[Model phospholipid membranes affect the holomyoglobin structure: conformational changes at pH 6.2].

Abstract

The influence of model negatively charged membranes on the sperm whale holomyoglobin structure at pH 6.2 has been investigated by different techniques (far and near UV circular dichroism, tryptophan fluorescence, absorbance at Soret band, differential scanning microcalorimetry and fast performance liquid chromatography). It is shown that the holomyoglobin structure undergoes a conformational transition from the native to intermediate state analogous to its apo-form. This state is characterized by the absence of a rigid tertiary structure and the native heme environment. At the same time, the content of alpha-helical secondary structure remains almost native. To change the holomyoglobin structure similarly to that of its apo-form in the presence of membranes, a higher molar phospholipids/protein ratio is required. The properties of holomyoglobin in the presence of negatively charged membranes resemble those of the molten globule state of its apo-form protein in aqueous solution. A possible functional role of the discovered non-native myoglobin state is discussed.