STRUCTURE, GLYCOSYLATION, AND LOCALIZATION OF RAT INTESTINAL GUANYLYL-CYCLASE-C - MODULATION BY FASTING

Guanylyl cyclase C (GC-C), an intestinal receptor guanylyl cyclase, bi nds diarrhea-producing bacterial Ligands such as the Escherichia coli heat stable enterotoxin. We examined the regulatory influence of feedi ng and fasting on the expression, structure, and biochemical propertie s of GC-C. When solubilized at 4 degrees C under nonreducing condition s, GC-C from both fed and fasted rats migrated on 7% sodium dodecyl su lfate-polyacrylamide electrophoretic gels as two extremely large aggre gates that barely penetrated the stacking and resolving gels. Chemical reduction of disulfide linkages disaggregated GC-C in fed but not fas ted rat samples, causing it to migrate as smaller forms (similar to 22 0 and 240 kDa). Although GC-C aggregates from fasted rats resisted thi s disaggregating effect of chemical reduction, they rapidly acquired i t within 90 min of refeeding. When solubilized at denaturing temperatu res (95 degrees C) under reducing conditions, GC-C aggregates largely disassembled into four smaller proteins (relative molecular weight sim ilar to 140,000, 131,000, 85,000, and 65,000). However, the 131-kDa gl ycoprotein was disproportionately increased in fasted rat membranes. T his unit and the 220-kDa unit were sensitive to endoglycosidase H. Sub cellular fractionation and immunohistochemical studies revealed a majo r redistribution of GC-C from surface to intracellular enterocyte site s during fasting.