The heterotetradimers are fashioned pursuing the interaction of UPK2 and UPK3A moieties in the heterodimers. Following assembly within the endoplasmic reticulum plus the Golgi, six heterotetradimers organized in interior and outer rings68 form a 16?nm AUM particle or plaque (Fig. three), packaged into DFVs and delivered to the apical membrane69. T