A homology model for the pore region of TRPV1 depicting the positions of the residues important for proton block (Glu636 and Asp646). Residue Glu636 is located on the pore helix, and Asp646 is immediately above the selectivity filter (TIGMG). Approximately one helical turn below Glu636 is another charged residue Lys639 (shown in blue). The model was constructed by homology modeling using the crystal structure of the KcsA channel as a template. See Ryu et al. (2007) for the alignment of sequences between the two channels.