CARRIZO GARCIA Maria elena
Mechanisms of monomeric and dimeric glycogenin autoglucosylation
ISSOGLIO, FEDERICO M.; CARRIZO, MARÍA E.; ROMERO, JORGE M.; CURTINO, JUAN A.
JOURNAL OF BIOLOGICAL CHEMISTRY
AMER SOC BIOCHEMISTRY MOLECULAR BIOLOGY INC
Lugar: Baltimore; Año: 2012 vol. 287 p. 1955 - 1955
Initiation of glucose polymerization by glycogenin autoglucosylation at the Tyr194 residue is required to prime de novo biosynthesis of glycogen. It has been proposed that the synthesis of the primer proceeds by intersubunit glucosylation of dimeric glycogenin, even though it has not been demonstrated that this mechanism is responsible for the described polymerization extent of 12 glucoses produced by the dimer. We previously reported the intramonomer glucosylation capability of glycogenin without determining the extent of autoglucopolymerization. Here we describe that the maximum specific autoglucosylation extent (MSAE) produced by non-glucosylated glycogenin monomer is 13.3 ± 1.9 glucoses, similar to the 12.5 ± 1.4 glucose units measured for the dimer. The mechanism and capacity of the dimer enzyme to carry out full glucopolymerization was also evaluated by construction of heterodimers able to exclusively glucosylate by intrasubunit or intersubunit reaction mechanisms. The MSAE of non-glucosylated glycogenin produced by dimer intrasubunit glucosylation was 16% of that produced by the monomer. However, partially glucosylated glycogenin was able to almost complete its autoglucosylation by the dimer intrasubunit mechanism. The MSAE produced by heterodimer intersubunit glucosylation was 60% of that produced by the wild-type dimer. It is concluded that both intrasubunit and intersubunit reaction mechanisms are necessary for dimer enzyme to acquire maximum autoglucosylation. The full glucopolymerization capacity of monomeric glycogenin indicates that the enzyme is able to synthesize the glycogen primer without the need for prior dimerization.