Figure 1
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The topology of the CNG channel from retinal rod outer segment and its purification. (A) The sequences of the a- and b-subunits share a transmembrane topology with six membrane-spanning segments (S1-6), a pore between S5 and S6 and a cyclic nucleotide-binding domain (CNBD) at the C-terminus. The b-subunit alone has a glutamic acid rich protein (GARP) domain at the N-terminus and two calmodulin binding sites (CaM1 and CaM2) that are lacking in the a-subunit. (B) The proposed topology of the a- and b-subunits. Purified CNG channel was studied by (C) SDS PAGE and commassie staining and (D) Western blotting with antibodies against the a- and b-subunits. The a- and b-subunits run at apparent molecular masses of 63kDa and 240kDa respectively. The high content of glutamic acid residues in the GARP part of the b-subunit is suggested to be responsible for its anomalous migration on an SDS polyacrylamide gel (Körschen et al., 1995). |
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