A mysterious space within a protein
critical to photosynthesis is filled with
fat molecules that influence both the
protein’s architecture and electrical
properties, according to two recent
Researchers studied the atomic
structure of, and electrical interactions
within, the cytochrome bf complex, a
protein complex central to the transport
of electrons within membranes of a plant
cell, a critical step in photosynthesis.
Photosynthesis is the process by
which plants, algae and bacteria convert
sunlight, carbon dioxide and water into
William Cramer, the Purdue professor who led the studies, says the step
in which electrons are transported in
the cytochrome complex is one of the
slowest steps in photosynthesis and is
of particular interest to those involved
in the effort to speed up the process.
“The ability to manipulate photosyn-
thesis — to make it faster or more effi-
cient — could improve some of the glob-
al issues we face,” says Cramer, the
Henry Koffler Distinguished Professor
of Biological Sciences. “It could lead to
crops that grow faster to help feed an
increasing population, and it could lead
to a source of clean energy. However,
before we can meaningfully manipulate
the proteins involved in photosynthesis,
we need to understand their structure
Cramer and S. Saif Hasan, a graduate
student whose doctoral thesis work laid
the foundation for this project, used
high-resolution X-ray crystallography
to reveal that a cavity within the protein
was filled with lipids, greasy molecules
commonly called fats. The team found a
total of 46 lipid-binding sites within the
influence key photosynthesis protein
protein, and the discovery could change
the way the biophysics-biochemistry
community thinks about membrane
proteins, Cramer says.
“It had been known that lipids created
a boundary around the outside of membrane proteins, but finding them inside
the protein could shift our thoughts on
how these complexes work,” he says.
“These lipids must be there for a reason,
and we are trying to determine exactly
what that is.”
The researchers suggest the lipids
help stabilize the structure of the pro-
tein, assist in the formation of super-
complexes that combine multiple pro-
tein complexes, and influence the ability
to move an electric charge bet ween dif-
ferent portions of the protein. A manu-
script detailing these findings was pub-
lished in the journal Structure.
Cramer, Hasan and Stanislav D.
Zakharov, a senior research associate in
Cramer’s laboratory, next collaborated
with Sergei Savikhin, an associate professor of physics, and graduate students Adrien Chauvet and Valentyn
Stadnystskyi to examine the electrical
interactions of the protein complex.
Through a new spectrophotometric
technique that simultaneously measures
both electron transfer within the cytochrome complex and strength of interactions that result from the transfer, the
team discovered that the electrical
interaction varied between the different
parts of the protein complex involved in
transporting electrons, called hemes.
The collaboration between biophysicists and physicists was essential to this
project, Cramer says. A paper detailing
the technique and findings was published
in the Journal of Physical Chemistry B.
A representation of the cytochrome
b6f complex and the interactions
between its four hemes is shown.
William Cramer, Purdue’s Henry
Koffler Distinguished Professor of
Biological Sciences, led studies that
found a space within the cytochrome
complex is filled with lipid molecules
that influence the protein’s architecture and electrical properties.