Deciphering the interface between a CD40 receptor and borrelial ligand OspA

Area of Science:

• Microbiology
• Immunology
• Neuroscience

Background:

• Neuroborreliosis, a severe Lyme disease complication, involves Borrelia bacteria crossing the blood-brain barrier.
• Bacterial adhesion to brain microvascular endothelial cells (BMECs) is critical for neuroinvasion.

Purpose of the Study:

• To elucidate the molecular interface between Borrelia outer surface protein A (OspA) and the CD40 receptor involved in bacterial adhesion to BMECs.
• To identify specific amino acid residues mediating OspA-CD40 interactions.

Main Methods:

• Site-directed mutagenesis and binding assays were employed to analyze OspA-CD40 interactions.
• Truncation of OspA's human umbilical vein endothelial cell (HUVEC) binding domain was performed.
• Ligand-binding assays with OspA and CD40 fragments were utilized.

Main Results:

• A specific region (Asn127-Asp205) on OspA was identified as the CD40 binding site, containing a ligand-binding pocket.
• Disrupting this pocket abrogated CD40 binding.
• Specific OspA residues (Asp149, Phe165, Ala172, Val186, Leu192) and CD40's cysteine-rich domain 2 (CRD2) were implicated in the interaction.

Conclusions:

• The study precisely maps the OspA-CD40 interaction interface, revealing key residues and domains involved.
• Understanding these molecular interactions is vital for developing targeted therapeutics and vaccines against neuroborreliosis.