Insight into the basis of glycogenin inactivation causing glycogenosis by mutational approach

CARRIZO, MARÍA E.; ROMERO, JORGE M.; ISSOGLIO, FEDERICO M.; CURTINO, JUAN A.

Potrero de los Funes, San Luis

Congreso; XLVII Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2011

Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB)

Glycogenin-1 is one of the two human glycogenin isoforms, mainly expressed in muscle. It displays 93% sequence identity with the rabbit enzyme, the best studied member of this protein family and the only one whose three dimensional structure has been solved. A missense mutation, Thr82Met, in one allele of the glycogenin-1 gene GYG1, producing human glycogenin inactivation and deficient priming of glycogen synthesis, was recently described. To analyze the structural basis of the loss of enzyme activity responsible for the human glycogenosis phenotype, we introduced the Thr82Met mutation into rabbit muscle glycogenin and solved its crystal structure. Thr82Met substitution resulted in only a few altered intramolecular residues interactions, while those with UDP-glucose were conserved. The results are consistent with the enzyme inactivation due to the prevented essential involvement of Asp162 in UDP-glucose activation, produced by loss of Thr82 to Asp162 hydrogen bonding, favored hydrophobic interactions between the replacing methionine and the neighboring amino acids, or both. Here we report the characterization of glycogenin mutants obtained by substitution of Thr82 with residues of different size and hydrophobicity, in an attempt to distinguish between the above proposed causes of inactivation.