Congresos y reuniones científicas
Título:
Two molecular enzyme forms and reaction mechanisms for the glycogenin autoglucopolymerization
Autor/es:
ISSOGLIO, F.M.; CARRIZO, M.E.; ROMERO, J.M.; CURTINO, J.A.
Lugar:
Pto. Madryn, Chubut
Reunión:
Congreso; XLVI Reunión Anual-SAIB; 2010
Institución organizadora:
Sociedad Argentina de Investigacion Bioquimica y Biologia Molecular (SAIB)
Resumen:
The formation of glycogenin (Gn)-bound
á-1,4-oligoglucan primer is required for the de novo biosynthesis of
glycogen (G). Dimeric Gn, as it exists in solution and in the enzyme
crystals, was considered to be the molecular form which synthesizes the
primer by intersubunit glucosylation mechanism. We have described
however that monomeric Gn is also able to catalyze its intramolecular
glucopolymerization. In considering which Gn form actually primes G
biosynthesis, this might be determined by the polymerization degree (pd)
of the Tyr-linked oligoglucan the Gn form can produce, having the size
required by glycogen synthase and branching enzyme for further
elongation and branching. A pd of 12 was reported for the oligoglucan
produced by Gn dimer; however the auto-glucopolymerization extent
capacity of the monomer was unknown. Now we determined the
glucopolymerization degree of fully autoglucosylated monomeric and
homodimeric Gn and of heterodimers formed by mixing 1) a Gn mutant
lacking its tyrosine acceptor with a mutant containing the tyrosine
acceptor but lacking glucosylation activity, and 2) the wild type enzyme
with a mutant which lacked both, glucosylating activity and tyrosine
acceptor. The results show that besides the intersubunit glucosylation
of Gn dimer, the intramolecular glucosylation of Gn monomer can produce
the oligo-glucopolymer primer for G biosynthesis.