Figure 1. Efficient secretion of AAT and ATIII in HEK293 cells requires their N-glycans.

A) See text for explanation of the individual steps of the lectin chaperone substrate binding cycle. All cartoons are created with BioRender.com. B) Non-sequential folding of serpins. Efficient folding of serpins is accomplished by initial folding of the C-terminal region (green), resulting in a solvent exposed RCL (purple), before N-terminal region (orange) fully folds resulting in active folded protein ²⁸. C) Features and modifications of AAT and ATIII. AAT and ATIII contain N-terminal cleavable signal sequences (grey box). AAT contains three glycosylation sites (red) and one free Cys (yellow). ATIII contains four glycosylation sites and six Cys paired into three disulfides bonds. Both AAT and ATIII possess a gate region (green), five β-strands (blue) comprising the central β-sheet. D) Tertiary structures of AAT (PDB: 1ATU) and ATIII (PDB: 1E05) with glycans (red), disulfides (yellow), and features from C denoted. E) Cells were transfected with AAT or ATIII, radiolabeled for 30 min and chased for the indicated times. F) Quantification of secreted AAT and ATIII from D. Standard deviations are displayed for three independent biological replicates for all plots.