Regulation and dysregulation at a critical hematopoietic junction: The human WASP-WIP complex

Area of Science:

• Molecular biology
• Structural biology
• Immunology

Background:

• The Wiskott-Aldrich syndrome protein (WASP) and WASP-Interacting Protein (WIP) complex regulates cytoskeletal dynamics in hematopoietic cells.
• Mutations in WASP's N-terminal domain lead to primary immunodeficiencies: Wiskott-Aldrich syndrome (WAS) and X-linked thrombocytopenia (XLT).

Purpose of the Study:

• To determine the molecular structure of the WASP/WIP complex.
• To elucidate the mechanism of phosphoregulation and its impact on WASP ubiquitylation.
• To understand the structural basis of WAS and XLT.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy was used to determine the structure of the WASP/WIP complex.
• Analysis of phosphoregulation sites and mutation effects on the WASP/WIP interface.

Main Results:

• The study reveals an extensive binding interface where four WIP epitopes wrap around the EVH1 domain of WASP.
• Phosphoregulation occurs on two tyrosine residues, leading to the dissociation of the fourth WIP epitope (epi^IV) and exposing WASP ubiquitylation sites.
• Mild WAS-inducing mutations cluster at the WASP-epi^IV interface, suggesting a key molecular mechanism for the disease.

Conclusions:

• The determined structure provides a molecular context for WASP/WIP interactions in hematopoietic cells.
• This structural insight into WASP/WIP biology is crucial for understanding cytoskeletal regulation in health and disease.
• The findings are expected to aid in developing therapeutic strategies for WAS and XLT.