Label-Free Single-Molecule Conalbumin Analysis

TL;DR

Researchers used nanoaperture optical tweezers to study conalbumin's behavior with and without iron, revealing temperature-dependent transitions and structural changes.

Contribution

The study demonstrates the use of nanoaperture optical tweezers to detect metal ion binding effects on conalbumin's conformational dynamics.

Findings

Iron-bound conalbumin showed higher corner frequencies in nanoaperture optical tweezers measurements.

Conalbumin in diluted egg white behaved like purified iron-free conalbumin.

Two-state transitions in conalbumin were temperature-dependent, with a dominant state at 30.4 °C.

Abstract

Nanoaperture optical tweezers (NOTs) were used to analyze conalbumin in various forms. By analyzing the power spectrum of the NOT-transmitted laser signal, differences between iron and iron-free conalbumin were observed; the corner frequency extrapolated to zero-laser power was significantly larger in magnitude for conalbumin with iron, which was interpreted as coming from the enhanced electrostatic interactions close to the surface of the nanoaperture. Conalbumin in a diluted, but otherwise unprocessed, egg white sample showed the same behavior as purified iron-free conalbumin. Dynamic two-state transitions in the NOT signal were observed for iron-free conalbumin and conalbumin in egg white samples. We used this to determine the dominant state as a function of temperature, with one state showing a maximum occupancy around 30.4 °C. Deconvolution of the probability distribution function was used to find the energy landscape associated with this two-state transition. This work shows the potential of NOTs to see variations with metal ion binding, including conformational dynamics related to the binding at timescales not accessible to other methods.

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