PROTEOGLYCOGEN BIOSYNTHESIS: EVIDENCE FOR INACCESSIBILITY OF THE GLYCOGENIN-BOUND MALTOSACCHARIDE PRIMER TO FURTHER AUTOGLUCOSYLATION

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

Villa Carlos Paz, Córdoba, Argentina

Congreso; XLIV Reunión Anual de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2008

<!-- /* Font Definitions */ @font-face {font-family:"Cambria Math"; panose-1:2 4 5 3 5 4 6 3 2 4; mso-font-charset:0; mso-generic-font-family:roman; mso-font-pitch:variable; mso-font-signature:-1610611985 1107304683 0 0 159 0;} /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-unhide:no; mso-style-qformat:yes; mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Arial","sans-serif"; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-GB; mso-fareast-language:ES;} p.MsoBodyText, li.MsoBodyText, div.MsoBodyText {mso-style-unhide:no; mso-style-link:"Body Text Char"; margin:0cm; margin-bottom:.0001pt; text-align:justify; line-height:200%; mso-pagination:widow-orphan; tab-stops:0cm 36.0pt 72.0pt 108.0pt 144.0pt 180.0pt 216.0pt 252.0pt 288.0pt 324.0pt 360.0pt 396.0pt 432.0pt 468.0pt 504.0pt 540.0pt 576.0pt 612.0pt 648.0pt 684.0pt 720.0pt 756.0pt 792.0pt 828.0pt 864.0pt 900.0pt 936.0pt 972.0pt 1008.0pt 1044.0pt 1080.0pt 1116.0pt 1152.0pt 1188.0pt 1224.0pt 1260.0pt 1296.0pt 1332.0pt; font-size:12.0pt; mso-bidi-font-size:10.0pt; font-family:"Arial","sans-serif"; mso-fareast-font-family:"Times New Roman"; mso-bidi-font-family:"Times New Roman"; mso-ansi-language:EN-US; mso-fareast-language:ES;} span.BodyTextChar {mso-style-name:"Body Text Char"; mso-style-unhide:no; mso-style-locked:yes; mso-style-link:"Body Text"; mso-ansi-font-size:12.0pt; font-family:"Arial","sans-serif"; mso-ascii-font-family:Arial; mso-hansi-font-family:Arial; mso-ansi-language:EN-US; mso-fareast-language:ES;} .MsoChpDefault {mso-style-type:export-only; mso-default-props:yes; font-size:10.0pt; mso-ansi-font-size:10.0pt; mso-bidi-font-size:10.0pt;} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The intramolecular autoglucosylation of glycogenin initiates the de novo biosynthesis of proteoglycogen, with formation of the glycogenin-bound maltosaccharide primer required by glycogen synthase for subsequent glucose polymerization. The tyrosine-bound maltosaccharide, produced by incubation of glycogenin with UDP-glucose, reaches a maximum polymerization degree of 13 glucose units at cessation of the reaction. No exhaustion of the substrate donor occurred at the autoglucosylation end and the full autoglucosylated enzyme continued catalytically active for transglucosylation of the alternative substrate dodecyl-b-maltoside. Even the autoglucosylation cessation once glycogenin acquired the mature maltosaccharide moiety, glycogenin species ranging rM 47 to 200 kDa, isolated from purified proteoglycogen after controlled amylolytic digestion, as well as proteoglycogen, where able to autoglucosylate. It was described that the a-1,4-linked glucoses adopts a left-handed helical structure in maltoheptaose. Such a helical structure adopted by the mature glycogenin-bound maltosaccharide might leave the last incorporated glucose spatially far from the glucosylation site, a restriction which might be overcome by branched-bound a-1,4-glucans. Our work provides the first evidence to date for glycogenin intramolecular autoglucosylation ending by inaccessibility of the built maltosaccharide to the glucosylating site of the enzyme.