Wiskott-Aldrich Syndrome causing mutation, Pro373Ser restricts conformational changes essential for WASP activity in T-cells.

[wiskott-aldrich syndrome]

Wiskott-Aldrich Syndrome (WAS ) is caused by mutations in Wiskott-Aldrich Syndrome Protein (WASP ) and majority of the mutations are found in the WASP Homology 1 (WH 1 ) domain which mediates interaction with WIP (WASP Interacting Protein ), a WASP chaperone . Two point mutations together in the proline rich region (PRR ) domain of WASP (S 339 Y /P 373 S ) have been reported to cause WAS however the molecular defect has not been characterized . Expression of these mutants separately (WASPR (S 339 Y ), WASPR (P 373 S )) or together (WASPR (SP /YS )) did not rescue the chemotaxis defect or membrane projection defect of Jurkat (WKD ) T -cells (WASP knockdown ). This is not due to the inability of WASP-PRR mutants to form functional WASP-WIP complex in growth rescue experiments in las 17 Î” yeast strain . Expression of WASPR (S 339 Y ) but not WASPR (P 373 S ) or WASPR (SP /YS ) rescued the IL -2 expression defect of Jurkat (WKD ) T -cells , suggesting that Pro 373 S er mutation alone is sufficient to inhibit WASP functions in T -cell activation . The diffused localization of WASP-PRR mutants in activated Jurkat T -cells suggests that Ser 339 and Pro 373 are critical for WASP localization . WASP-PRR mutations either together or individually did not abolish interaction of WASP with sixteen WASP binding proteins including Hck , however they caused reduction in Hck mediated tyrosine phosphorylation of WASP which is critical for WASP activity . The auto-inhibitory conformation of WASP (P 373 S ) mutant was not relieved by the binding of Toca-1 or Nck 1 . Thus , our results suggest that Pro 373 S er mutation reduces Tyr 291 phosphorylation and prevents conformational changes required for WASP activity in chemotaxis and T -cell activation . Thus Pro 3373 Ser is probably responsible for all the defects associated with WAS in the patients .