2012 Summer Symposium Program - Middlebury College

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Wisath Sae-Lee (Momo) ‘13
Major: BIOCHEM
National Science Foundation
(Larrabee)
Jim Larrabee
William R. Kenan Jr. Professor
of Chemistry
Middlebury Summer Research Symposium 2012
separate magnetic minerals. The remaining non-magnetic fraction was run through
heavy liquid separation, using Methylene Iodide which has a density of 3.3 g/cm 3
to collect minerals that were higher in density—zircon has a density of ~4.6 g/cm 3 .
Pyrite also has a higher density, close to 5 g/cm 3 , and so some samples were reacted
in strong hydrofluoric acid baths to dissolve minerals other than zircons. Collected
zircons were then mounted in epoxy and polished for use in the scanning electron
microscope (SEM) and, later in the summer, the electron microprobe (EMP) at RPI
in Troy, NY for cathodoluminescence (CL) imaging. The laser ablation inductively
coupled plasma mass spectrometer (LA-ICP-MS) at RPI will be used to date a
random selection of ~80 detrital grains from each sample, by comparing the ratios
of uranium and lead isotopes to a standard. Geochemical and petrographic data for
each sample will be found using the ICAP spectrometer at Middlebury and by thin
section analysis. Further sampling and analysis farther north in the Craftsbury area
may provide insight into variability along the length of the formation.
Comparative MCD study of DapE-Encoded
N-Succinyl-l,l-Diaminopimelic Acid
Desuccinylase (DapE) from Haemophilus influenza
and Neisseria meningitides
Wisath Sae-Lee (Momo) and Jim Larrabee
Department of Chemistry and Biochemistry, Middlebury College, Middlebury VT 05753
DapE-Encoded N-Succinyl-l,l-Diaminopimelic Acid Desuccinylase (DapE) plays
an integral role in the biosynthesis of lysine (Lys) and meso-diaminopimelic acid
(mDAP). These biosynthetic processes provide essential components for both
protein synthesis and the construction of peptidoglycan in the bacterial cell wall.
Previous gene knock-out studies showed that the deletion of DapE gene induced
lethality even in lysine-supplemented media, suggesting that lysine cannot be
imported by other pathways. Since the lysine biosynthetic pathway is distinctive
to most gram-negative and some gram-positive bacteria, inhibitors of DapE could
provide selective bacterial toxicity. In this work, DapEs from Haemophilus influenza
(HiDapE) and Neisseria meningitides (NmDapE) were studied with various equivalents
of Co(II) with and without two different inhibitors—Caprtopril and Dithiothreitol
(DTT)—using magnetic circular dichroism (MCD). The result from the study of
the DapEs with Co(II) showed the electronic geometry of the two binding sites to
be 4- and 6-coordinate which have not been found in any other metalloenzymes.
The affinities of both sites in NmDapE appeared to be the same while the affinity of
the 4-coordinate site was higher than the 6-coordinate site for HiDapE. The MCD
spectra showed both inhibitors to be antiferromagnetically couple with the two
metals through a sulfide bridge.