Functional and structural roles of the N-terminal extension in Methanosarcina acetivorans protoglobin

► MaPgb*-ΔN20 shows an increased exposure of the haem propionates to the solvent. ► MaPgb*-ΔN20 displays the lack of a rate-limiting step in the azide binding process. ► MaPgb*-ΔN20 displays a marked biphasic behavior in the carbonylation process. ► MaPgb*-ΔN20Z shows a substantial loss of α-helical content. ► MaPgb*-ΔN20Z has very slow ligand binding rates, independent of ligand concentration.