Nucleolar protein B23 has molecular chaperone activities

Area of Science:

• Molecular Biology
• Biochemistry
• Cell Biology

Background:

• Protein B23 is a nucleolar phosphoprotein involved in ribosome assembly.
• Previous studies suggested protein B23 possesses molecular chaperone-like activity.
• The precise chaperone functions of protein B23 required further investigation.

Purpose of the Study:

• To investigate the molecular chaperone activities of protein B23.
• To determine if protein B23 can prevent protein aggregation and maintain enzyme function.
• To explore the relationship between protein B23's chaperone activity and its role in ribosome biogenesis.

Main Methods:

• Assessed protein B23's ability to inhibit aggregation of HIV-1 Rev protein using light scattering.
• Tested protein B23's protective effects on liver alcohol dehydrogenase (LADH), carboxypeptidase A, citrate synthase, and rhodanese against thermal denaturation.
• Evaluated protein B23's capacity to restore activity to guanidine-HCl denatured LADH.
• Analyzed protein B23's binding properties to denatured proteins.

Main Results:

• Protein B23 significantly inhibited the aggregation of HIV-1 Rev protein in a concentration-dependent and saturable manner.
• Protein B23 protected LADH, carboxypeptidase A, citrate synthase, and rhodanese from thermal denaturation-induced aggregation.
• Protein B23 preserved LADH enzyme activity during thermal denaturation and restored activity to denatured LADH.
• Protein B23 preferentially bound to denatured substrates, interacting with exposed hydrophobic regions.

Conclusions:

• Protein B23 exhibits multiple molecular chaperone activities, including inhibition of aggregation and preservation/restoration of enzyme function.
• These demonstrated chaperone properties support a role for protein B23 in maintaining cellular protein homeostasis.
• The molecular chaperone functions of protein B23 are likely integral to its proposed role in ribosome biogenesis.