Fig. 1
Expression of two CACNA1A isoforms generated by alternative splicing of exon 24a in human nervous tissue. Upper panel A shows a schematic representation of the cassette exon 24a (left) and the amino acid sequences of the isoforms ΔSSTR and + SSTR (right), resulting from the alternative splicing event. The sequence shown corresponds to residues 1326 to 1358; the inclusion of the tetrapeptide (underlined red) occurs at the limit of the terminal portion of S3 and the extracellular loop connecting with S4 in domain III. Highlighted residues in yellow correspond to the S4 gating charges. The topology diagram of the hCav2.1 α1A subunit (middle) shows the location of the FHM-1 S218L mutation (blue diamond in the S4-S5 intracellular loop of domain I) and the tetrapeptide SSTR encoded by exon 24a (red circle domain III). Lower panel A: amino acid sequence of the S4-S5 linker of domain I (residues 191–237), with residue Ser218 labeled in blue, is shown below the topology diagram. Amino acid numbers correspond to the sequence of the clone used for generating the Cav2.1 cryo-EM structure (PDB: 8X90) used in our study for molecular modeling. B shows the comparison of copy number between transcript isoforms Δe24a and + e24a, obtained using qRT-PCR. Bar graphs represent the copy number values from different human tissue samples (see Table 1), derived from standard curves using qPCR CTs in triplicate. Error bars indicate the variability among replicates. The Δe24a variant is more abundant in the cerebellum and spinal cord, whereas + e24a is the predominant variant in the cerebral cortex