Figure 4.

Structural elements determining the access to the active site of hCBS. A zoom-in view showing the structural elements delineating the entrance to the catalytic cavity in the SAM-free basal (grey) and in the SAM-bound activated (red) conformations of hCBSΔ516-525 in the absence of bound substrates. In the activated conformation, the loops L145–148, L171–174, and L191–202 adopt an open conformation that allows free access of substrates, whereas in the basal conformation these loops remain closed and compressed towards the catalytic center by structural elements from the regulatory domain of a complementary subunit (not shown for clarity). Reproduced by permission [195].