Cleavage of disulfide bonds leads to inactivation and degradation of the type IIa, but not type IIb sodium phosphate cotransporter expressed in Xenopus laevis oocytes
G. Lambert et al., Cleavage of disulfide bonds leads to inactivation and degradation of the type IIa, but not type IIb sodium phosphate cotransporter expressed in Xenopus laevis oocytes, J MEMBR BIO, 176(2), 2000, pp. 143-149
Tris(2-carboxyethyl)phosphine (TCEP) reduces (cleaves) disulfide bonds of t
he renal proximal tubule type IIa Na/Pi- cotransporter (rat NaPi IIa) and t
hereby inhibits its function, We tested the effect of TCEP on the murine ty
pe IIa Na/P-i-cotransporter and the corresponding IIb intestinal isoform bo
th expressed in Xenopus laevis oocytes. After incubation with TCEP the func
tion of NaPi IIa was inhibited and protein amount was decreased, Injection
of the lysosomal inhibitor leupeptin prevented degradation of the protein.
Exposure of oocytes to TCEP at 0 degrees C led to a reduction in transport
function without concomitant loss in Na/Pi IIa protein. In contrast to NaPi
type IIa, the type IIb isoform was neither inhibited, nor degraded after i
ncubation with TCEP, These results suggest that cleavage of disulfide bonds
led to changes within the confirmation of the type IIa transporter that re
sult in (i) inhibition of the transport activity and (ii) internalization a
nd subsequent lysosomal degradation of transporter protein. Sequence compar
isons suggest the involvement/presence of different disulfide bonds in type
IIa and type IIb Na/P-i-cotransporters.