Abstract/Details

Incorporation of histidine-rich metal -binding sites onto small protein scaffolds: Implications for imaging, therapeutics, and catalysis


2008 2008

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Abstract (summary)

Many histidine-rich sites in proteins bind transition metal ions such as Zn2+, natively. Such sites can encourage proper protein folding or allow access to enzymatic capabilities such as hydrolysis. Ru(II) and Tc(I) also bind to aromatic amines providing access to unique chemistries not observed in biology. Ru(II) complexes have shown efficacy in fighting cancer and catalysis, while 99mTc complexes are used in radio-imaging. To incorporate such metal-ions' activities into proteins, several mutants have been designed to bind Zn2+, Ru 2+, and Tc1+ by introducing three histidines onto their surfaces. The first design, Z0, utilized a chimeric approach by substituting a turn in engrailed homeodomain for the superimposable Zn 2+-binding loop of astacin. In the second design, 3HT-C, three histidine residues were incorporated into the N-terminus of the Trp-cage. The final scaffold, ubiquitin, was used to make two mutants: 3HIU with a 3-histidine containing loop inserted between residues 9 and 10, and 3HPU with 3-histidine point mutations near residues 35-38. Z0 proved unstable due to incorporation of a hydrophobic patch onto its surface and was not able to be isolated in sufficient quantities for study. However, the other proteins were stable and soluble. Zn2+-binding by 3HT-C was investigated by intrinsic tryptophan fluorescence quenching, circular dichroism, and RP-HPLC. Binding by 3HIU and 3HPU was studied by CD. All designed proteins bind to Zn 2+ with Kd values in the micromolar range. 3HIU and 3HPU were further studied for their ability to bind Ru(tacn)2+ complexes. While addition of Ru-complexes caused oligomerization to various extents depending upon reaction conditions, homogeneous Ru-protein monomers were purified by a combination of size-exclusion, cation-exchange and immobilized-metal affinity chromatographies. Ru-binding was confirmed by ESI-MS, and structural integrity was investigated by CD. Results indicate that Ru(tacn)2+ complexes can be bound to surface binding sites in proteins without disruption of structure, opening the door for the study of catalysis in a protein context. 99mTc(CO)3+-binding studies were performed with 3HIU by RP-HPLC. This protein binds Tc+ and resists substitution by free L-histidine, suggesting that peptidic Tc-binding tags could be designed with this approach to readily incorporate the radionuclide into any protein expression system.

Indexing (details)


Subject
Biochemistry;
Chemistry
Classification
0487: Biochemistry
0488: Chemistry
Identifier / keyword
Pure sciences; Histidine; Metal binding; Protein design; Protein engineering; Ruthenium protein; Technetium protein; Zinc protein
Title
Incorporation of histidine-rich metal -binding sites onto small protein scaffolds: Implications for imaging, therapeutics, and catalysis
Author
Soebbing, Samantha Lynn
Number of pages
158
Publication year
2008
Degree date
2008
School code
0096
Source
DAI-B 69/05, Dissertation Abstracts International
Place of publication
Ann Arbor
Country of publication
United States
ISBN
9780549582298
Advisor
Franklin, Sonya J.
Committee member
Kohen, Amnon; Margulis, Claudio; Rohde, Jan-Uwe; Tewson, Timothy
University/institution
The University of Iowa
Department
Chemistry
University location
United States -- Iowa
Degree
Ph.D.
Source type
Dissertations & Theses
Language
English
Document type
Dissertation/Thesis
Dissertation/thesis number
3310540
ProQuest document ID
219987861
Copyright
Database copyright ProQuest LLC; ProQuest does not claim copyright in the individual underlying works.
Document URL
http://search.proquest.com/docview/219987861
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