Structural and biochemical insight into glycogenin inactivation by the glycogenosis-causing T82M mutation

The X-ray structure of rabbit glycogenin containing the T82M (T83M according to previous authors amino acid numbering [1]) mutation causing glycogenosis showed the loss of Thr82 hydrogen bond to Asp162, the residue involved in the activation step of the glucose transfer reaction mechanism. Autoglucosylation, maltoside transglucosylation and UDP-glucose hydrolyzing activities were abolished even though affinity and interactions with UDP-glucose and positioning of Tyr194 acceptor were conserved. Substitution of Thr82 for serine but not for valine restored the maximum extent of autoglucosylation as well as transglucosylation and UDP-glucose hydrolysis rate. Results provided evidence sustaining the essential role of the lost single hydrogen bond for UDP-glucose activation leading to glycogenin-bound glycogen primer synthesis.

► T82M mutation does not change contacts with UDPG and Tyr194 positioning.
► Autoglucosylation, DBM glucosylation and UDPG hydrolysis are abolished in T82M mutant.
► Glucose transfer activities are lost by Val but not by Ser substitution of Thr82.