Structural highlights
, pdb structure 3fhi[1], is shown with the catalytic unit's small lobe in gray and large lobe in tan, and the pka regulatory unit in light blue.
The . The residues from exon 1 of the catalytic unit are labelled by residue index. Note that the last three residues from exon 1 (residues # 13-15) are the only amino acids from the first exon of the catalytic unit that were included in this crystal structure. Also note the residues from the catalytic unit's downstream exons, which do in-fact interact with the regulatory unit - these interacting residues are represented with halos and ball-and-stick. As seen in the structure, the exon 1 residues are over 30 angstroms from the regulatory unit - too far to bind.
In support of the absence-of-interaction observation, in the crystal structure of the tetromeric holoenzyme, 3tnp[2], there is also no interaction between , shown with halos, to the regulatory units, shown in green and purple.
Moreover, the exon 1 residues are also - a second regulator/inhibitor of the catalytic unit.
This is also obvious from the pdb structure for the , 1atp[3].
