Structure and Function of Potential Glycosylation Sites of Dynactin-Associated Protein dynAP

Overexpression of human dynactin-associated protein (dynAP) transforms NIH3T3 cells. DynAP is a single-pass transmembrane protein with a carboxy-terminal region (amino acids 135–210) exposed to the outside of the cell possessing one potential N -glycosylation site (position 143) and a distal C-terminal region (residues 173–210) harboring a Thr/Ser-rich (T/S) cluster that may be O -glycosylated. In SDS–PAGE, dynAP migrates anomalously at ~ 45 kDa, much larger than expected (22.5 kDa) based on the amino acid composition. Using dynAP mutants, we herein showed that the T/S cluster region is responsible for the anomalous migration. The T/S cluster region is required for transport to the cytoplasmic membrane and cell transformation. We produced and purified the extracellular fragment (dynAP135–210) in secreted form and analyzed the attached glycans. Asn143 displayed complex-type glycosylation, suggesting that oligosaccharide transferase may recognize the NXT/S sequon in the secretory form, but not clearly in full-length dynAP. Core I-type O -glycosylation (Gal-GalNAc) was observed, but the mass spectrometry signal was weak, clearly indicating that further studies are needed to elucidate modifications in this region.