MIB2 and brain ischemia: To verify the importance of MIB2-mediated Lys-63-linked ubiquitination for lysosomal degradation, we tested its involvement in an experimental setting that mimics an important aspect of cerebral ischemia (sustained activation of glutamate receptors), which leads to a rapid down-regulation of GABAB receptors via lysosomal degradation (16, –, 19).