High flow-resolution for mobility estimation in 2D-ENMR of proteins using maximum entropy method (MEM-ENMR)

Area of Science:

• Biophysical Chemistry
• Analytical Chemistry
• Spectroscopy

Background:

• Multidimensional electrophoretic NMR (nD-ENMR) offers potential for characterizing co-existing proteins and conformations.
• nD-ENMR utilizes electrophoretic migration rates in a new dimension to differentiate protein signals.
• Current limitations in nD-ENMR resolution stem from signal truncation due to electric field strength constraints.

Purpose of the Study:

• To introduce and validate the Burg's maximum entropy method (MEM) for analyzing truncated nD-ENMR signals (MEM-ENMR).
• To demonstrate the effectiveness of MEM-ENMR in enhancing electrophoretic flow resolution.
• To improve the structural characterization capabilities of nD-ENMR for protein mixtures.

Main Methods:

• Application of the Burg's maximum entropy method (MEM) to process truncated electrophoretic interferograms from nD-ENMR.
• Experimental validation using two-dimensional ENMR on lysozyme and a mixture of bovine serum albumin (BSA) and ubiquitin.
• Computer simulations to assess the removal of truncation artifacts and evaluate resolution enhancement.

Main Results:

• MEM-ENMR successfully analyzed truncated nD-ENMR signals, significantly enhancing flow resolution.
• Electrophoretic mobilities for lysozyme, BSA, and ubiquitin were accurately measured using MEM analysis.
• Simulations confirmed complete removal of truncation artifacts and demonstrated a 3- to 6-fold resolution improvement.

Conclusions:

• The Burg's maximum entropy method (MEM) is an effective signal processing technique for improving nD-ENMR resolution.
• MEM-ENMR overcomes limitations of signal truncation, enabling better differentiation of protein signals.
• This advancement enhances the utility of nD-ENMR for detailed structural characterization of complex protein solutions.