TABLE 2.
RetGC1 dimer (subunit A/subunit B) | Substrate in active site (subunit A/subunit B) |
---|---|
mOrangeRetGC1/mOrangeRetGC1a | GTP/GTPa |
GC1AC/GC1ACb | ATP/ATPb |
GC1AC rib(−)/GC1AC rib(−)c | Inactive/inactivec |
mOrangeM823R/mOrangeM823Ra | GTP/GTPa |
mOrangeR822P/mOrangeR822Pa | GTP/GTPa |
mOrangeM823R/GC1AC rib(−)d | Inactive/ATPd,e |
mOrangeR822P/GC1AC rib(−)d | Inactive/ATPd,e |
mOrangeM823R/GC1ACf | GTP/ATPf |
mOrangeRetGC1/GC1AC rib(−)d | Inactive/ATPd,e |
a Each subunit of RetGC1 in a dimer coordinates the purine base of GTP and provides coordination of ribose and Mg2+ for the second Mg2+GTP molecule in the active site (Fig. 10A) (28).
b RetGC1 with short ECD (37) was converted to adenylyl cyclase by the E925K/C997D substitutions as in Ref. 44.
c In addition to the E925K/C997D substitutions, the GC1AC also had the D929A mutation (24), disabling coordination of ribose and eliminating catalytic activity.
d The purine base of GTP is recognized by subunit A, but the opposite subunit B fails to coordinate ribose of the GTP, whereas ATP bound through the purine base by subunit B is held in a normal fashion by the Asp929 of subunit A (28).