Biophys J, March 2000, p. 1227-1239, Vol. 78, No. 3

Coexpression of  and  Subunits of the Rod Cyclic GMP-Gated Channel Restores Native Sensitivity to Cyclic AMP: Role of D604/N1201

Laboratoire de Biophysique Moléculaire et Cellulaire (URA CNRS 520), DBMS, C.E.A.-Grenoble, Grenoble, France

Coexpression of the wt and wt subunits of the bovine rod channel restores two characteristics of the native channels: higher sensitivity to cAMP and potentiation of cGMP-induced currents by low cAMP concentrations. To test whether the increased sensitivity to cAMP is due to the uncharged nature of the asparagine residue (N1201) situated in place of aspartate D604 in the  subunit as previously suggested (Varnum et al., 1995, Neuron. 15:619-625), we compared currents from wild-type (wt and wt/wt) and from mutated channels (D604N, D604N/wt, and wt/N1201D). The results show that the sensitivity to cAMP and cAMP potentiation is partly but not entirely determined by the charge of residue 1201 in the  subunit. The D604N mutation in the  subunit and, to a lesser extent, coexpression of the wt subunit with the wt subunit reduce the open probability for cGMP compared to that of the wt channel. Interpretation of the data with the MWC allosteric model (model of Monod, Wyman, Changeux; Monod et al., 1965, J. Mol. Biol. 12:88-118) suggests that the D604N mutation in the  subunits and coassembly of  and  subunits alter the free energy of gating by cAMP more than that of cAMP binding.

Biophys J, March 2000, p. 1227-1239, Vol. 78, No. 3
© 2000 by the Biophysical Society   0006-3495/00/03/1227/13  $2.00

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