β1-integrin folding requires both ERp57 and the calnexin cycle.
β1-integrin was translated in the presence of HT1080 SP cells stably
expressing V5-tagged ERp57 R282A and preincubated in the presence (lanes
2, 4, and 6) or absence (lanes 1, 3,
and 5) of castanospermine (CST). The control lane
(Con) shows β1-integrin translated for 120 min in the presence
of untransfected HT1080 SP cells. Lanes 1–6 were also analyzed
by densitometry, and the band intensity was plotted versus the gel
position for each time point.