Conservation of folding pathways in evolutionarily distant globin sequences

To test the hypothesis that the folding pathways of evolutionarily related proteins with similar three-dimensional structures but widely different seq uences should be similar, the folding pathway of apoleghemoglobin has been characterized using stopped-flow circular dichroism, heteronuclear NMR puls e labeling techniques and mass spectrometry. The pathway of folding was fou nd to differ significantly from that of a protein of the same family, apomy oglobin, although both proteins appear to fold through helical burst phase intermediates. For leghemoglobin, the burst phase intermediate exhibits sta ble helical structure in the G and H helices, together with a small region in the center of the E helix. The A and B helices are not stabilized until later stages of the folding process. The structure of the burst phase foldi ng intermediate thus differs from that of apomyoglobin, in which stable hel ical structure is formed in the A, B, G and Fl helix regions.