1. Andrew Yang
Health Careers High School
March 5, 2014

2. Introduction: Protein Structure
 Protein primary structure
arises from the protein’s
specific amino-acid
sequence.
 Amino acid sequence is
dictated by the central
dogma: DNA →
mRNA→ Codon →
Polypeptide (amino acid
sequence)

3. Relating Structure with Function
 Depending on the chemical
properties of the amino acids in
the primary structure, the
protein folds into a specific
secondary structure containing
α helixes and β pleated sheets.
 The protein’s actual 3-D
conformation is dictated by the
specific intermolecular
interactions between amino
acids in these α helixes and β
pleated sheets.
 Changes in tertiary structure
can alter protein function by
altering the amino acid
interactions and thus changing
the overall shape of the protein.

4. Mutations
 Genetic mutations occur when errors occur in DNA replication
or RNA transcription. These errors may change the amino acid
sequence and alter protein conformation at the location of the
mutation.
 Protein function may be compromised, as illustrated in this
figure below.

5. Human NADPH-Cytochrome P450 Reductase
• Human Cytochrome P450 Oxidoreductase (POR, shown
below), is an enzyme in the liver and other organs that transfers
electrons to the following cofactors, which are reduced as they
accept electrons:
NADPH →→ FAD →→ FMN →→ Heme (Fe)
•The heme group contains a central Iron atom which has high
affinity for electrons.

6. Functions of POR
 Various other Cytochrome
P450s found throughout the
body are dependent upon
POR’s electron transfer to
them.
 These Cytochrome P450s
are responsible for carrying
out important processes
such as drug metabolism
and steroid synthesis, as
shown in the figure to the
right.

7. POR Mutations: Antley-Bixler Syndrome
 Certain mutations of POR have been identified in
human patients and classified based on the amino
acid that has been altered.
 These patients seem to exhibit symptoms of AntleyBixler Syndrome, a rare genetic condition associated
with a loss of function in POR in which craniofacial
dysmorphism and/or altered steroidogenesis occurs
as a result (Miller, 2004).
Human Skull

8. POR Mutations: Location in POR
 The following figure shows the
locations of various mutations
that have been identified in POR.
 In this diagram, the FMN binding
domain is violet, the FAD binding
domain is blue, and the NADPHbinding domain is in green.
 A green dot indicates that the
mutation is “silent” and barely
impacts POR function, while a
red dot indicates that POR
activity is less than 25% of the
wild type POR activity. Note the
approximate location of the
highlighted S102P and R550Q
mutations whose structurefunction relationships are the
subject of this study.
S102P
R550Q

9. Impaired POR Function in Mutants
 Research in Dr. Masters’ Lab
indicates that binding affinity for
FAD, a cofactor in electron
transfer, is diminished in both the
V492E and R457H POR human
mutations. The human patients
with these defects have impaired
steroidogenesis and craniofacial
defects.
 In these two locations, the
mutation causes changes in
enzyme structure at the FAD
binding site, resulting in enzyme
instability and impairment of
POR activity compared with the
wild type protein as shown in this
electron density diagram.

10. S102P and R550Q Mutations
 The S102P (serine to proline
substitution) and R550Q (Arginine to
Glutamine) mutations were originally
found in human subjects from the
Czech Republic.
 It is unknown whether S102P and/or
R550Q impairs POR functionality,
since these subjects are anonymous
and, thus, any accompanying illness
is not known.
 For S102P, it is suspected that the
proline substitution will disrupt the
helical structure (creating a “kink”),
disrupting the conformation of the
protein in a crucial location in the
molecule.
S102P
R550Q

11. Objectives/Hypothesis
 Since many mutations in proteins can be
innocuous, we propose to characterize the S102P
and R550Q POR mutants for catalytic function as
well as structural aberrations, compared with wild
type POR. (Previously studied mutants were shown
to have lowered FAD or FMN binding affinities by
the Masters lab, suggesting that riboflavin therapy
could be efficacious.)
 It is expected that there will be a difference between
the electron transfer rates of the S102P, R550Q
mutants and the wild type POR when a cytochrome
c reduction assay is performed. These studies are
in progress.

12. Protein Expression
 In order to study the effects
of the mutation on the native
functionality of POR, a
fragment of human DNA,
which codes for POR, is
inserted into an E. coli
plasmid vector to transfer the
POR DNA into the bacteria to
be synthesized into protein.
 The E. coli cells are grown
with shaking in broth media in
3-liter flasks.
 The protein expressed by
these cells is purified and
collected for enzyme activity
analysis (e.g., Cytochrome c
reduction assay).

13. Transformation Experiments
•
Mutant POR is expressed by
the pET 28a vector E.coli
plasmid, which contains an
antibiotic resistance gene.
•
The vector is inserted into E.
coli BL-21 cells, and then the
cells are plated with agar,
which has the antibiotic
corresponding with the
antibiotic resistance gene in
the vector.
•
The resulting colonies appear
as white dots on the agar
plates and represent
individual cells.

14. Growth and Induction
•
The cells are bumped up to TB media at 37⁰C and grown in flasks for 24 hours on
a shaker.
•
Growth is monitored by measuring absorbance of the media with a
spectrophotometer.
•
When the cells are growing fastest at log phase with an absorbance of 0.6-0.8, a
chemical called IPTG is added; this process, called induction, allows the cells to
start expressing the protein of interest.

15. Experimental Plan

16. Harvesting
 After induction, the cells were spun down in the
centrifuge.
 The resulting pellet was collected and frozen.
 After thawing, the pellet was homogenized with lysate
buffer to release the protein from the cells and
centrifuged to rid the sample of cell debris, and the
supernatant was collected for purification

17. Protein Purification
 Nickel Affinity Chromatography is a method of
obtaining purer protein. The proteins are “tagged” by
adding additional histidine residues to the terminal
end. The Ni column captures the histidines
specifically and leaves untagged proteins behind.

18. Cytochrome c Reduction Assay
 This diagram shows the
electron transfer
mechanism occurring
between wild type POR
and its associated
Cytochrome P450 from
(NADPH → FAD → FMN →
Heme group).
 The Cytochrome c
reduction assay measures
electron transfer activity
of POR through the
absorbance changes in
Cytochrome c, which is
reduced and measured at
550 nm. Alternatively,
activity of the associated
Cytochrome P450 can be
measured.

19. Acknowledgements
I would like to thank:
 My mentors:
 Dr. Satya Panda and Dr. Bettie Sue Masters, as
well as Ms. Karen McCammon and Ms. Katie
Hinchee-Rodriguez for their guidance and
assistance in this project.
 My teacher:
 Ms. Catherine Gonzalez for teaching the
principles of scientific research.

20. References
 Hart S, Wang S, Nakamoto K, Wesselman C, Li Y, Zhong X
(2008). Genetic Polymorphisms in cytochrome P450
oxidoreductase influence microsomal P450-catalyzed drug
metabolism.
 Hart S, Zhong X (2008). P450 oxidoreductase: genetic
polymorphisms and implications for drug metabolism and
toxicitiy.
 Marohnic CC, Panda SP, Martasek P, Masters BS (2006).
Diminished FAD Binding in the Y459H and V492E AntleyBixler Syndrome Mutants of Human Cytochrome P450
Reductase. J Biol Chem 281: 35975-35982.
 Xia C, Panda SP, Marohnic CC, Martasek P, Masters BS,
Kim JP (2011). Structural basis for human NADPHcytochrome P450 oxidoreductase deficiency. Proceedings
of the National Academy of Sciences 108: 13486-13491.

21. Picture References
 http://www.docstoc.com/docs/22467824/NADPH-CytochromeP450-Oxidoreductase
 http://www.google.com/imgres?imgurl=&imgrefurl=http%3A%2F
%2Fwww.quora.com%2FHow-does-IPTG-induced-geneexpression-work-at-a-molecular-level
 http://www.uky.edu/Pharmacy/ps/porter/CPR.htm
 http://www.chempep.com/ChemPep-Generic-Term_Protein.htm
 http://www.addgene.org/plasmid_protocols/bacterial_transformati
on/
 http://www.bio-rad.com/en-us/product/protein-stains
 All other pictures and charts are either student-generated or used
with mentor permission