Barrel Rigidity, Heme Distortion, Ligand Protection and Nitric Oxide Interactions with Heme in Nitrophorin 4

Persistent Link:
http://hdl.handle.net/10150/195615
Title:
Barrel Rigidity, Heme Distortion, Ligand Protection and Nitric Oxide Interactions with Heme in Nitrophorin 4
Author:
Amoia, Angela Michelle
Issue Date:
2006
Publisher:
The University of Arizona.
Rights:
Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Abstract:
Nitrophorins are nitric oxide transport proteins that aid in an insect obtaining a blood meal. The nitrophorins from the saliva of Rhodnius prolixus, a blood-sucking insect, consist of seven closely related proteins (rNP1-7). These proteins have the classic hallmarks that define the lipocalin protein family: an eight-stranded beta-barrel, binds a hydrophobic molecule, contains a flexible omega loop that lines the entrance to the binding cavity, contains a N-terminal helix and a conserved Trp-Arg/Lys interaction, and a disulfide bridge pattern. This dissertation explores the functional implications of the rNP4 structure. An apo structure of rNP4 to 1.11 angstrom resolution revealed the beta-barrel of rNP4 remains a rigid structure in the absence of its heme cofactor and is similar to that of holo rNP4. An X-ray crystallographic study of alterations to protein and heme cofactor was used to explore how heme distortion arises. In all altered proteins, local changes were seen at the point of alteration. The protein has evolved so as to have all surrounding contacts, as well as electronic interactions between ligand and heme, contribute to distortion. An omega loop triple alanine mutant of rNP4 that was unable to collapse over the binding cavity was used to investigate ligand (nitric oxide) protection crystallographically and kinetically. A 1.00 angstrom resolution structure confirmed the mutant protein was unable to collapse. The loop mutant, as well as wild-type protein, display NO binding to heme that was unaffected by oxygen, indicating that NO binds to heme before reacting with surrounding oxygen. NO-protein complex decay was very slow (hours) under conditions where NO was allowed to rebind to heme, highlighting the protection properties of rNP4. In the presence of oxygen and/or glutathione, which can react with NO, decay was accelerated but still slow (minutes to hours). Taken together, these data suggest that NO binds to the heme iron and then dissociates and associates hundreds of times before reacting with any surrounding compound.
Type:
text; Electronic Dissertation
Degree Name:
PhD
Degree Level:
doctoral
Degree Program:
Biochemistry & Molecular Biophysics; Graduate College
Degree Grantor:
University of Arizona
Advisor:
Montfort, William R
Committee Chair:
Montfort, William R

Full metadata record

DC FieldValue Language
dc.language.isoENen_US
dc.titleBarrel Rigidity, Heme Distortion, Ligand Protection and Nitric Oxide Interactions with Heme in Nitrophorin 4en_US
dc.creatorAmoia, Angela Michelleen_US
dc.contributor.authorAmoia, Angela Michelleen_US
dc.date.issued2006en_US
dc.publisherThe University of Arizona.en_US
dc.rightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.en_US
dc.description.abstractNitrophorins are nitric oxide transport proteins that aid in an insect obtaining a blood meal. The nitrophorins from the saliva of Rhodnius prolixus, a blood-sucking insect, consist of seven closely related proteins (rNP1-7). These proteins have the classic hallmarks that define the lipocalin protein family: an eight-stranded beta-barrel, binds a hydrophobic molecule, contains a flexible omega loop that lines the entrance to the binding cavity, contains a N-terminal helix and a conserved Trp-Arg/Lys interaction, and a disulfide bridge pattern. This dissertation explores the functional implications of the rNP4 structure. An apo structure of rNP4 to 1.11 angstrom resolution revealed the beta-barrel of rNP4 remains a rigid structure in the absence of its heme cofactor and is similar to that of holo rNP4. An X-ray crystallographic study of alterations to protein and heme cofactor was used to explore how heme distortion arises. In all altered proteins, local changes were seen at the point of alteration. The protein has evolved so as to have all surrounding contacts, as well as electronic interactions between ligand and heme, contribute to distortion. An omega loop triple alanine mutant of rNP4 that was unable to collapse over the binding cavity was used to investigate ligand (nitric oxide) protection crystallographically and kinetically. A 1.00 angstrom resolution structure confirmed the mutant protein was unable to collapse. The loop mutant, as well as wild-type protein, display NO binding to heme that was unaffected by oxygen, indicating that NO binds to heme before reacting with surrounding oxygen. NO-protein complex decay was very slow (hours) under conditions where NO was allowed to rebind to heme, highlighting the protection properties of rNP4. In the presence of oxygen and/or glutathione, which can react with NO, decay was accelerated but still slow (minutes to hours). Taken together, these data suggest that NO binds to the heme iron and then dissociates and associates hundreds of times before reacting with any surrounding compound.en_US
dc.typetexten_US
dc.typeElectronic Dissertationen_US
thesis.degree.namePhDen_US
thesis.degree.leveldoctoralen_US
thesis.degree.disciplineBiochemistry & Molecular Biophysicsen_US
thesis.degree.disciplineGraduate Collegeen_US
thesis.degree.grantorUniversity of Arizonaen_US
dc.contributor.advisorMontfort, William Ren_US
dc.contributor.chairMontfort, William Ren_US
dc.contributor.committeememberMcEvoy, Meganen_US
dc.contributor.committeememberCordes, Matthewen_US
dc.contributor.committeememberWalker, Annen_US
dc.contributor.committeememberHorton, Nancyen_US
dc.contributor.committeememberVierling, Elizabeten_US
dc.identifier.proquest1907en_US
dc.identifier.oclc659746473en_US
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