Probing ligand-induced conformational changes of human CD38

Area of Science:

• Biochemistry
• Molecular Biology
• Immunology

Background:

• CD38 is a lymphoid surface antigen with NAD+ glycohydrolase activity.
• It plays roles in cyclic ADP-ribose metabolism and T- and B-cell signaling.
• Understanding CD38's molecular dynamics is crucial for its functional roles.

Purpose of the Study:

• To investigate the molecular dynamics of the CD38 protein.
• To explore the relationship between CD38's active site and its epitope.
• To understand how ligand binding affects CD38 conformation and activity.

Main Methods:

• Proteolytic degradation assays (trypsin, chymotrypsin).
• Assays with substrates (NAD+) and inhibitors.
• Reductive cleavage assays using dithiothreitol.
• Analysis of conformational changes upon ligand binding.

Main Results:

• Both enzymatic and epitopic sites of CD38 are sensitive to proteases and reducing agents.
• Substrates and inhibitors protect these sites from degradation.
• Ligand binding induces conformational changes, shielding active and epitopic sites.
• Irreversible inactivation of enzymatic activity occurred upon NAD+ and dithiothreitol incubation, preserving the epitope.

Conclusions:

• CD38 exhibits conformational plasticity influenced by ligand binding.
• Ligand binding induces protective conformational changes in CD38.
• Paracatalytic inactivation mechanism may explain loss of enzymatic activity.
• These findings impact understanding of CD38 structure, disulfide bridge accessibility, and signaling functions.