Topology of mouse Panx1 based on hydrophobicity plots, site-specific antibodies, and glycosylation analysis (Locovei et al., 2006a; Boassa et al., 2007). (A) The topology of Panx1 in the membrane appears to be similar to that of connexins, with four predicted TM segments, two extracellular loops, and cytoplasmic localization of the amino and carboxy termini (Locovei et al., 2006a; Boassa et al., 2007; Penuela et al., 2007). Based on hydrophobicity analysis by the software programs TMpred, TMHMM, and DNA Star, the following boundaries for the TM segments are predicted: M38-I60 for TM1, F108-W127 for TM2, L217-236 for TM3, and L275-I296 for TM4. Because of uncertainty of the predictors, the boundaries in the figure are represented by a color gradient. Positions of endogenous cysteines are indicated with red numbers. The beginning (arrows) and end of stretches of amino acids substituted by cysteines for SCAM analysis are indicated by black numbers. (B) Localization of Panx1 SCAM mutants not forming functional channels. Clusters of these mutants are in the amino terminus, the first TM segment, and the third TM segment, indicating a structural importance of these moieties. (C) Positions of modified cysteines.