H-1, N-15 AND C-13 NMR ASSIGNMENTS, SECONDARY STRUCTURE AND OVERALL TOPOLOGY OF THE ESCHERICHIA-COLI GLGS PROTEIN

GlgS is a 7892-Da protein which is involved in glycogen biosynthesis i n bacteria. We report the H-1, N-15 and C-13 NMR assignments of the ba ckbone and side-chain resonances at 25 degrees C and pH 6.7 from two-d imensional homonuclear and three-dimensional heteronuclear NMR experim ents. The secondary structure of the protein was determined using sequ ential and medium-range NOE correlations, vicinal (3)J(NH-H alpha) cou pling values and amide proton exchange rates. The secondary structure obtained is consistent with the secondary chemical shifts of H-1 alpha , C-13 alpha and C-13 = O. It was found that the secondary structure o f GlgS comprises two amphipathic helices (Asn10-Met21 and Glu39-Arg60) , one short highly hydrophobic helix (Ile30-Val33), a short extended b eta-strand-like fragment (Arg26-Asp29) and two type I beta-turns (His2 2-Gly25 and Thr34-Met37). An overall topology of GlgS is suggested bas ed on long-range NOEs. The elements of secondary structure form a sand wich in which the beta-strand and the short hydrophobic helix are posi tioned between the two amphipathic helices.