Characterization of Wiskott-Aldrich syndrome (WAS) mutants using Saccharomyces cerevisiae

Wiskott-Aldrich syndrome (WAS) is caused by alterations in the WAS protein (WASP), and 80% of the missense mutations are located in the WH1 domain, the region essential for interaction with the WASP-interacting protein (WIP). It has been suggested that loss of WASP-WIP interaction is causal to the disease. Las17p (yeast WASP) is essential for growth at 37 degrees C. The growth defect of the las17Delta strain can be suppressed by the expression of human WASP together with WIP. Using the las17Delta strain, we have analyzed 52 missense mutations in the gene encoding WASP and found that 13 of these mutant proteins were unable to suppress the growth defect of the las17Delta strain. The majority of these 13 mutations cause the classic WAS in humans and are located within the WH1 domain, while none of the 12 mutations outside the WH1 domain abolished the activity of WASP in Saccharomyces cerevisiae cells. This suggests that some of the mutations (13 out of 40) in the WH1 domain cause the syndrome in humans by perturbing the WASP-WIP complex formation, while the rest of the mutations cause the syndrome without affecting the WASP-WIP complex formation, but may affect the activity of the complex.