Site-directed mutagenesis of bacterial hemoglobin: the role of glutamine (E7) in oxygen-binding in the distal heme pocket.

Dikshit, Kanak L and Orii, Y and Navani, N and Patel, Sangeeta and Huang, H Y and Stark, B C and Webster, Dale A (1998) Site-directed mutagenesis of bacterial hemoglobin: the role of glutamine (E7) in oxygen-binding in the distal heme pocket. Archives of biochemistry and biophysics, 349 (1). pp. 161-6. ISSN 0003-9861

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Abstract

The bacterial and yeast hemoglobins have a glutamine instead of histidine in the E7 position of the distal heme pocket. The recently determined crystal structure of Vitreoscilla hemoglobin (VHb) indicates that this residue is oriented out of the heme pocket and may not ligand the bound oxygen. This is in contrast to elephant myoglobin which also has a Gln(E7) but which does ligand the bound oxygen. This residue was changed in VHb using site-directed mutagenesis to leucine (VHbL) or to histidine (VHbH). Spectral and kinetic studies of the binding of oxygen and CO to VHbL showed that this substitution had little effect on the ligand-binding properties of this protein, evidence that Gln(E7) does not H-bond the bound ligand, in agreement with the findings of the crystallographic study of VHb. In contrast, the functional properties of VHbH were drastically altered in a way suggesting that the E7His may itself be liganded to the heme iron. These studies are further evidence that the distal heme pocket in VHb and related microbial hemoglobins differs from that in mammalian hemoglobins and may resemble in some ways the heme pocket in cytochrome b5.

Item Type:	Article
Additional Information:	Copyright of this article belongs to Elsevier Science
Subjects:	Q Science > QD Chemistry
Depositing User:	Dr. K.P.S.Sengar
Date Deposited:	02 Jan 2012 17:28
Last Modified:	09 Jan 2015 10:40
URI:	http://crdd.osdd.net/open/id/eprint/364

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