Assignment and secondary structure of calcium-bound human S100B

Area of Science:

• Biochemistry
• Structural Biology
• Protein NMR Spectroscopy

Background:

• Human S100B is a calcium-binding protein involved in various cellular processes.
• Understanding the structural dynamics of S100B upon calcium binding is crucial for elucidating its function.
• Previous studies on related proteins provide a basis for structural comparisons.

Purpose of the Study:

• To determine the complete NMR assignments of backbone resonances for calcium-bound human S100B.
• To identify the secondary structure of calcium-bound S100B using various NMR techniques.
• To investigate the structural changes in S100B upon calcium binding and compare it with other S100B variants.

Main Methods:

• Heteronuclear multidimensional NMR spectroscopy was employed for resonance assignments.
• Nuclear Overhauser Effect (NOE) correlations, amide exchange, coupling constants, and chemical shift index (CSI) analysis were used to identify secondary structure elements.
• Comparison of structural features with apo-rat and bovine S100B, as well as calbindin D9k.

Main Results:

• Complete backbone 1H, 13C, and 15N NMR assignments for calcium-bound human S100B were achieved.
• The secondary structure comprises four helices, three loops, and two antiparallel beta-strands forming a beta-sheet.
• Helix IV is longer in Ca-S100B compared to apo-rat and bovine S100B; significant chemical shift changes occur outside calcium-binding loops.

Conclusions:

• The secondary structure of calcium-bound human S100B has been elucidated.
• Calcium binding induces distinct structural alterations in S100B, including an extended Helix IV and changes in residues outside calcium-binding loops.
• These findings support the hypothesis that the C-terminus of Ca-S100B plays a role in protein-protein interactions.