= Solution
\b[Partial proteolysis is one plausible explanation:] intact <SNAP25> and a slightly shortened form would migrate as two nearby bands in <SDS-PAGE>. Heterogeneous processing, a retained <affinity tag>, or an anomalously migrating species are other possibilities. The gel alone does not identify the chemical difference. Because the <proteins> were expressed in <Escherichia coli>, a mammalian <post-translational modification> should not simply be assumed. A <Western blot> establishing that both bands contain <SNAP25>, followed by <mass spectrometry>, could distinguish these explanations.
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