TY - JOUR
T1 - The two halves of CFTR form a dual-pore ion channel
AU - Yue, Hongwen
AU - Devidas, Sreenivas
AU - Guggino, William B.
PY - 2000/4/7
Y1 - 2000/4/7
N2 - The cystic fibrosis transmembrane conductance regulator (CFTR) exhibits two conductance states, 9 picosiemens (pS) and 3 pS. To investigate the origin of these two distinct conductance states, we measured the single- channel activity of three truncated forms of CFTR. These include: TNR, which contains the first transmembrane domain, the first nucleotide binding domain, and the R domain; RT2N2, which contains the R domain, the second transmembrane domain, and the second nucleotide-binding domain; and T2N2, which contains only the second transmembrane domain and the second nucleotide-binding domain. The results show that TNR exhibits only the large conductance of 9.2 pS, whereas RT2N2 and T2N2 exhibit only the small conductance (3.8-4.0 pS). Co-expression of TNR with T2N2 resulted in a mixed pattern of two conductance states, which is similar to that observed in wild- type CFTR. In further studies, a 'dual-R mutant,' R34W and R347P in the transmembrane segment 6 of the first half of CFTR, severely impaired the large conductance channel without affecting the small conductance channel. The ion selectivity and gating behavior of the two conductance channels are different regardless of whether they are measured in wild-type CFTR or in truncated CFTRs. The ion selectivity of the large conductance channel is Br- > Cl- > I-, whereas the ion selectivity of the small conductance channel is Br- = Cl- = I-. The open probability (P(o)) of the large conductance is about 4-fold higher than that of the small conductance. Transition from closed to open states of the small conductance is not dependent upon the open or closed states of the large conductance. The independent behaviors of the two conductances in CFTR strongly suggest that CFTR may have two distinct pores. Thus, like C1C0, CFTR is likely to be a double-barreled ion channel, with the first half of CFTR forming the large conductance and the second half forming the small conductance.
AB - The cystic fibrosis transmembrane conductance regulator (CFTR) exhibits two conductance states, 9 picosiemens (pS) and 3 pS. To investigate the origin of these two distinct conductance states, we measured the single- channel activity of three truncated forms of CFTR. These include: TNR, which contains the first transmembrane domain, the first nucleotide binding domain, and the R domain; RT2N2, which contains the R domain, the second transmembrane domain, and the second nucleotide-binding domain; and T2N2, which contains only the second transmembrane domain and the second nucleotide-binding domain. The results show that TNR exhibits only the large conductance of 9.2 pS, whereas RT2N2 and T2N2 exhibit only the small conductance (3.8-4.0 pS). Co-expression of TNR with T2N2 resulted in a mixed pattern of two conductance states, which is similar to that observed in wild- type CFTR. In further studies, a 'dual-R mutant,' R34W and R347P in the transmembrane segment 6 of the first half of CFTR, severely impaired the large conductance channel without affecting the small conductance channel. The ion selectivity and gating behavior of the two conductance channels are different regardless of whether they are measured in wild-type CFTR or in truncated CFTRs. The ion selectivity of the large conductance channel is Br- > Cl- > I-, whereas the ion selectivity of the small conductance channel is Br- = Cl- = I-. The open probability (P(o)) of the large conductance is about 4-fold higher than that of the small conductance. Transition from closed to open states of the small conductance is not dependent upon the open or closed states of the large conductance. The independent behaviors of the two conductances in CFTR strongly suggest that CFTR may have two distinct pores. Thus, like C1C0, CFTR is likely to be a double-barreled ion channel, with the first half of CFTR forming the large conductance and the second half forming the small conductance.
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U2 - 10.1074/jbc.275.14.10030
DO - 10.1074/jbc.275.14.10030
M3 - Article
C2 - 10744680
AN - SCOPUS:0034616134
SN - 0021-9258
VL - 275
SP - 10030
EP - 10034
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
IS - 14
ER -