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![[Figure 1]](kw5089fig1mag.jpg)
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Figure 1
(a) Overlay of all eight chains from the four structures, as well as the two chains of the previously published structure (PDB entry 3q2o) of baPurK. Most of the structural elements, including the major ligand-interacting loops, the J-loop (cyan), P-loop (red) and Ω-loop (yellow), exhibit little movement, with the exceptions being the A-loop (green), the B-loop (blue) and the ABC-loop (orange). The B-loop is the most flexible and is in an `open' conformation or `up' position without ATP but is in a `closed' conformation or `down' position with ATP (see top inset; the `open' conformation is from 3q2o chain B and the `closed' conformation is from 3v4s chain B). (b) The volume of the active site with ATP, Mg2+ and HCO3− (3v4s chain B) is approximately 1900 Å3, as generated by the Pocket-Finder server, and is shown as a blue space-filled pocket. (c) The electrostatic potential of the sites for AIR, HCO3− and the phosphates of ATP is highly positive (blue), while the rest of the surface is mostly negative (red) or neutral (white). The arrow shows the active-site tunnel. The tail of the arrow shows the site to which the adenine ring of ATP binds and the head of the arrow shows the site to which AIR binds, with HCO3− in between ATP and AIR. The circled region consists of a cluster of positive charges in the active site. A 180° rotation about the vertical axis shows that the rest of the enzyme surface is relatively less charged than the active site. |
![[Figure 1]](kw5089fig1.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
