Posted on 04/20/2004 7:57:14 PM PDT by PatrickHenry
Red-blooded genealogists take note: The discovery in microbes of two oxygen-packing proteins, the earliest known ancestors to hemoglobin, brings scientists closer to identifying the earliest life forms to use oxygen.
According to the project’s lead investigator, University of Hawaii microbiologist Maqsudul Alam, the research may also aid in the search for blood substitutes as new molecular details shed light on how the structure of such proteins, called protoglobins, evolved to transport and release oxygen.
Scientists from the Maui High Performance Computing Center and the University of Texas Southwestern Medical Center contributed to the research. The findings will appear in the Proceedings of the National Academy of Sciences (PNAS) in an online “Early Edition” this week (at http://www.pnas.org) and in the April 27 print issue. A four-year, $500,000 grant from the National Science Foundation supported the project.
To life on primordial Earth, oxygen was poison. Within single-celled archaea, special proteins arose that captured and transported molecular oxygen, not to release it for respiration but to isolate and detoxify it to protect the organism. Archaea are a distinct group of microbes. Their lineage diverged long ago from a common ancestor they shared with bacteria and eukaryotes (plants, animals and other life forms that encase their DNA within a nucleus). Many strains of archaea exist, often in the planet’s harshest, hottest and oxygen-deprived environments. Some, however, adapted to use oxygen.
Alam’s research group found the two primitive protoglobulins in two different archaea species. One, Aeropyrum pernix, is limited to oxygen-based respiration, survives optimally in near-boiling saltwater, and was first discovered among thermal sea vents off Japan. The other, Methanosarcina acetivorans, uses several anaerobic – or oxygen-free – metabolic pathways that create methane gas. M. acetivorans is found in a wide range of realms, including lake-bottom muck, composting leaves, cow pies and human intestines. The genomes of both have recently been sequenced.
The ability to use oxygen for respiration allowed the diversity of life to expand vastly, an impact more fundamental, if perhaps not as dramatic, as the evolutionary transitions organisms made adapting from sea to land, from the ground to the air, or from “all fours” to upright.
Elizabeth Hood, who directs the areas of signal transduction and cellular regulation for NSF’s Division of Molecular and Cellular Biosciences, said, “As early life forms were established on earth, the atmosphere contained numerous toxic molecules, including nitric oxide and hydrogen sulfide. Early hemoglobins most likely evolved to bind and detoxify these gases. When oxygen became a component of the atmosphere, it was also toxic, and these early organisms used hemoglobin to bind and ultimately detoxify the oxygen.”
However, for advanced and larger life forms to exist in an oxygen-rich atmosphere on land, a mechanism was needed to take advantage of oxygen’s benefits, Hood said, and hemoglobins evolved into oxygen carriers rather than detoxifiers.
“Finding early hemoglobins in the most primitive life forms on earth testifies to their crucial role in the development of life as we know it today,” she said.
(In humans, with each breath in, hemoglobin binds oxygen in the lungs. Then, carried by blood cells made red by its oxygenated presence, the protein transports oxygen to tissues near and far in the body, where it then releases oxygen, which is essential to cellular respiration.)
To find the two protoglobins, the research team used advanced tools of biotechnology and high-performance computing, cloning genetic sequences from the two microbes and using specialized E. coli bacteria as gene-expression machinery to produce samples of the proteins. To analyze their structures, the team compared alignments with other members of the hemoglobin family of compounds. Computers generated models and created “molecular dynamic simulations” that illustrate with animations how the proteins bind with carbon monoxide, nitric oxide and oxygen.
Genetic sequences, binding characteristics and molecular structures of protoglobins were compared with those of hemoglobins and other oxygen-transport molecules from a wide range of organisms, including bacteria, tubeworms, roundworms, segmented “bloodworms,” mice, humans and sperm whales.
According to Alam, the similarities between these molecules and the protoglobins of A. pernix and M. acetivorans suggest “intriguing connections” between them and the evolution of mechanisms that sense oxygen, carbon monoxide, nitric oxide and hydrogen sulfide. These similarities, he said, also suggest connections to LUCA, short-hand for the “Last Universal Common Ancestor.”
“LUCA is believed to have been a metabolically ‘flexible’ single-celled organism with the ability to utilize oxygen for energy before free oxygen even existed in the air,” said Alam. “We think protoglobin helped give life to LUCA. And its descendents – hemoglobin, myoglobin, neuroglobin, and cytoglobin – allowed higher organisms to evolve” by allowing organisms to maintain a metabolic balance in an oxygenated world.
This article may point to yet another weakness in the "irreducable complexity" argument of Intelligent Design advocates.
So are liberals.
There's nothing in the bible that says Adam and Eve was God's first and only attempt at creation.
Their lineage diverged long ago from a common ancestor...
The ability to use oxygen for respiration allowed the diversity of life to expand vastly.
Early hemoglobins most likely evolved to bind and detoxify these gases...
... Hood said, and hemoglobins evolved into oxygen carriers rather than detoxifiers...
... “LUCA is believed to have been a metabolically ‘flexible’ single-celled organism with the ability to utilize oxygen for energy before free oxygen even existed in the air,...
Amazing amount of certainty in these statements. You have to admire someone with that much faith. I guess we are all just to smile and nod when such doctrines are stated.
I wonder if Evol-Doers have monasteries where the faithful can live simple lives and ponder the wonders of their faith to achieve this level of metaphysical certitude.
Instead of saying 'Thus saith the Lord', they just use an 'everybody knows Evolution happened, it is an insult to our intelligence to ask for details to back up our assumptions!' Pay no attention to the man behind the curtain.
So are liberals.
HAHAHAHA!
It's a real leap of faith to believe that in such a large universe (of which only 2.5% is ever going to be accessible, sensible or visible to us) that life wasn't developed/designed elsewhere, probably several times. No doubt it will even outlast the heat-death of the present physical universe in which we find ourselves ~ it's that well designed!
I agree. It's very annoying when people use imprecise language. It's like saying 'everybody knows' the earth is round, but did they run it by these people??
Thanks for bringing this to our attention, and don't let the creationists get you down.
Elizabeth Hood, who directs the areas of signal transduction and cellular regulation for NSF’s Division of Molecular and Cellular Biosciences, said, “As early life forms were established on earth, the atmosphere contained numerous toxic molecules, including nitric oxide and hydrogen sulfide. Early hemoglobins most likely evolved to bind and detoxify these gases. When oxygen became a component of the atmosphere, it was also toxic, and these early organisms used hemoglobin to bind and ultimately detoxify the oxygen.”
Hemoglobin is the Protein Data Bank's Molecule of the Month. (How could we have missed that???)
It mentions something interesting that I didn't know:
Use and Abuse of HemoglobinAside from oxygen transport, hemoglobin can bind and transport other molecules like nitric oxide and carbon monoxide. Nitric oxide affects the walls of blood vessels, causing them to relax. This in turn reduces the blood pressure. Recent studies have shown that nitric oxide can bind to specific cysteine residues in hemoglobin and also to the irons in the heme groups, as shown in PDB entry 1buw. Thus, hemoglobin contributes to the regulation of blood pressure by distributing nitric oxide through blood. Carbon monoxide, on the other hand, is a toxic gas. It readily replaces oxygen at the heme groups, as seen in PDB entry 2hco and many others, forming stable complexes that are difficult to remove. This abuse of the heme groups blocks normal oxygen binding and transport, suffocating the surrounding cells.
Is this what you're referring to?
Hemoglobin CousinsLooking through the PDB, you will find many different hemoglobin molecules. You can find Max Perutz's groundbreaking structure of horse hemoglobin in entry 2dhb, shown in the picture here. There are structures of human hemoglobins, both adult and fetal. You can also find unusual hemoglobins like leghemoglobin, which is found in legumes. It is thought to protect the oxygen-sensitive bacteria that fix nitrogen in leguminous plant roots. In the past few years some hemoglobin cousins called the "truncated hemoglobins" have been identified, such as the hemoglobin in PDB entry 1idr, which have several portions of the classic structure edited out. The only feature that is absolutely conserved in this subfamily of proteins is the histidine amino acid that binds to the heme iron.
And, if the article had used the words "might" or "maybe" you'd be lambasting the researchers for making up "just-so" stories.
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