Fig 2.
Quaternary structure and active-site assembly in trans. (A) Superpositional docking of IntSSV protomers on Cre HJ DNA (Z score, 7.8). IntSSV subunits superpositioned on chains A and B of the Cre HJ complex are shown in blue and light blue, respectively, with the disulfide bond in yellow. Five of the six hallmark active-site residues are shown for chain A, while catalytic Tyr314 is instead depicted on chain B, along with the strictly conserved Lys243. Though not depicted, similar active-site constellations are found at the other subunit interfaces. Note that Tyr314 closely approaches the DNA arm bound by the adjacent subunit (dark blue) but is quite distant from the DNA arm bound by its own subunit (light blue). (B) The square circumscribing the active site in panel A is enlarged. The distribution of putative active-site residues across the subunit interface suggests that both Tyr314 and Lys243 are provided to the neighboring subunit in trans.