Search This Blog

Monday 19 June 2017

Actually,it is rocket science.

Rocket Science in a Microbe Saves the Planet
Evolution News & Views

Anammox. It's a good term to learn. Wikipedia's first paragraph stresses its importance:

Anammox, an abbreviation for ANaerobic AMMonium OXidation, is a globally important microbial process of the nitrogen cycle. The bacteria mediating this process were identified in 1999, and at the time were a great surprise for the scientific community. It takes place in many natural environments... [Emphasis added.]

And now, the news. A team of European scientists found something very interesting about the bacteria. Publishing in Nature, the researchers tell how they have ascertained the structure of a molecular machine that performs chemical wizardry using rocket science.

Anaerobic ammonium oxidation (anammox) has a major role in the Earth's nitrogen cycle and is used in energy-efficient wastewater treatment. This bacterial process combines nitrite and ammonium to form dinitrogen (N2) gas, and has been estimated to synthesize up to 50% of the dinitrogen gas emitted into our atmosphere from the oceans. Strikingly, the anammox process relies on the highly unusual, extremely reactive intermediate hydrazine, a compound also used as a rocket fuel because of its high reducing power. So far, the enzymatic mechanism by which hydrazine is synthesized is unknown. Here we report the 2.7 Å resolution crystal structure, as well as biophysical and spectroscopic studies, of a hydrazine synthase multiprotein complex isolated from the anammox organism Kuenenia stuttgartiensis. The structure shows an elongated dimer of heterotrimers, each of which has two unique c-type haem-containing active sites, as well as an interaction point for a redox partner. Furthermore, a system of tunnels connects these active sites. The crystal structure implies a two-step mechanism for hydrazine synthesis: a three-electron reduction of nitric oxide to hydroxylamine at the active site of the γ-subunit and its subsequent condensation with ammonia, yielding hydrazine in the active centre of the α-subunit. Our results provide the first, to our knowledge, detailed structural insight into the mechanism of biological hydrazine synthesis, which is of major significance for our understanding of the conversion of nitrogenous compounds in nature.

Dinitrogen gas (N2) is a tough nut to crack. The atoms pair up with a triple bond, very difficult for humans to break without a lot of heat and pressure. Fortunately, this makes it very inert for the atmosphere, but life needs to get at it to make amino acids, muscles, organs, and more. Nitrogenase enzymes in some microbes, such as soil bacteria, are able break apart the atoms at ambient temperatures (a secret agricultural chemists would love to learn). They then "fix" nitrogen into compounds such as ammonia (NH3) that can be utilized by plants and the animals that eat them. To have a nitrogen cycle, though, something has to return the N2 gas back to the atmosphere. That's the job of anammox bacteria.

Most nitrogen on earth occurs as gaseous N2 (nitrogen oxidation number 0). To make nitrogen available for biochemical reactions, the inert N2 has to be converted to ammonia (oxidation number −III), which can then be assimilated to produce organic nitrogen compounds, or be oxidized to nitrite (oxidation number +III) or nitrate (+V). The reduction of nitrite in turn results in the regeneration of N2, thus closing the biological nitrogen cycle.

Let's take a look at the enzyme that does this, the "hydrazine synthase multiprotein complex." Rocket fuel; imagine! No wonder the scientific community was surprised. The formula for hydrazine is N2H4. It's commonly used to power thrusters on spacecraft, such as the Cassini Saturn orbiter and the New Horizons probe that went by Pluto recently. Obviously, the anammox bacteria must handle this highly reactive compound with great care. Here's their overview of the reaction sequence. Notice how the bacterium gets some added benefit from its chemistry lab:

Our current understanding of the anammox reaction (equation (1)) is based on genomic, physiological and biochemical studies on the anammox bacterium K. stuttgartiensis. First, nitrite is reduced to nitric oxide (NO, equation (2)), which is then condensed with ammonium-derived ammonia (NH3) to yield hydrazine (N2H4, equation (3)). Hydrazine itself is a highly unusual metabolic intermediate, as it is extremely reactive and therefore toxic, and has a very low redox potential (E0′ = −750 mV). In the final step in the anammox process, it is oxidized to N2, yielding four electrons (equation (4)) that replenish those needed for nitrite reduction and hydrazine synthesis and are used to establish a proton-motive force across the membrane of the anammox organelle, the anammoxosome, driving ATP synthesis.

We've discussed ATP synthase before. It's that rotary engine in all life that runs on proton motive force. Here, we see that some of the protons needed for ATP synthesis come from the hydrazine reaction machine. Cool!

What does the anammox enzyme look like? They say it has tunnels between the active sites. The "hydrazine synthase" module is "biochemically unique." Don't look for a common ancestor, in other words. It's part of a "tightly coupled multicomponent system" they determined when they lysed a cell and watched its reactivity plummet. Sounds like an irreducibly complex system.

The paper's diagrams of hydrazine synthase (HZS) show multiple protein domains joined in a "crescent-shaped dimer of heterotrimers" labeled alpha, beta, and gamma, constituted in pairs. The machine also contains multiple haem units (like those in hemoglobin, but unique) and "one zinc ion, as well as several calcium ions." Good thing those atoms are available in Earth's crust.

Part of the machine looks like a six-bladed propeller. Another part has seven blades. How does it work? Everything is coordinated to carefully transfer electrons around. This means that charge distributions are highly controlled for redox (reduction-oxidation) reactions (i.e., those that receive or donate electrons). The choice of adverbs shows that their eyes were lighting up at their first view of this amazing machine. Note how emotion seasons the jargon:

Intriguingly, our crystal structure revealed a tunnel connecting the haem αI and γI sites (Fig. 3a). This tunnel branches off towards the surface of the protein approximately halfway between the haem sites, making them accessible to substrates from the solvent. Indeed, binding studies show that haem αI is accessible to xenon (Extended Data Fig. 4c). Interestingly, in-between the α- and γ-subunits, the tunnel is approached by a 15-amino-acid-long loop of the β-subunit (β245-260), placing the conserved βGlu253, which binds a magnesium ion, into the tunnel.

We would need to make another animation to show the machine in action, but here's a brief description of how it works. The two active sites, connected by a tunnel, appear to work in sequence. HZS gets electrons from cytochrome c, a well-known enzyme. The electrons enter the machine through one of the haem units, where a specifically-placed gamma unit adds protons. A "cluster of buried polar residues" transfers protons to the active center of the gamma subunit. A molecule named hydroxylamine (H3NO) diffuses into the active site, assisted by the beta subunit. It binds to another haem, which carefully positions it so that it is "bound in a tight, very hydrophobic pocket, so that there is little electrostatic shielding of the partial positive charge on the nitrogen." Ammonia then comes in to do a "nucleophilic attack" on the nitrogen of the molecule, yielding hydrazine. The hydrazine is then in position to escape via the tunnel branch leading to the surface. Once they determined this sequence, a light went on:

Interestingly, the proposed scheme is analogous to the Raschig process used in industrial hydrazine synthesis. There, ammonia is oxidized to chloramine (NH2Cl, nitrogen oxidation number −I, like in hydroxylamine), which then undergoes comproportionation with another molecule of ammonia to yield hydrazine.

(But that, we all know, is done by intelligent design.)


So here's something you can meditate on when you take in another breath. The nitrogen gas that comes into your lungs is a byproduct of an exquisitely designed, precision nanomachine that knows a lot about organic redox chemistry and safe handling of rocket fuel. This little machine, which also knows how to recycle and reuse all its parts in a sustainable "green" way, keeps the nitrogen in balance for the whole planet. Intriguing. Interesting. As Mr. Spock might say, fascinating.

Saturday 17 June 2017

Why the quest to reduce biology to chemistry is doomed.

The White Space in Evolutionary Thinking


Old CW chance and necessity did it/New CW gremlins did it

Evolution: The Fossils Speak, but Hardly with One Voice


The thinking planet?

Earth's Biosphere Is Awash in Information

Friday 16 June 2017

Stalinism redux? III

Russia’s Supreme Court Ruling Has Negative Impact on Jehovah’s Witnesses


Russia’s Supreme Court decision of April 20, 2017, is having a severe nationwide impact on Jehovah’s Witnesses. Authorities are violating the Witnesses’ fundamental freedoms and criminalizing their religious activities. At the same time, some Russian citizens interpret the decision as a license to discriminate against the Witnesses and even to subject them to hate crimes.

Russian Government Abuses and Restrictions on Human Rights

Criminal Charges Against Ministers of Jehovah’s Witnesses

On May 25, police raided the religious services of the Oryol Congregation of Jehovah’s Witnesses. The police arrested Dennis Christensen, a Danish citizen and an elder of the Oryol Congregation. Mr. Christensen is being held in pretrial detention until July 23 while the prosecutor attempts to build a case against him for “extremist activity.” If convicted, Mr. Christensen could be sentenced to a six-to-ten-year prison term.

Official Warnings Issued to Local Religious Organizations

On May 4, the prosecutor’s office issued a warning to the chairman of the Krymsk Local Religious Organization (LRO). The warning stated that the chairman and the members of the LRO can be subject to administrative and criminal liability for holding religious services.
Since the Supreme Court ruling, at least five other LROs have received similar warnings.
Police Raids on Religious Services

On April 22, police entered the Witnesses’ house of worship in Dzhankoy, Republic of Crimea, as religious services were concluding. The officers insisted that after the Supreme Court decision, the Witnesses had no right to meet together for worship. They searched the building and then sealed it to prevent its use for religious meetings.
Since the Supreme Court decision, there have been at least five other instances where police interrupted religious services of the Witnesses, one of which was held in a private home.
“I’m deeply concerned by this unwarranted criminalization of the peaceful activities of members of the Jehovah’s Witnesses communities in Russia. . . . I urge the Russian authorities to ensure that rights to freedom of religion or belief, freedom of opinion and expression, freedom of peaceful assembly and association of individuals belonging to the Jehovah’s Witnesses community are upheld, in compliance with the obligations of the country under international human rights law and OSCE [Organization for Security and Cooperation in Europe] commitments.”—Michael Georg Link, Director of the OSCE Office for Democratic Institutions and Human Rights.

Witness Schoolchildren Targeted

On April 24, in the village of Bezvodnoye, Kirov Region, a teacher humiliated two young students whose mother is one of Jehovah’s Witnesses. The teacher justified her actions by stating that the Witnesses are banned in Russia.
On May 17, in the Moscow Region, a school principal issued a written warning to the parents of an eight-year-old student who had spoken about God to a classmate. The document referred to the Supreme Court decision and prohibited on school grounds “all actions that do not relate to the educational process.” The principal threatened to report the matter to the police and “to raise the issue of transferring the child to another form of training.”
Witness Men Denied Alternative Civilian Service

On April 28, the Conscription Commission of the Cheboksary and Marposadskiy regions rejected the application of one of Jehovah’s Witnesses for alternative service. The Commission stated that Jehovah’s Witnesses are “extremist” and cannot be granted alternative service.
At least two other male Witnesses similarly had their applications for alternative civilian service denied.
Philip Brumley, general counsel for Jehovah’s Witnesses, noted the contradiction in the government’s stance: “On the one hand, the government refuses alternative civilian service to young Witnesses because they are ‘extremists,’ while on the other hand, it demands that these ‘extremists’ be inducted into the army. Does it make sense that the government would allow ‘extremists’ to be in the army?”

Societal Abuses and Discrimination

Acts of Violence Against Witnesses

On April 30, in Lutsino, Moscow Region, the home of a Witness family was burned to the ground, along with the adjoining home of their elderly parents. The arsonist had first expressed his hatred for the family’s religion and then started the fire.
On May 24, in Zheshart, Komi Republic, arsonists caused significant damage to a building used by Jehovah’s Witnesses for religious services.



Kingdom Hall in Zheshart damaged by arson


At least nine other houses of worship have been vandalized since the Supreme Court decision of April 20, 2017.
On April 26, one of Jehovah’s Witnesses in Belgorod was leaving his home when an attacker yelled, “You have been banned!” and then he beat the Witness.
On May 11, a group of men interrupted the religious services of Jehovah’s Witnesses in Tyumen and, using obscene and insulting language, threatened to harm the attendees.
Witnesses Dismissed From Employment

On May 15, the management of a chemical factory in Dorogobuzh, Smolensk Region, dismissed all of its employees who are Jehovah’s Witnesses. The management explained that they had received an order from the FSB to dismiss all of the Witnesses because “extremists” cannot work at the factory.

In at least three other incidents since the Supreme Court decision, Witness employees have been threatened with dismissal because they belong to an “extremist” religion. In the village of Yashkino, Kemerovo Region, the police pressured one Witness, but she refused to divulge information on other Witnesses. The officers said that it was unlawful to be a member of a banned religion and likened Jehovah’s Witnesses to ISIS terrorists.

Concern for the Welfare of Jehovah’s Witnesses in Russia

In the ten years leading up to the Supreme Court decision, Jehovah’s Witnesses in Russia were  victims of a government-sponsored attack against their religious freedom that subjected them to much harassment. Now in the aftermath of the decision, their security is even less certain. The decision vilifies the Witnesses and has emboldened some individuals and government officials to inflict further harm, as exemplified by these recent incidents. Jehovah’s Witnesses worldwide are greatly concerned about what will happen to their fellow Witnesses in Russia if the Appellate Chamber of the Supreme Court upholds the decision when it considers the case on July 17, 2017.

Mr. Brumley stated: “No one has presented any evidence that even remotely links Jehovah’s Witnesses with extremism. The alleged danger that the Witnesses are accused of posing to society is in no way commensurate with the persecution they have already endured. Russia needs to rethink its actions against Jehovah’s Witnesses in light of its constitution and its international agreements that guarantee religious freedom.”



Ragnarok for the RNA world?

As a Solution to the Origin of Life, RNA World Model Comes Under Attack

According to a recent article at New Scientist, "Why 'RNA world' theory on origin of life may be wrong after all," the RNA world model of the origin of life is under attack:
Life has a chicken-and-egg problem: enzymes are needed to make nucleic acids -- the genetic material -- but to build them you need the genetic information contained in nucleic acids. So most researchers assume that the earliest life, long before the evolution of cells, consisted of RNA molecules. These contain genetic information but can also fold into complex shapes, so could serve as enzymes to help make more RNA in their own image -- enabling Darwinian evolution on a molecular level.
At some point, the idea goes, this RNA world ended when life outsourced enzymatic functions to proteins, which are more versatile. The key step in this switch was the evolution of the ribosome, a structure that builds protein molecules from genetic blueprints held in RNA.
But such a transition would require abandoning the enzymatic functions of RNA and reinventing them in proteins. "That is not a simple model," says Loren Williams, a biochemist at the Georgia Institute of Technology in Atlanta.
That's a reasonable point at the end of the quote: If a self-replicating system has all of the enzymatic functions it needs from RNAs (something that hasn't been demonstrated), then rebuilding that system using an entirely different type of molecule (proteins) would be an extremely difficult task and highly unlikely. Yet this is essentially precisely what the classical RNA world model requires.
But there are many other criticisms of the RNA world model. A 2012 paper inBiology Direct by biochemist Harold S Bernhardt keenly titled, "The RNA world hypothesis: the worst theory of the early evolution of life (except for all the others)," notes that "the following objections have been raised to the RNA world hypothesis":
(i) RNA is too complex a molecule to have arisen prebiotically; (ii) RNA is inherently unstable; (iii) catalysis is a relatively rare property of long RNA sequences only; and (iv) the catalytic repertoire of RNA is too limited.
Now the author himself accepts the view that the RNA world is the best materialistic model for the origin of life. But he's very frank about its problems. For example, regarding the objection that "RNA is too complex a molecule to have arisen prebiotically," he writes:
RNA is an extremely complex molecule, with four different nitrogen-containing heterocycles hanging off a back-bone of alternating phosphate and D-ribose groups joined by 3',5' linkages. Although there are a number of problems with its prebiotic synthesis, there are a few indications that these may not be insurmountable. Following on from the earlier work of Sanchez and Orgel, Powner, Sutherland and colleagues have published a pathway for the synthesis of pyrimidine nucleotides utilizing plausibly prebiotic precursor molecules, albeit with the necessity of their timed delivery (this requirement for timed delivery has been criticized by Benner and colleagues, although most origin of life models invoke a succession of changing conditions, dealing as they do with the evolution of chemical systems over time; what is critical is the plausibility of the changes).
We covered the research of Powner and Sutherland here and here, pointing out that it was carefully designed to yield the desired results and noting how the goal-directed nature of the experiment undermines claims of the model's plausibility under unguided natural conditions. Hence the criticism that it has an unlikely "requirement for timed delivery."
Bernhardt then moves on to another criticism:
RNA is often considered too unstable to have accumulated in the prebiotic environment. RNA is particularly labile at moderate to high temperatures, and thus a number of groups have proposed the RNA world may have evolved on ice, possibly in the eutectic phase (a liquid phase within the ice solid).
But there's a major problem with the "cold" origin of life hypothesis: at low temperatures, reactions become so slow that nothing interesting ever happens. That's going to be a problem for many types of organic chemistry necessary for the origin of life. This is an especially significant problem when one considers that life appeared on earth very rapidly after conditions became favorable:
"...we have now what we believe is strong evidence for life on Earth 3,800 thousand million years [ago]. This brings the theory for the Origin of Life on Earth down to a very narrow range ... we are now thinking, in geochemical terms, of instant life..." (C. Ponnamperuma,Evolution from Space 1981.)
"[W]e are left with very little time between the development of suitable conditions for life on the earth's surface and the origin of life. Life is not a complex accident that required immense time to convert the vastly improbable into the nearly certain. Instead, life, for all its intricacy, probably arose rapidly about as soon as it could." (Stephen Jay Gould, "An Early Start," Natural History, February, 1978.)
A cold origin of life makes it much more difficult for life to arise under such a short timescale. Moreover, the notion that the early earth was cold rather than hot flies in the face of everything geologists have ever said about the conditions on the early earth.
Next, Bernhardt notes that "Catalysis is a relatively rare property of long RNA sequences only," and he offers a nice discussion of the gross improbability of randomly producing a long, self-replicating RNA molecule:
The RNA world hypothesis has been criticized because of the belief that long RNA sequences are needed for catalytic activity, and for the enormous numbers of andomized sequences required to isolate catalytic and binding functions using in vitro selection. For example, the best ribozyme replicase created so far -- able to replicate an impressive 95-nucleotide stretch of RNA -- is ~190 nucleotides in length, far too long a sequence to have arisen through any conceivable process of random assembly. And typically 10,000,000,000,000-1,000,000,000,000,000 randomized RNA molecules are required as a starting point for the isolation of ribozymic and/or binding activity in in vitro selection experiments, completely divorced from the probable prebiotic situation. As Charles Carter, in a published review of our recent paper inBiology Direct, puts it:
"I, for one, have never subscribed to this view of the origin of life, and I am by no means alone. The RNA world hypothesis is driven almost entirely by the flow of data from very high technology combinatorial libraries, whose relationship to the prebiotic world is anything but worthy of "unanimous support". There are several serious problems associated with it, and I view it as little more than a popular fantasy" (reviewer's report in [5]).
1014 - 1016 is an awful lot of RNA molecules.
Don't miss what's being said here: the argument directly parallels ID proponents who observe that it's extremely unlikely for an RNA molecule with just the right nucleotide sequence needed for self-replication to arise by chance. In other words, he's making the information sequence challenge to the origin of life.
Now Bernhardt proposes that perhaps the first self-replicating RNA was much shorter, reducing the probabilistic obstacles to randomly generating the right nucleotide sequence. But the evidence that this is actually possible is non-existent. Indeed, one of the reviewers, Eugene Koonin, points out that such a self-replicating RNA -- whether long or short -- has yet to be demonstrated:
I basically agree with Bernhardt. The RNA World scenario is bad as a scientific hypothesis: it is hardly falsifiable and is extremely difficult to verify due to a great number of holes in the most important parts. To wit, no one has achieved bona fide self-replication of RNA which is the cornerstone of the RNA World.
Finally, Bernhardt explains a fourth problem with the RNA world model, namely "The catalytic repertoire of RNA is too limited":
It has been suggested that the probable metabolic requirements of an RNA world would have exceeded the catalytic capacity of RNA. The majority of naturally occurring ribozymes catalyze phosphoryl transfer reactions -- the making and breaking of RNA phosphodiester bonds. Although the most efficient of these ribozymes catalyze the reaction at a comparable rate to protein enzymes -- and in vitro selection has isolated ribozymes with a far wider range of catalytic abilities -- the estimate of proteins being one million times fitter than RNA as catalysts seems reasonable, presumably due to proteins being composed of 22 chemically rather different amino acids as opposed to the 4 very similar nucleotides of RNA.
While Bernhardt discusses the various kinds of reactions that RNA can catalyze, he admits "RNAs are, in most cases, worse catalysts than proteins." That sounds like Bernhardt just conceded the validity of the criticism that he described against the RNA world. Somehow, however, he manages to spin the inferiority of RNA catalysis, turning it into not a knock against the RNA world, but an argument for it: "This [the inferior catalytic abilities of RNA] implies that their [RNA's] presence in modern biological systems can best be explained by their being remnants of an earlier stage of evolution, which were too embedded in biological systems to allow replacement easily."
So RNA is used by living organisms -- despite its inferior catalytic abilities -- only because evolution wasn't able to replace it? But aren't we constantly told how proteins can evolve to accommodate virtually any need of an organism? Doesn't this suggest severe limits to the evolvability of proteins? Now it seems that limits to evolution have become an argument forevolution.
This tortured logic brings us back to the criticism raised in the recent New Scientist article: the RNA world model is unlikely to be correct because it requires that proteins (with superior chemistry-catalyzing abilities) somehow swooped in and replaced what RNA was doing. That seems very unlikely. But Bernhardt again tries to spin this dilemma into an argument for the RNA world -- that difficulties replacing RNA with protein point to the fact that RNA was once a precursor of life. However, if it's so hard to replace RNA with proteins, how do we know that it happened in all the other cases required by the RNA world model?
It seems that whether proteins did or did not replace RNA, we're being told that in either case that's evidence for the RNA world. No wonder Eugene Koonin called the model "unfalsifiable."
So why does anyone prefer the RNA world model, given all its problems? Koonin provides the answer in his reviewer's comments at the end of Bernhardt's article -- it's because he requires some materialistic model, and other materialistic models clearly won't explain the origin of replication:
[T]he RNA World appears to be an outright logical inevitability. 'Something' had to start efficiently replicating to kick off evolution, and proteins do not have this ability.
Koonin's argument thus goes like this: We know that unguided evolution is true, so some evolutionary model must be correct. If other unguided models of life's origins won't work, then the RNA world must be correct, because "something" had to happen to get life started.
But what if the RNA world itself has many problems and so it isn't a viable solution? That's not an option Koonin seems willing to consider. He's right that "something" has to get life started. But there is a third way that Koonin hasn't considered. That third way -- the "something" he won't consider -- is the only known cause that can generate the kind of highly complex and specified digital sequences required at the origin of life: intelligent design.