Differences in both glycosylation and binding properties between rat and mouse liver prolactin receptors

To investigate whether glycanic chains of prolactin receptors (PRL-R) play a role in hormone binding activity, comparison was made of rat and mouse liver solubilized receptors with respect to both their affinity for the hormone and their glycosylation properties. As compared with rat receptors, mouse receptors exhibited a 2-fold higher affinity for human growth hormone (hGH), the hormone being bound by both tissues with a lactogenic specificity. Along with this increased affinity, mouse receptors had a 2 lower M(r) relative to rat receptors (62 kDa versus 64 kDa as measured on hGH cross-linked receptors). These differences could be ascribed to different glycosylation properties of the receptors from the two species, as supported by the followings. 1) After treatment with endoglycosidase F (endo F), rat and mouse PRL-R no longer exhibited any difference in their M(r) (54 kDa for both cross-linked receptors). 2) Neuraminidase treatment increased by 37% the binding of hGH to mouse receptors, but was ineffective on the hormone-binding to rat receptors. Conversely, wheat germ agglutinin (WGA), another sialic acid specific probe, decreased hGH binding to rat receptors by 25%, but had no effect on this process for mouse ones. 3) Marked differences were observed in the recoveries of rat and mouse hormone-receptor (HR) complexes from ricin-1- (RCA1-), concanavalin A- (ConA-) and WGA-immobilized lectins. These differences were reduced (RCA1 and ConA) or abolished (WGA) after rat and mouse receptor desialylation by neuraminidase, a treatment which decreased the M(r) of both receptors by 2 kDa. Taken together, these results strongly suggest that the PRL-R from rat and mouse liver contain biantennary N-linked oligosaccharidic chains with distinct type of sialylation, which may account for their differential hormone-binding affinities.