Probing inhibitors binding to human urokinase crystals by Raman microscopy: implications for compound screening.

Area of Science:

• Biochemistry
• Spectroscopy
• Drug Discovery

Background:

• Urokinase (enzyme) inhibition is a key strategy for antimetastatic cancer therapy.
• Raman spectroscopy offers potential for detailed molecular analysis of enzyme-inhibitor interactions.

Purpose of the Study:

• To investigate Raman spectroscopy's capability in characterizing inhibitor binding to human urokinase at a molecular level.
• To emphasize the utility of single-crystal studies for this analysis.

Main Methods:

• High-quality Raman spectra were obtained in situ from urokinase single crystals bound to five different inhibitors.
• Difference Raman spectroscopy was employed after inhibitor addition to isolate inhibitor-specific vibrational modes.
• Experimental and theoretical studies on naphthamidine compounds were used to identify amidinium moiety vibrational modes.

Main Results:

• Raman spectra revealed specific vibrational modes of the protonated amidinium group (around 1520 cm⁻¹) and naphthalene rings for bound inhibitors.
• The presence of the 1520 cm⁻¹ mode confirmed the protonated amidinium group within the urokinase active site for all five inhibitors.
• Single-crystal competitive binding experiments identified the inhibitor with the lowest inhibition constant (Kᵢ).

Conclusions:

• Raman spectroscopy is effective for in situ molecular analysis of enzyme-inhibitor complexes using single crystals.
• This technique provides advantages over solution-based studies, enabling competitive binding assays.
• Raman spectroscopy shows promise as a tool for drug design screening and as a complement to crystallographic analysis.