The Root effect is a widespread property among fish hemoglobins whose structural basis remains largely obscure. Here we report a crystallographic and spectroscopic characterization of the non-Root-effect hemoglobin isolated from the Antarctic fish Trematomus newnesi in the deoxygenated form. The crystal structure unveils that the T state of this hemoglobin is stabilized by a strong H-bond between the side chains of Asp95α and Asp101β at the α(1)β(2) and α(2)β(1) interfaces. This unexpected finding undermines the accepted paradigm that correlates the presence of this unusual H-bond with the occurrence of the Root effect. Surprisingly, the T state is characterized by an atypical flexibility of two α chains within the tetramer. Indeed, regions such as the CDα corner and the EFα pocket, which are normally well ordered in the T state of tetrameric hemoglobins, display high B-factors and non-continuous electron densities. This flexibility also leads to unusual distances between the heme iron and the proximal and distal His residues. These observations are in line with Raman micro-spectroscopy studies carried out both in solution and in the crystal state. The findings here presented suggest that in fish hemoglobins the Root effect may be switched off through a significant destabilization of the T state regardless of the presence of the inter-aspartic H-bond. Similar mechanisms may also operate for other non-Root effect hemoglobins. The implications of the flexibility of the CDα corner for the mechanism of the T-R transition in tetrameric hemoglobins are also discussed.

An order-disorder transition plays a role in switching off the Root effect in fish hemoglobins / Vergara, Alessandro; Vitagliano, Luigi; Merlino, Antonello; Sica, Filomena; K., Marino; C., Verde; G., di Prisco; Mazzarella, Lelio. - In: THE JOURNAL OF BIOLOGICAL CHEMISTRY. - ISSN 0021-9258. - STAMPA. - 285:42(2010), pp. 32568-32575. [10.1074/jbc.M110.143537]

An order-disorder transition plays a role in switching off the Root effect in fish hemoglobins

VERGARA, ALESSANDRO;VITAGLIANO, LUIGI;MERLINO, ANTONELLO;SICA, FILOMENA;MAZZARELLA, LELIO
2010

Abstract

The Root effect is a widespread property among fish hemoglobins whose structural basis remains largely obscure. Here we report a crystallographic and spectroscopic characterization of the non-Root-effect hemoglobin isolated from the Antarctic fish Trematomus newnesi in the deoxygenated form. The crystal structure unveils that the T state of this hemoglobin is stabilized by a strong H-bond between the side chains of Asp95α and Asp101β at the α(1)β(2) and α(2)β(1) interfaces. This unexpected finding undermines the accepted paradigm that correlates the presence of this unusual H-bond with the occurrence of the Root effect. Surprisingly, the T state is characterized by an atypical flexibility of two α chains within the tetramer. Indeed, regions such as the CDα corner and the EFα pocket, which are normally well ordered in the T state of tetrameric hemoglobins, display high B-factors and non-continuous electron densities. This flexibility also leads to unusual distances between the heme iron and the proximal and distal His residues. These observations are in line with Raman micro-spectroscopy studies carried out both in solution and in the crystal state. The findings here presented suggest that in fish hemoglobins the Root effect may be switched off through a significant destabilization of the T state regardless of the presence of the inter-aspartic H-bond. Similar mechanisms may also operate for other non-Root effect hemoglobins. The implications of the flexibility of the CDα corner for the mechanism of the T-R transition in tetrameric hemoglobins are also discussed.
2010
An order-disorder transition plays a role in switching off the Root effect in fish hemoglobins / Vergara, Alessandro; Vitagliano, Luigi; Merlino, Antonello; Sica, Filomena; K., Marino; C., Verde; G., di Prisco; Mazzarella, Lelio. - In: THE JOURNAL OF BIOLOGICAL CHEMISTRY. - ISSN 0021-9258. - STAMPA. - 285:42(2010), pp. 32568-32575. [10.1074/jbc.M110.143537]
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11588/371043
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