The CTA1 fragment catalyses ADP-ribosylation of the Gs alpha subunit (Gαs) proteins using NAD. The ADP-ribosylation causes the Gαs subunit to lose its catalytic activity of GTP hydrolysis into GDP + Pi, thus maintaining Gαs in its activated state.
The CTA1 fragment catalyzes the post-translational modification of Gαs proteins by ADP-ribosylation, leading to the loss of their ability to hydrolyze GTP, thus maintaining their active conformation.