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J. Biol. Chem., Vol. 283, Issue 14, 9414-9423, April 4, 2008

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Structure and Ligand Selection of Hemoglobin II from Lucina pectinata^*

José A. Gavira, Ana Camara-Artigas, Walleska De Jesús-Bonilla^¶, Juan López-Garriga^¶1, Ariel Lewis^¶, Ruth Pietri^¶, Syun-Ru Yeh^||, Carmen L. Cadilla^**, and Juan Manuel García-Ruiz

From the Laboratorio de Estudios Cristalográficos, CSIC, P.T. Ciencias de la Salud, 18100, Granada, Spain, the Department of Química-Física, Bioquímica y Química Inorgánica, Universidad de Almería, Carretera Sacramento, Almería, 04120, Spain, ^¶Chemistry Department, P. O. Box 9019, University of Puerto Rico, Mayagüez Campus, Mayagüez 00681, Puerto Rico, the ^||Department of Physiology and Biophysics, Albert Einstein College of Medicine, Bronx, New York 10461, and the ^**Biochemistry Department, Medical Sciences Campus, University of Puerto Rico, San Juan, Puerto Rico 00936

Lucina pectinata ctenidia harbor three heme proteins: sulfide-reactive hemoglobin I (HbI_Lp) and the oxygen transporting hemoglobins II and III (HbII_Lp and HbIII_Lp) that remain unaffected by the presence of H₂S. The mechanisms used by these three proteins for their function, including ligand control, remain unknown. The crystal structure of oxygen-bound HbII_Lp shows a dimeric oxyHbII_Lp where oxygen is tightly anchored to the heme through hydrogen bonds with Tyr³⁰(B10) and Gln⁶⁵(E7). The heme group is buried farther within HbII_Lp than in HbI_Lp. The proximal His⁹⁷(F8) is hydrogen bonded to a water molecule, which interacts electrostatically with a propionate group, resulting in a Fe-His vibration at 211 cm^-1. The combined effects of the HbII_Lp small heme pocket, the hydrogen bonding network, the His⁹⁷ trans-effect, and the orientation of the oxygen molecule confer stability to the oxy-HbII_Lp complex. Oxidation of HbI_Lp Phe(B10) Tyr and HbII_Lp only occurs when the pH is decreased from pH 7.5 to 5.0. Structural and resonance Raman spectroscopy studies suggest that HbII_Lp oxygen binding and transport to the host bacteria may be regulated by the dynamic displacements of the Gln⁶⁵(E7) and Tyr³⁰(B10) pair toward the heme to protect it from changes in the heme oxidation state from Fe^II to Fe^III.

Received for publication, June 19, 2007 , and in revised form, January 10, 2008.

The atomic coordinates and structure factors (code 2OLP) have been deposited in the Protein Data Bank, Research Collaboratory for structural Bioinformatics, Rutgers University, New Brunswick, NJ (http://www.rcsb.org/).

^* This work was supported by National Science Foundation Grant NSF-MCB-0544250 (to J. L. G.), National Institutes of Health NIGMS MBRS-SCORE 2 Grant S06GM08103-34 (to J. L. G.), Grants P20RR016470 and G12RR03051 from the National Center for Research Resources, National Institutes of Health, Grant BIO2006-15517-C02-02 from the Spanish Ministry of Education and Sciences, Project RMN-1344, the Junta de Andalucía (Spain) (J. A. G.), Factoría de Cristalización funded by the program Consolider-Ingenio 2010, and National Institutes of Health Grant HL65465 (to S. R. Y.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1 and S2.

¹ To whom correspondence should be addressed: P. O. Box 9019, University of Puerto Rico, Mayagüez Campus, Mayagüez, Puerto Rico 00681. Fax: 787-265-5476; E-mail: lopezj{at}uprm.edu.

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