Title

Study of Zn(II) Binding of an Analog Methanobactin Peptide Using Ion Mobility-Mass Spectrometry

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Chemistry

Date of Award

Spring 2016

Abstract

Methanotropic bacteria are methane-oxidizing bacteria that produce copper chelating chromopeptides called methanobactins. Methanobactin produced by Methylosinus trichosporium [mb-OB3b] is currently best characterized and has been considered as archetype molecule. These modified chromopetides bind Cu(I) with high affinity and are hypothesized to mediate copper acquisition from the environment for the enzyme methane monooxygenase. A synthetic analog of methanobactin is synthesized to determine the effect of amino acid sequence changes on metal binding properties. The Zn(II) binding with analog methanobactin peptide with sequence acetyl-His1-Cys2-Gly3-Pro4-Tyr5-His6-Cys7 (amb5,Mw=857.96 Da) was analyzed as a function of pH and zinc ion concentration using ion mobility-mass spectrometry (IM-MS). Zn(II) was observed to form complex with amb5 peptide at pH > 6.0 , indicating the deprotonation of the imidazole N of His (pKa = 6.0) must occur to allow the initial anchoring of the Zn(II) ion. Although the Zn(II) complexes preferred forming an overall negative ion complex which is consistent with the two thiolate groups of Cys2 and Cys7 being involved in Zn(II) coordination. Collision induced dissociation experiments (CID) were conducted using IM-MS to determine the His, Cys binding sites of Zn(II). Collision cross-section measurements showed the Zn(II) negative ion complexes were smaller than the positive ion complexes, suggesting Zn(II) binds most compactly via the imidazole N of His and the thiolate groups of Cys. The lowest energy structures from the B3LYP/LanL2DZ level of theory showed the S of Cys2, carbonyl O of Cys2, S of Cys7, and O of the C-terminal was coordinated to Zn(II), producing an overall negative charged complex. The positive ion complexes of Zn(II) was shown to coordinate via the N of His1, carbonyl O of His1, ƐN of His6 and O of C-terminal in a distorted tetrahedral geometry.

Advisor

Laurence A. Angel

Subject Categories

Chemistry | Physical Sciences and Mathematics

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