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That green muck you see on a pond’s surface is one
step closer to becoming a solar-powered source of some of the stuff you use
every day. Scientists from the U.S. Department of Energy’s Lawrence Berkeley
National Laboratory (Berkeley Lab) and Stanford University have developed a way
to send molecules and proteins across the cell wall of algae, a feat that opens
the door for a new way to study and manipulate these tiny organisms.
In recent years, algae have become a hot prospect
as a way to synthesize biofuels, chemical building blocks, vaccines,
pharmaceuticals, and other useful compounds. The idea is to engineer algae to
secrete fuel for your car or other compounds using sunlight as an energy source
and carbon dioxide as a carbon source.
But before scientists learn the best ways to
harness the power of algae, they must first gain a better understanding of what
happens inside algae cells. They must also learn how to optimize the
inner-workings of algae for the production of biofuels and other applications.
This requires slipping molecular-sized cargo inside
algae cells to track metabolic changes and the flux of carbon, or to tweak the
cell’s energy-producing mechanisms. And this is where the going gets difficult.
Algae cells are protected by a double defense—an outer wall and lipid
membrane—that blocks unwanted molecules from getting inside.
Now, Berkeley Lab scientists have broken the algae
barrier. They’ve shown that a specially developed molecular transporter can
deliver small molecules, and larger molecules such as proteins, through the
cell wall and membrane of certain species of algae.
“We show for the first time that a guanidinium-rich
molecular transporter can deliver a variety of cargo in several algae species,”
says Bahram Parvin, a staff scientist in Berkeley Lab’s Life Sciences Division. “The range of uses for this molecular transporter is likely to be very broad.
It could offer insights on algae barriers and serve as a new tool for the
molecular manipulation and imaging of algae.”
The research was led by Berkeley Lab’s Joel Hyman
and Stanford University’s Erika Geihe and Brian Tantrow. Parvin and Stanford
University’s Paul Wender are the co-corresponding authors of the research,
which is described in the Proceedings of the National Academy of Sciences.
The scientists started with a molecular transporter
(also known as a cell-penetrating peptide or protein transduction domain) that
features arginine, one of the amino acids found in all proteins. Arginine is in
the guanidinium family of organic compounds. For the past several years,
Wender’s group has developed ways to deliver drugs and other small molecules
into mammalian cells using guanidinium-rich molecular transporters. They and
others have also laden transporters with cargo such as metals, imaging agents,
and genetic material.
But little was known about the ability of this type
of transporter to enter non-mammalian cells, especially those of organisms that
possess a cell wall.
The Berkeley Lab and Stanford University scientists
conducted several experiments that showed that guanidinium-rich molecular
transporters can cross the cell wall of an algae species called Chlamydomonas
reinhardtii, which was chosen because its molecular and genetic traits are
well understood. In one experiment, they fastened a protein cargo to the
transporter, and found that it too entered the cell. The scientists also showed
that the transporter can enter the cells of other algae species including Neochloris
oleoabundans and Scenedesmus dimorphus.
Until now, the main way researchers delivered
molecules inside algae cells was to use physical processes, such as shooting
tiny metal beads coated with DNA at cells. Another approach involves rapidly
shaking cells with small glass beads coated with DNA or small molecules. This
creates breaks in the cell wall and membrane, which allows the cargo to slip
inside. In contrast, the Berkeley Lab technique doesn’t require such
potentially damaging and inefficient methods.
The scientists next plan to refine the
guanidinium-rich molecular transporter so that it can be used to optimize the
energy-production pathways of algae. They’re modifying it so it can deliver genetic
cargo, and they’re developing it into a sensitive assay for imaging gene
expression. They’d also like to use it as a probe to track changes in algae’s
carbon cycle as a result of genetic engineering.
“With algae, we’ve lacked the kind of effective tools
for molecular and genetic engineering that we use in mammalian cells,” says
Parvin. “That’s changing now. Our technology could enable scientists to
manipulate algae’s energy-synthesis pathways and improve its ability to produce
biofuels, among other applications.”
