[GLOBULAR ACTIN IS THE PARTIALLY INTRINSICALLY DISORDERED PROTEIN WITH QUASI-STATIONARY STRUCTURE]

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Folding

Context:

• Globular actin (G-actin) exists as a quasi-stationary, thermodynamically unstable native state.
• This state is stabilized by divalent cations, typically Mg2+ in vitro and Ca2+ in vivo.
• Actin's native structure formation is an energy-dependent process involving chaperones like Hsp70, prefoldin, and the CCT complex.

Purpose:

• To investigate the thermodynamic stability of native globular actin (G-actin).
• To elucidate the mechanisms stabilizing G-actin's native conformation.
• To explore the implications of actin's quasi-stationary state for protein folding in general.

Summary:

• Native G-actin is thermodynamically unstable, requiring stabilization by Mg2+ (or Ca2+) and ATP.
• In vivo, complex post-translational folding processes involving chaperones (Hsp70, prefoldin, CCT) are essential for forming the native, stabilized actin structure.
• Denatured actin undergoes self-association into stable aggregates of 14-16 molecules, indicating that quasi-stationary native states may be common and require cellular assistance for formation.

Impact:

• Reveals the energetic cost and complex machinery required for achieving functional protein structures.
• Suggests that many proteins may exist in quasi-stationary states, necessitating cellular chaperones and cofactors.
• Provides insights into protein misfolding and aggregation, relevant to cellular function and disease.