Modeling study of human renal chloride channel (hCLC-5) mutations suggests a structural-functional relationship.
BACKGROUND
Dent's disease, a renal tubular disorder characterized by low-molecular-weight proteinuria, hypercalciuria, and nephrolithiasis, is due to inactivating mutations in the X-linked renal-specific chloride channel, hCLC-5. The x-ray crystal structures of two bacterial chloride channels (CLCs) have recently been established, thereby allowing us to construct a model for hCLC-5 and further examine the role of its mutations.


METHODS
The data regarding 49 hCLC-5 mutations were reviewed. Thirty-four mutations that predicted absent or truncated channels were excluded. The remaining 15 mutations (one in-frame insertion and 14 missense mutations), 12 of which have been studied electrophysiologically, were assessed. The hCLC-5 sequence was aligned with the Salmonella typhimurium and Escherichia coli sequences and used to map the hCLC-5 mutations onto a three-dimensional model.


RESULTS
hCLC-5 is a homodimeric protein, with each subunit consisting of 18 helices. None of the missense mutations involved the chloride (Cl-) selectivity filter, but 12 of the 15 mutations were found to be clustered at the interface of the two subunits. Six of these mutations occurred in two of the helices that either form part of the interface or lie in close proximity to the interface, and three other mutations that did not lead to complete loss of Cl- conductance were at the edge of the interface.


CONCLUSIONS
These results demonstrate a crucial role for the interaction between the two subunits at the interface of the homodimeric hCLC-5.
Wu
Fiona
F
Molecular Endocrinology Group, Nuffield Department of Clinical Medicine, University of Oxford, Botnar Research Centre, Nuffield Orthopaedic Centre, Headington, Oxford, United Kingdom.
Roche
Philippe
P
Christie
Paul T
PT
Loh
Nellie Y
NY
Reed
Anita A C
AA
Esnouf
Robert M
RM
Thakker
Rajesh V
RV
D000595:Amino Acid Sequence; D018118:Chloride Channels / Q000737:chemistry* / Q000235:genetics*; D018389:Codon, Nonsense; D019281:Dimerization; D006801:Humans; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship
C097503:CLC-5 chloride channel; D018118:Chloride Channels; D018389:Codon, Nonsense