Solution NMR reveals micelle-stabilized α-helical segments flanking the RIPK1 RHIM amyloid core

Area of Science:

• Molecular biology
• Biochemistry
• Structural biology

Background:

• Receptor Interacting Protein Kinase 1 (RIPK1) is crucial in cell signaling pathways.
• RIPK1 can form amyloid assemblies via its RIP homotypic interaction motif (RHIM), influencing programmed cell death.
• Characterizing unassembled RIPK1 in solution is challenging due to its rapid aggregation.

Purpose of the Study:

• To characterize the solution-state structure of unassembled RIPK1.
• To investigate the structural basis of RIPK1's transition to amyloid assemblies.
• To compare RIPK1's structural behavior with RIPK3 under similar conditions.

Main Methods:

• Designed an aggregation-slowing mutant (N545D) of RIPK1.
• Utilized biophysical techniques to analyze RIPK1 structure under near-physiological pH.
• Employed SDS micelles to stabilize helical structures for wild-type RIPK1 analysis.

Main Results:

• Two segments within RIPK1's disordered domain exhibit nascent helical propensity.
• SDS micelles stabilize these helical structures, enabling characterization of wild-type RIPK1.
• RIPK3, despite a conserved RHIM, does not show comparable α-helical populations under analogous conditions.

Conclusions:

• RIPK1 possesses intrinsic helical propensity in its disordered regions, preceding amyloid formation.
• This helical propensity is specific to RIPK1 and not observed in RIPK3 under tested conditions.
• Understanding these structural dynamics provides insights into RIPK1-mediated cell signaling and amyloidogenesis.