GS is the rate-limit ing enzyme for glycogen biosynthesis and its inactivalior contributes to the pathogenesis of type II diabetes. GS is regulated by multisite phosphorylation of the regulatory domains. Five phosphorylation sites are located in u proline-rich COOH-terminal regulatory domain (S640, S644, S648, S652 and S656). Sequential phosphorylation of these sites by CKII and GSK3 results in inactivation of GS. To understand the conformâtional basis of phosphorylation and inactivation of GS, 27-residue peptides containing these 5 phosphorylation sites were synthesized and the conformation of these peptides phosphorylated at different sites was determined by 1H NMR. When all 5 sites were phosphorylated, the 2D 1H NOESY spectra showed cross peaks that represent a close distance (-2.7 A) between the amide protons of A639-S640, S640-V641, L647-S648, S648-R649, S651-S652, Q653-S654, S654-E655. No cross peaks between P643-S644, S644-P645, and S652-P653 were observed due to lack of the amide proton in proline residues. The data indicated the existence of a β-turn conformation around the phosphorylated serine residues. When S640 was dephosphorylated, the cross peaks of A639-S640, S640-V64I disappeared, while other cross peaks were retained. On the other hand, when only S640 was phosphorylated, the cross peaks of A639-S640, S640-V641 wert detected, but no other cross peaks were observed. When all of 5 sites were dephosphorylated, NOE peaks for sequential amide-amide proton disappeared, indicating no β-tums around these serine residues. Together with previous studies, these results suggest that phosphorylation induces β-tum conformation around phosphorylation sites in the regulatory domain of GS, and these β-turn might be responsible for the inactivation of GS. The results also indicate that a β-turn conformation might be important for recognition by GSK3.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology