You know that a particular sequence at the C-terminus of the lectin ERGIC53 enhances its exit from the endoplasmic reticulum (ER). You create two mutant versions of the protein, one without the suspected sequence (1) and one in which the sequence is replaced with an ER retention signal (2). You transfect a fibroblast cell line with a plasmid that encodes either wild-type ERGIC53 (0) or one of the engineered versions of it (1 or 2). After inducing the expression of the proteins, you lyse the cells and either treat the lysate with endoglycosidase H (Endo H) or leave the lysate untreated, as indicated below. You then separate the proteins by SDS-PAGE and perform a Western blot to detect the bands corresponding to ERGIC53. Your results are represented in the following drawing. Which lanes (A to C) do you expect to correspond to each of the proteins 0, 1, and 2, respectively? Your answer would be a three-letter string composed of letters A to C only, e.g. CAB.

Question

Quizplus · Accepted Answer

Endo H-resistance is a sign that the protein has been transferred to the Golgi apparatus and has undergone processing. With wild-type protein (0, C), the protein shows partial Endo H-sensitivity. In the absence of the exit sign (1, A), transport to the Golgi is impaired, and most of the protein remains Endo H-sensitive. When an ER retention signal is also added (2, B), the protein seems to be completely Endo H-sensitive.

You Know That a Particular Sequence at the C-Terminus of the Lectin