dictyNews Electronic Edition Volume 43, number 23 September 29, 2017 Please submit abstracts of your papers as soon as they have been accepted for publication by sending them to dicty@northwestern.edu or by using the form at http://dictybase.org/db/cgi-bin/dictyBase/abstract_submit. Back issues of dictyNews, the Dicty Reference database and other useful information is available at dictyBase - http://dictybase.org. Follow dictyBase on twitter: http://twitter.com/dictybase ========= Abstracts ========= O2 sensing–associated glycosylation exposes the F-box–combining site of the Dictyostelium Skp1 subunit in E3 ubiquitin ligases M. Osman Sheikh 1,2,3,6, David Thieker 2,6, Gordon Chalmers 2,4, Christopher M. Schafer 3, Mayumi Ishihara 2, Parastoo Azadi 2, Robert J. Woods 1,2, John N. Glushka 2, Brad Bendiak 5, James H. Prestegard 1,2, and Christopher M. West 1,3 1 Department of Biochemistry & Molecular Biology, University of Georgia, Athens, GA 30602 USA; 2 Complex Carbohydrate Research Center, University of Georgia, Athens, GA 30602 USA; 3 Dept. of Biochemistry & Molecular Biology, Oklahoma Center for Medical Glycobiology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104 USA; 4 Department of Computer Science, University of Georgia, Athens, GA 30602 USA; 5 Cell and Developmental Biology, University of Colorado Anschutz Medical Campus, School of Medicine, Aurora, Colorado 80045 USA 6 contributed equally J. Biol. Chem., in press Skp1 is a conserved protein linking cullin-1 to F-box proteins in SCF (Skp1- Cullin1-F-box) E3 ubiquitin ligases, which modify protein substrates with polyubiquitin chains that typically target them for 26S proteasome-mediated degradation. In Dictyostelium (a social amoeba), Toxoplasma gondii (the agent for human toxoplasmosis), and other protists, Skp1 is regulated by a unique pentasaccharide attached to hydroxylated Pro-143 within its C-terminal F-box– binding domain. Prolyl hydroxylation of Skp1 contributes to O2-dependent Dictyostelium development, but full glycosylation at that position is required for optimal O2 sensing. Previous studies have shown that the glycan promotes organization of the F-box–binding region in Skp1, and aids in Skp1’s association with F-box proteins. Here, nuclear magnetic resonance and mass spectrometry approaches were used to determine the glycan structure, and then a combination of NMR and molecular dynamics simulations were employed to characterize the impact of the glycan on the conformation and motions of the intrinsically flexible F-box–binding domain of Skp1. MD trajectories of glycosylated Skp1 whose calculated monosaccharide relaxation kinetics and rotational correlation times agreed with the NMR data indicated that the glycan interacts with the loop connecting two alpha-helices of the F-box–combining site. In these trajectories, the helices separated from one another to create a more accessible and dynamic F-box interface. These results offer an unprecedented view of how a glycan modification influences a disordered region of a full-length protein. The increased sampling of an open Skp1 conformation can explain how glycosylation enhances interactions with F-box proteins in cells. submitted by: Chris West [westcm@uga.edu] ============================================================== [End dictyNews, volume 43, number 23]