Disorder with consequence: Phosphorylation sites in HSPB5 yield distinct structural outcomes

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Stress Response

Background:

• Small heat shock proteins (sHSPs) like HSPB5 are crucial for cellular stress response.
• Phosphorylation is a key mechanism regulating sHSP activity.
• HSPB5 has three phosphorylation sites in its N-terminal region (NTR) that influence its function.

Purpose of the Study:

• To investigate the impact of single and triple phospho-mimicry on HSPB5 oligomeric properties.
• To understand how different phosphorylation events on HSPB5 lead to distinct cellular outcomes.
• To elucidate the structural basis for altered chaperone activity in phosphorylated HSPB5.

Main Methods:

• Utilized phospho-mimicking mutations at serine residues (S19, S45, S59) in HSPB5.
• Assessed changes in oligomer size, subunit exchange, and hydrogen-deuterium protection patterns.
• Evaluated the effect of phosphorylation on HSPB5's ability to delay the aggregation of γD-crystallin.

Main Results:

• Single phosphorylation sites induced subtle changes in HSPB5 oligomerization and chaperone activity.
• Triple phospho-mimicry resulted in significant structural and functional alterations of HSPB5.
• The S45D phosphomimic demonstrated enhanced chaperone activity, with a structural rationale provided.

Conclusions:

• Distinct phosphorylation events on HSPB5 lead to differential structural and functional outcomes.
• Phosphorylation state critically modulates HSPB5's role as a cellular stress responder and chaperone.
• Findings provide structural insights into the mechanism of HSPB5 regulation by phosphorylation.