Adenosyltransferase that catalyzes the conversion of cob(II)alamin to adenosylcob(III)alamin (AdoCbl) in the presence of ATP and an electron donor. Acts as an accessory protein of IcmF that functions in cofactor repair, since IcmF is prone to inactivation during catalytic turnover due to the occasional loss of the 5'-deoxyadenosine moiety and formation of the inactive cob(II)alamin cofactor in its active site. Thus, receives and repairs the inactive cofactor, which is then reloaded onto IcmF in a GTPase-gated step. AH2 + 2 ATP + 2 cob(II)alamin = A + 2 adenosylcob(III)alamin + 2 H(+) + 2 triphosphate Is potentially allosterically regulated by GTP/GDP, which enhances its affinity for AdoCbl by 5-fold. Binds cob(II)alamin weakly in the absence of ATP. The presence of ATP (but not GTP or GDP) increases the affinity of cob(II)alamin for the enzyme, and stoichiometric binding is observed. GTP blocks the transfer of cob(II)alamin to IcmF from ATR, thus averting its reconstitution with inactive cofactor. kcat is 3.8 min(-1). Homotrimer. Belongs to the Cob(I)alamin adenosyltransferase family.