Abstract
Transition Metals in Control of Microbial Physiology, Cancer
and Mammalian Development
All cells must acquire large numbers of transition metal
ions for use as essential cofactors in a multitude of
housekeeping enzymes; however, recent studies have shown that
dramatic time-dependent fluctuations in intracellular metal
availability control key biological events. In this session,
I will address recent insights into the inorganic chemistry
that cells use to get the right metal to the right place in the
cell. These discoveries are leading to new perspectives in
several fields including host-pathogen interactions, early
mammalian development and both normal and pathological
cellular proliferation processes.
The ensemble of metal concentrations is referred to as the
metallome of the cell. 1 As the nature of the metallome is
revealed for different types of cells, we are finding a general
pattern of metal ion utilization that is highly conserved
across evolution. These patterns of metal utilization are
perturbed in the earliest stage of mammalian developmental
states, in infectious disease and cancer cell proliferation.
A large number of specialized proteins are required to maintain
the intracellular quota for each essential metal within a
narrow range. While most metals are bound tightly in a variety
of well characterized metalloenzyme active sites, recent
studies of the emerging class of metal homeostasis proteins
reveal new types of biological coordination chemistry and are
inviting new questions about how specialized and aberrant cells
sense, acquire and deploy these metal ions. 2
Cells control their metallome, in part, via specific
metalloregulatory proteins, which sense changes in metal
availability and turn on or off specific genes. Studies of the
metalloregulatory proteins have revealed novel coordination
chemistry that gives rise to extreme thermodynamic sensitivity:
these proteins sense changes in zinc concentration in the
femtomolar range 1 or copper in the zeptomolar range 3 , and
then adjust the transcription of metal homeostasis genes in a
manner that keeps free metal ion concentrations in the cytosol
at vanishing low levels. Cells also control metal availability
through a family of proteins, which facilitate trafficking of
metals within the cell, namely metallochaperone proteins. 4
With this new protein-metal chemistry serving as a foundation
for understanding the inorganic chemistry of the cell, we are
now focusing on how host and pathogen battle for control over
fluctuations in metal availability. 5,6
Newly developed fluorescent metal-specific probes reveal
connections between subcellular distribution of metals and
proteins that insure appropriate sensing and trafficking.
While these small molecule probes are readily applied to
studies of live cells, there are a number of potential artifacts
and thus additional methods of interrogation are required.
Quantitative
single
cell
X-ray
fluorescence
microscopy
experiments at a variety of beamlines at the Advanced Photon
Source (Argonne National Laboratory) including the new
bionanoprobe, are rapidly emerging as some of the most powerful
tools to define these key developmental fluctuations in a
quantitative manner. We are using these approaches in
conjunction with other physical methods including confocal and
STEM microscopy to understand how zinc fluxes control
physiological decisions in the earliest stages of mammalian
development, including oocyte maturation, fertilization and
early embryonic development. 7,8 In parallel studies of the
malaria causing parasite, P. falciparum, we find that zinc
fluxes are essential in the blood stage of infectious cycle.
9 Thus metal fluxes involving movement of millions-to-billions
of metal ions between compartments of a single cell and the
extracellular environment are key regulatory events in both
infectious disease and mammalian development. Several cases
where changes in metal ion signatures play a central role in
physiology will be described with an emphasis on the role of
zinc as a master switch in the hours preceding and following
fertilization of the mammalian oocyte.
1. Outten, CE, O'Halloran, TV, "Femtomolar Sensitivity of
Metalloregulatory Proteins Controlling Zinc Homeostasis."
Science 2001, June 29; 292 (5526): 2488-92.
2. Davis, AV, O'Halloran, TV, "A Place for Thioether Chemistry
in Cellular Copper Ion Recognition and Trafficking." Nature
Chemical Biology , 2008, 4 , 148-151.
3. Changela, A. et al. "Molecular Basis of Selectivity and
Zeptomolar Sensitivity by CueR" Science , 2003, 301 ,
1383-1387.
4. Pufahl, RA, et al. "Metal Ion Chaperone Function of the
Soluble Cu(I) Receptor, Atx1" Science , 1997, 278 , 853-856.
5. Simm C, Luan CH, Weiss E, O’Halloran TV. High-throughput
screen for indentifying small molecules that target fungal zinc
homeostasis. PLoS One. 2011;6(9):e25136. PMC3182986
6. Raja MR, Waterman SR, Qui J, Bleher R, Williamson PR,
O’Halloran
TV.
“A
copper
hyperaccumulation
phenotype
correlates with pathogenesis in Cryptococcus neoformans,”
Metallomics. 2013 Mar 19. [Epub ahead of print] NIHMS457671
7. Kim, AM, et al. “Zinc Availability Regulates Exit From
Meiosis in Maturing Mammalian Oocytes.” Nat Chem Biol 2010
Sep,6(9);674-81.
8. Kim AM, Bernhardt ML, Kong BY, Ahn RW, Vogt S, Woodruff TK,
O’Halloran TV. Zinc sparks are triggered by fertilization and
facilitate cell cycle resumption in mammalian eggs. ACS Chem
Biol . 2011 Jul 15;6(7):716-23.
9. Marvin RG, Wolford JL, Kidd MJ, Ward J, Que EL. Mayer ML,
Penner-Hahn JE, Haldar K, O’Halloran TV. Fluxes in “free”
and
total
zinc
are
essential
for
progression
of
intraerythrocytic stages of Plasmodium falciparum. Chem Biol .
2012 Jun 22;19(6):731-41