Elucidation and Control of Actinide Trafficking Pathways in Mammalian Cells

Chuan HeUniversity of Chicago

Department of Chemistry

Mark P. JensenArgonne National LabChemical Sciences and Engineering Division

Sixth Argonne – UChicago – Fermilab Collaboration Meeting, October 12, 2009

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The Nuclear Conundrum

Nuclear Energy is a carbon-free source for 20% of U.S. & world electricity production.

Why not 80%?

– Socio-economic reasons• Cost and economic risk• Proliferation of nuclear technology• Public worries about safety

– Technical reason• How do we handle the waste?

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Actinides? Really?

Recognizing metal ions with high selectivity and sensitivity is essential for life.Nature has evolved various metalloproteins to exploit and control metals.

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Objectives

Discover how cells handle toxic human-made metals, the transuranium actinides

1. Visualize actinide trafficking in cells with X-ray microbeams

2. Identify individual proteins that bind actinides in mammalian cells

3. Biochemically and structurally characterize actinide binding by various proteins

Create new ways to efficiently, economically, and safelyhandle actinides when they are no longer useful

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Where do Actinides Accumulate in Cells?

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First Structures of Pu-Containing Proteins

Small Angle X-Ray Scattering of Transferrins

One form of transferrin containingboth plutonium and iron has thesame shape as the native protein,which contains only iron.

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Blocking Pu Uptake by Cells Appears Possible

No Plutonium

“Bad” PlutoniumPuCFeNTf

“Bad” Plutoniumplus 50 uMchloroquine

Images of rat adrenal gland cellsAxes - coordinates in mm

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Could metal-binding proteins be redesigned to bind actinides?

NikR is a transcriptional repressor for expression of the nikABCDE operon in the presence of excessive concentrations of intracellular Ni+2

Ref: C. L. Drennan et al, Nat. Struc. Biol., 2003, 10, 794-799C. L. Drennan et al, PNAS, 2006, 103, 13676-13681

NikR

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MQRVTITLDD DLLETLDSLS QRRGYNNRSE AIRDILRSAL AQEATQQHGT QGFAVLSYVY EHEKRDLASR IVSTQHHHHD LSVATLHVHI NHDDCLEIAV LKGDMGDVQH FADDVIAQRG VRHGHLQCLP KED

Mutations:V72 → S V72SC95→ D, H, S V72S C95D H76→ D,E

V72S C95S H76→ D,E

NiN

S

N

NN

NHN

H

H

O NH

V72

3.7 A

4.4 AH76'

C95

H89

H87

UN

S

N

NN

NHN

H

H

O

O NH

V72S

H76'

C95

H89

H87

H

O

O

V72SU

N

NN

N

H

H

O

O NH

V72S

C95D

H89

H87

H

O

O

OO

OO

H76'D

H76D C95D

Design of an Actinyl Binding Site

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Design of an Actinyl Binding Site

The Kd of uranyl binding to NikR’was determined to be 53 nM

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Uranyl Binding and Function

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S. V. Wegner, H. Boyaci, H. Chen, M. P. Jensen, C. He, Angew. Chem. Int. Ed. (2009), 48, 2339.

Joint Publication

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Engineer bacteria to uptake, transport and store actinides

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Design Peptides that are Selective for Specific Actinides

LBT: DTNNDGWYEGDELLA1 53 9 12