Past exam of the biochemistry course of the University of Cambridge / 2025 / Paper 5 / Section 1 / 1 / c / Solution

The recovered vesicle fractions contain bands at the expected positions for the supplied SNARE proteins. The v-SNARE preparation contains its principal band, and the t-SNARE preparation contains both t-SNARE and the SNAP25 doublet. Thus protein-containing vesicle fractions have been recovered, consistent with successful reconstitution.

The SDS-PAGE experiment does not establish the orientation of the proteins, their proportion facing outward, the stoichiometry in an individual vesicle, or membrane fusion. Nor does a stained band prove that all of its protein is correctly folded and active. Those are separate functional and membrane topology questions.