Conformational changes in the fibronectin binding MSCRAMMs are induced by ligand binding

Area of Science:

• Microbiology
• Biophysics
• Structural Biology

Background:

• Bacterial adherence to host tissues is mediated by surface adhesins.
• Microbial surface components recognizing adhesive matrix molecules (MSCRAMMs) are a key subfamily of adhesins.
• MSCRAMMs bind extracellular matrix components, facilitating bacterial adhesion.

Purpose of the Study:

• To biophysically characterize recombinant fibronectin-binding MSCRAMMs from Gram-positive bacteria.
• To investigate the structural changes in MSCRAMMs upon binding to fibronectin.

Main Methods:

• Circular dichroism (CD) spectroscopy was used to analyze protein secondary structure.
• Far-UV CD spectra (190-250 nm) were measured for recombinant MSCRAMMs.
• Intrinsic viscosity measurements were performed to assess protein conformation.
• Tryptophan fluorescence spectroscopy was used to monitor ligand binding interactions.

Main Results:

• Recombinant MSCRAMMs exhibited minimal regular secondary structure in solution.
• The native and denatured conformations of the MSCRAMM ligand-binding domain were indistinguishable.
• Binding of the fibronectin NH2-terminus to MSCRAMMs induced a significant shift towards a beta-sheet conformation.
• Fibronectin binding induced a conformational change in the MSCRAMM, not in the fibronectin.

Conclusions:

• Fibronectin-binding MSCRAMMs undergo an induced conformational change upon ligand binding.
• This structural transition involves the formation of a predominantly beta-sheet secondary structure in the MSCRAMM.
• The findings provide insights into the molecular mechanisms of bacterial adherence to host tissues.