on the upper edge of the β-sheet, where they form the metal-binding site, with oxygen atoms in the aspartate, serine and threonine residues coordinating the metal ion [ 9 ] . In integrin α2β1, which is a collagen receptor, the metal-binding site also binds the collagen ligand through the conserved glutamate in a GFOGER motif (O = hydroxyproline) completing the coordination sphere of the metal [ 28 ] . In vivo, the binding of collagen at this site appears to be regulated through a conformational shift in which the loops forming the MIDAS site change from a closed to an open conformation [ 29 30 31 ] . Other proteins containing a domain with all three MIDAS motifs include the D-subunit of magnesium chelatase [ 32 ] , Ca-activated chloride-channel protein [ 33 34 ] , nitrate reductase (accession AAC79447), and the D subunit of nitric oxide reductase (accession AAC45374).
The initial step of the insertion can proceed in the presence of either Mg.ATP or a non-hydrolyzable ATP-analog and involves oligomerization of the BchD and BchI subunits to form an oligomeric ring of AAA protomers that resembles the ring structure of NSF and other AAA proteins [ 14 32 ] . The second step of the insertion involves an obligatory hydrolysis of ATP that is tightly coupled with the transfer of the chelated Mg 2+to the protoporphyrin ring by BchH [ 49 ] . Although the details differ from midasin, particularly with respect to the subunit composition of the AAA ring, this chelation reaction provides a structural model suggesting that the function of the midasin M-domain may be to regulate the ATPase activity of the AAA protomers in the pseudo-hexameric ring and thus couple ATP hydrolysis to the binding of a protein ligand at the MIDAS site.
All the MIDAS sequence motifs in this domain are retained and most of the residues in the highly conserved NH 2 -extension of the M-domain are unaffected.
The D/E-rich domain is followed by the COOH-terminal M-domain that is highly conserved and contains a set of MIDAS sequence motifs [ 9 ] .
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