Analysis of lissencephaly-causing LIS1 mutations

Mutations in the LIS1 gene may result in severe abnormalities of brain cort ical layering known as lissencephaly. Most lissencephaly-causing LIS1 mutat ions are deletions that encompass the entire gene, therefore the mechanism of the disease is regarded as haploinsufficiency. So far, 13 different intr agenic mutations have been reported: one point mutation, H149R; deletion of exon 9, which results in deleted acids Delta 301-334; deletion of exon 4, which results in deleted amino acids Delta 40-64; 10 mutations resulting in truncated proteins and one predicted to result in extra amino acids. We st udied the consequences of the point mutation, deletion mutation and one of the reported truncations. In order to study LIS1 structure function: we int roduced an additional point mutation and other truncations in different reg ions of the protein. The consequences of these mutations to protein folding were studied by gel filtration, sucrose density gradient centrifugation an d measuring resistance to trypsin cleavage. On the basis of our results, we suggest that all truncation mutations and lissencephaly-causing point muta tions or internal deletion result in a reduction in the amount of correctly folded LIS1 protein.