Figure 4. CLD mutations in STAS domain exhibit loss of function.

Top: schematic diagram showing location of the chloride-losing diarrhoea (CLD) missense mutations I544N, and 2116delA which leads to termination at codon 711. Open bars indicate hydrophilic, putative cytoplasmic domains. The grey bar indicates the hydrophobic polytopic transmembrane domain. Hatch marks indicate that grey bar is shorter than if it was drawn to scale. Amino acid residue numbers under the bar mark approximate domain boundaries. Bottom: ³⁶Cl⁻ influx assay shows that both missense mutants exhibit loss of function; numbers of oocytes tested given in parentheses. Injected cRNA was 1 ng for wild-type (WT) hDRA and 10 ng for each mutant. Increasing cRNA to 50 ng did not lead to ³⁶Cl⁻ uptake by the mutants. Inset: hDRA immunoblot of whole oocyte lysates comparing WT hDRA with hDRA I544N polypeptide (10 ng injected cRNA for each). hDRA 2116delA, lacking the C-terminus, is undetectable by the anti-hDRA C-terminal peptide antibody.