For EndoH digestion, cell supernatants were concentrated by ultracentrifugation through a 20% (w/v) sucrose cushion (4 h at 100,000× g and 4 °C), and pellets were suspended in Tris-buffered saline TBS buffer (TBS; 50-mM Tris-HCl, pH 7.5, and 150-mM NaCl). Cells were lysed in TBS supplemented with 0.5% Nonidet P-40 (NP-40), and lysates were centrifuged for 5 min at 15,000× g and 4 °C. After the addition of 10 × glycoprotein denaturing buffer (New England Biolabs, Ipswich, MA, USA), samples were heated at 100 °C for 10 min. Next, samples were adjusted to 10 × GlycoBuffer 3 (New England Biolabs, Ipswich, MA, USA), divided in two portions and incubated for 1 h at 37 °C with or without 2-µL EndoH (New England Biolabs, Ipswich, MA, USA).