Thermal-induced proteinquake in oxyhemoglobin

TL;DR

This study reveals a sudden mechanical transition in oxyhemoglobin crystals around 49°C, termed 'proteinquake', which may be relevant for understanding oxygen release mechanisms during temperature changes.

Contribution

It uncovers a temperature-induced mechanical transition in oxyhemoglobin crystals, distinct from denaturation, linked to its quaternary structure and potentially relevant for physiological oxygen release.

Findings

Oxyhemoglobin exhibits a sudden increase in Young's modulus at ~49°C.

Internal friction decreases sharply during the proteinquake.

The effect is specific to oxyhemoglobin's quaternary structure, not observed in myoglobin.

Abstract

Oxygen is released to living tissues via conformational changes of hemoglobin from R-state (oxyhemoglobin) to T-state (desoxyhemoglobin). The detailed mechanism of this process is not yet fully understood. We have carried out micromechanical experiments on oxyhemoglobin crystals to determine the behavior of the Young's modulus and the internal friction for temperatures between 20 C and 70 C. We have found that around 49 C oxyhemoglobin crystal samples undergo a sudden and strong increase of their Young's modulus, accompanied by a sudden decrease of the internal friction. This sudden mechanical change (proteinquake) takes place in a partially unfolded state and precedes the full denaturation transition at higher temperatures. The hemoglobin crystals after the proteinquake has the same mechanical properies as the initial state at room temperatures. We conjecture that it can be relevant for explaining the oxygen-releasing function of native oxyhemoglobin when the temperature is increased, e.g. due to active sport. The effect is specific for the quaternary structure of hemoglobin, and is absent for myoglobin with only one peptide sequence.