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Modulation of ligand–heme reactivity by binding pocket residues demonstrated in cytochrome c' over the femtosecond–second temporal range

Russell, Henry J and Hardman, Samantha JO and Heyes, Derren J and Hough, Michael A and Greetham, Gregory M and Towrie, Michael and Hay, Sam and Scrutton, Nigel S (2013) 'Modulation of ligand–heme reactivity by binding pocket residues demonstrated in cytochrome c' over the femtosecond–second temporal range.' The FEBS Journal, 280 (23). pp. 6070-6082. ISSN 1742-464X

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The ability of hemoproteins to discriminate between diatomic molecules, and the subsequent affinity for their chosen ligand, is fundamental to the existence of life. These processes are often controlled by precise structural arrangements in proteins, with heme pocket residues driving reactivity and specificity. One such protein is cytochrome c', which has the ability to bind nitric oxide (NO) and carbon monoxide (CO) on opposite faces of the heme, a property that is shared with soluble guanylate cycle. Like soluble guanylate cyclase, cytochrome c' also excludes O2 completely from the binding pocket. Previous studies have shown that the NO binding mechanism is regulated by a proximal arginine residue (R124) and a distal leucine residue (L16). Here, we have investigated the roles of these residues in maintaining the affinity for NO in the heme binding environment by using various time-resolved spectroscopy techniques that span the entire femtosecond-second temporal range in the UV-vis spectrum, and the femtosecond-nanosecond range by IR spectroscopy. Our findings indicate that the tightly regulated NO rebinding events following excitation in wild-type cytochrome c' are affected in the R124A variant. In the R124A variant, vibrational and electronic changes extend continuously across all time scales (from fs-s), in contrast to wild-type cytochrome c' and the L16A variant. Based on these findings, we propose a NO (re)binding mechanism for the R124A variant of cytochrome c' that is distinct from that in wild-type cytochrome c'. In the wider context, these findings emphasize the importance of heme pocket architecture in maintaining the reactivity of hemoproteins towards their chosen ligand, and demonstrate the power of spectroscopic probes spanning a wide temporal range. © 2013 FEBS.

Item Type: Article
Uncontrolled Keywords: cytochromec'; nitric oxide binding; protein dynamics; time-resolved infrared; transient absorption
Subjects: Q Science > QH Natural history > QH301 Biology
Divisions: Faculty of Science and Health
Faculty of Science and Health > Life Sciences, School of
SWORD Depositor: Elements
Depositing User: Elements
Date Deposited: 13 Jan 2014 15:15
Last Modified: 18 Aug 2022 11:05

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