Honolulu, HA (07/15/04)- A primitive form of hemoglobin has been
found in single-cell microbes living in extreme environments, and is providing
an important clue about the way hemoglobin developed and changed over the
past 2.5 billion years.
Hemoglobin
is a molecule in blood that binds and transports oxygen in living creatures,
but whether it existed in early life forms on the planet was not known, until
now. The primitive hemoglobin structure, also called a protoglobin, is believed
to have been used in the ancient world to detect and bind oxygen, possibly
using the oxygen in the production of energy.
"It was very surprising to us that bacteria-like organisms which date
back 3.5 billion years would have a human-like hemo-globin protein," said
Maqsudul Alam, PhD, a microbiologist at the University of Hawaii, Honolulu.
Researchers began their path to the discovery of the protoglobin after they
came across an important clue. In the modern day Aeropyrum pernix,
of the archaea kingdom, they discovered the presence of a specific protein
known to be associated with hemoglobin.
A. pernix is an extremophile that lives in near-boiling water with
high salt concentrations. Researchers then studied another archaea organism, M.
acetivorans,
which is found in mud and identitied the same protein there.
The protein that they found had almost exactly the same structure as human
myoglobin, a molecule that stores oxygen in muscle tissue and has a structure
similar to hemoglobin. Humans have both hemoglobin and myoglobin.
"The question was, what was the origin of these proteins," said
Dr. Alam. Archaea are primitive organisms that tend to live in extreme environments,
these areas being similar to conditions on early earth. Going back billions
of years, "there was no oxygen, the atmosphere consisted mostly of gases
such as nitric oxide, carbon monoxide and hydrogren sulfide," he said.
Over the eons, small, isolated pockets similar to the harsh early environment
have persisted, as have some of the early archaea.
The archaea are believed to have changed very little over time, and it is
thought they are the progenitors of the other two kingdoms: the eukaryota
and bacteria.
For
the
Honolulu researchers, it made snese that, as in the other two kingdoms, the
archaea would have a form of hemoglobin in it, albeit a primitive form. And
that's exactly what they found.
"The protoglobins don't bind oxygen for transportation or storage very
well,"
Dr. Alam said. Indeed, the ability to bind and transport oxygen efficiently
to tissues that need it is a far more evolved and complex function than what
the protoglobins can do. By comparison the structure and function of the
protoglobins are quite simple.
Once the protein for the protoglobin was discovered, researchers took their
studies to another level and identified the genes for it. "We looked
initially for the proteins and then went back to the DNA. We localized the
gene," Dr.
Alam said.
Now that the genes have been sequenced for the protoglobin, the researchers
have applied for a patent and anticipate that the findings can be used in
the search for a novel blood substitute.
Knowing how a molecule such as hemoglobin is formed and the specific changes
it has undergone in its evolution is useful information when it comes to
genetic engineering. Potentially, the molecule can be altered in different
ways so it can be either a super-carrier of oxygen, or be used as an oxygen
detector. There could be several practical uses for the finding. "Once
you have the gene, you can modify that gene," Dr. Alam said. end
* Image is of model of protoglobin found in A. Pernix
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