Figure 2. Examples of structural differences between schistosome and other L-type Ca_v channel α1 subunits.

A. Charge change in the Domain I pore region. The Domain I pore region of L-type α1 subunits is shown. Note the shaded residues four spots C-terminal from the absolutely conserved glutamic acid (E) that forms part of the selectivity gate. In L-type channels from most phyla, this residue is a negatively-charged aspartic acid (D, green). However, in platyhelminths and molluscs, both of which are classed as lophotrochozoans, this residue is uncharged (red). This is interesting, because a non-charged residue at this position is characteristic of some non L-type channels (eg, Ca_v2.3). Accession numbers for sequences are: SmCa_v1A, AF361884; SmCa_v1B, Smp_159990; S. japonicum, Sjp_0099010; Fasciola (F. hepatica), Schmidtea (S. meditteranea), and Bdelloura (B. candida) are from DNA fragments we sequenced; Loligo (L. bleekeri), D86600; Lymnaea (L. stagnalis), AF484081; Cyanea (C. capillata), AAC63050; C. elegans, AAC47755; Drosophila, AAA81883; Ascidian (Halocynthia roretzi), BAA34927; Carp (Cyprinus carpio) Ca_v1.1, P22316; Rabbit (Oryctolagus cuniculus) Cav1.2, NM_001136522. B. SmCa_v1A contains one fewer positively charged residue in II-S4. Shown are residues in the fourth transmembrane region of domain II from SmCa_v1A and rat Ca_v1.2 (M67515). SmCa_v1A contains one fewer positively charged residue than Ca_v1.2. Positively charged arginines (R) and lysines (K) are highlighted in blue, and the substituted glutamine (Q) in SmCa_v1A is highlighted in red.