The modB mutation in the cellular slime mold Dictyostelium discoideum produces protein-linked glycans which appear to lack most of their original mass. In diploid strains homozygous for mutant alleles at this locus, it is also observed that 1) the putative contact sites A glycoprotein (gp80) is reduced to ca. 10% of its normal level, 2) reassociation of dissociated aggregation stage cells is markedly reduced, and 3) smaller fruiting bodies are formed. The expression of two other glycoproteins which normally bear the missing carbohydrate epitope do not appear to be affected at the level of resolution of immunofluorescence and SDS gel analysis. Based on these findings, we hypothesize that reduced gp80 expression on the cell surface results in reduced cell reassociation following dissociation and in reduced fruiting body size. We will investigate this hypothesis in the context of the larger question of glycan function in the accumulation and localization of developmentally-regulated glycoproteins. We will first investigate the basis for the decreased level of gp80, using synthesis and turnover studies and EM localization methods. We will then generate new mutations which alter the modB-dependent glycan, examine these modifications in terms of monosaccharide composition, glycan size distribution, and complementation analysis and then test for coordinate effects on gp80 expression, cell reassociation and fruiting body size (spore number). We speculate that by restoring a part of the missing glycan, or by removing only a part of it, by mutational means, we should be able to dissociate these effects of modB on gp80 accumulation and cell reassociation if they have a different structural basis. If we are unable to to dissociate the effects with even subtle changes in carbohydrate structure, we will infer that they are in fact due to a common mechanism (employing a common recognition process based on common structure) which prevents gp80 from arriving at the cell surface (or removes it once it arrives). Finally, glycan parameters for the other two glycoproteins carrying the carbohydrate epitope will be compared with these for gp80 to seek an explanation for the different effects of modB on their accumulation. We will compare the role of the modB-dependent glycan with another glycan, expressed on spore coat proteins, which carries an epitope recognized by another group of monoclonal antibodies. Using methods worked out for the modB-dependent glycan, we will investigate the role of this distinct glycan in distributing the spore coat proteins into prespore vesicles (whose exocytosis is developmentally regulated) and, following secretion, localizing the spore coat proteins into the spore coat, slime sheath and stalk tube.
| Gas-Pascual, Elisabet; Ichikawa, Hiroshi Travis; Sheikh, Mohammed Osman et al. (2018) CRISPR/Cas9 and glycomics tools for Toxoplasma glycobiology. J Biol Chem : |
| Xu, Xianzhong; Eletsky, Alexander; Sheikh, M Osman et al. (2018) Glycosylation Promotes the Random Coil to Helix Transition in a Region of a Protist Skp1 Associated with F-Box Binding. Biochemistry 57:511-515 |
| Sheikh, M Osman; Thieker, David; Chalmers, Gordon et al. (2017) O2 sensing-associated glycosylation exposes the F-box-combining site of the Dictyostelium Skp1 subunit in E3 ubiquitin ligases. J Biol Chem 292:18897-18915 |
| Sheikh, M Osman; Halmo, Stephanie M; Patel, Sneha et al. (2017) Rapid screening of sugar-nucleotide donor specificities of putative glycosyltransferases. Glycobiology 27:206-212 |
| Summers, Jody A; Harper, Angelica R; Feasley, Christa L et al. (2016) Identification of Apolipoprotein A-I as a Retinoic Acid-binding Protein in the Eye. J Biol Chem 291:18991-9005 |
| West, Christopher M; Blader, Ira J (2015) Oxygen sensing by protozoans: how they catch their breath. Curr Opin Microbiol 26:41-7 |
| Feasley, Christa L; van der Wel, Hanke; West, Christopher M (2015) Evolutionary diversity of social amoebae N-glycomes may support interspecific autonomy. Glycoconj J 32:345-59 |
| Sheikh, M Osman; Xu, Yuechi; van der Wel, Hanke et al. (2015) Glycosylation of Skp1 promotes formation of Skp1-cullin-1-F-box protein complexes in dictyostelium. Mol Cell Proteomics 14:66-80 |
| Chinoy, Zoeisha S; Schafer, Christopher M; West, Christopher M et al. (2015) Chemical Synthesis of a Glycopeptide Derived from Skp1 for Probing Protein Specific Glycosylation. Chemistry 21:11779-87 |
| Sheikh, M Osman; Schafer, Christopher M; Powell, John T et al. (2014) Glycosylation of Skp1 affects its conformation and promotes binding to a model f-box protein. Biochemistry 53:1657-69 |
Showing the most recent 10 out of 50 publications
