Monomeric human soluble CD4 dimerizes at physiological temperature: VTSAXS data based modeling and screening of...

Area of Science:

• Biophysics
• Structural Biology
• Molecular Interactions

Background:

• Soluble CD4 (sCD4) was previously observed as a monomer in solution, with a shape resembling monomers in crystal dimers.
• The role of crystal packing effects in forming the dimeric state of CD4 remained unclear.

Purpose of the Study:

• To investigate the heat-induced association of soluble CD4 (sCD4) in solution.
• To determine if CD4 can form dimers independent of crystal packing effects.
• To identify potential small molecules that can disrupt CD4 dimerization.

Main Methods:

• Variable temperature small-angle X-ray scattering (VTSAXS) to study sCD4 association with temperature changes.
• Computational modeling using SAXS profiles and crystal structures to solve models of CD4 dimers.
• In silico screening of small molecules for binding to the D4 and D1 domains of CD4.
• VTSAXS experiments with sCD4 and screened molecules to assess disruption of dimerization.

Main Results:

• sCD4 dimerization was observed to increase with temperature, forming dimers around 35-40°C.
• The observed dimerization was partially reversible.
• Models of CD4 dimers showed D4-D4 interactions, suggesting pre-existing crystal-like associations in solution.
• Small molecules targeting the D1 domain, unexpectedly, could also inhibit dimerization, indicating a communication network within sCD4.

Conclusions:

• CD4 dimerization in solution is temperature-dependent and occurs independently of crystal packing.
• A communication network exists across the sCD4 structure, influencing self-association and molecule binding.
• The findings can inform the development of novel CD4-reactive immunosuppressive agents.