Further into Nardoo (cont'd Australian Expedition)

                My last post Beriberiand a Rough Australian Trip discussed the Wills-Burke expedition and the death of three out of four key participants due to a thiamine deficiency.  Near the end of that post, I explained that the men were eating foods rich in thiaminase I, which was breaking down any thiamine in their bodies.  Lack of the essential vitamin thiamine led to neurological disorders and was eventually fatal to all except John King.  One place that gave the men too much thiaminase I was fresh water mussels.  The other was nardoo, which is commonly prepared by the Aborigines without incident but was cooked incorrectly by the European explorers.

                I wanted to do a brief follow up to explain the differences in their preparations and why thiaminase I was still active in the European dish but was inactive in the Aborigine version.

                Nardoo is prepared from the plants of the genus Marsilea.  It is a fern but resembles a four-leaf clover (Figure 38.2).  The fronds, which are ground up to create a type of flour, are rich with thiaminase I.

               

                  Let’s take a step back and look more closely at the protein thiaminase I.

               

                  Figure 39.1 shows you a picture of the protein.  It is an enzyme, meaning that the protein helps a chemical reaction occur (Fun with Radioactivity post).  The particular reaction it catalyzes is shown in Figure 39.2.

                  In short, thiamine and another organic molecule (several molecules fit the bill here so the specifics aren’t important) bind to thiaminase I.  The enzyme then breaks thiamine into two pieces.  A broken thiamine is then unable to do its job in the body and leads to large problems, as demonstrated by Wills, Burke, King and Gray.

                 What are ways to ensure that this enzyme can’t do its job?

One: Destroy it.  I’ve told you previously that protein structure is essential for function (Cancerous Mutational Problems post).  If it doesn’t have the correct structure then it can’t do its job.  There are several ways to destroy protein's structure, but the simplest and most familiar one is heat.    Heat that protein up (ie. cook it)!  Heat is ruining that carefully folded protein and turning into a blob of amino acids with no function.

Think about when you cook an egg.  When it is first cracked, the whites are clear with a slightly yellow tinge.  As it cooks, the whites become opaque and stark in color.  Why?  You’re destroying all the protein inside the whites.  They are falling apart and forming a big clump of unfolded proteins.  It is safe to eat an egg after it has been cooked because any proteins in there are now dead and won’t function inside your body.  It’s also helpful to your digestive system, which further breaks down the proteins into their individual amino acids, transports them to cells, and your cells then use those amino acids to make new proteins that they need (Central Dogma post).  The circle of life.

Two: Take away its substrates.  Thiaminase I requires two things to function: thiamine and another organic molecule.  Clearly, minimizing thiamine is not an option, but it is possible to keep the other organic molecules to a minimum.  

Look at the cars outside.  They require two things to get them to move: gas and keys.  You can dip that entire car in gas but if there are no keys, you car isn’t going anywhere (unless you can hotwire a car, I suppose).  Same idea with thiaminase I.

                Our explorers went the route of #1 because that is how Europeans prepared grains: grinding and cooking.  Unfortunately, let’s quickly consider the Australian bush.  It’s HOT.   The proteins in the plant are going to be used to the hot temperatures so to destroy them, they must be cooked even hotter to mess up their proteins.  According to an article by Earl and McCleary in the journal Nature, these ferns can be boiled for 15 minutes and still have functional proteins.  That’s a hearty plant.

                The Aborigines choose route #2.  The plant is mixed with water and ground into a paste.  They are very careful to keep it away from anything else that might contain organic compounds and this minimizes how many organic molecules are present (how many keys are around to start the car).  Further diluting the paste with water ensures that if any organic molecules are present then they will be few and far between (spreading keys among 1,000 people as opposed to ten people).

                To be clear, no one knew exactly what the problem was with preparing nardoo.  It’s not like they held the plant up and said “Oh yes, there is thiaminase I here!  We will need to plan accordingly.”  It was obviously much more trial and error with preparation over time.  Whatever worked (and didn’t kill anyone) was kept around.  I would imagine it’s similar to discovering wild mushrooms or even rhubarb (the flesh of rhubarb is okay but the leaves are quite poisonous.  Crazy!).

Link to Protein Folding post, referenced in Figure 39.1.

REFERENCES

Earl and McClearly. “Mystery of the poisoned expedition.” Nature (1994) 368(6473) pgs 683 – 684.

Campobasso et al. “Crystal Structure of Thiaminase I- from Bacillus thiaminolyticus at 2.0 A Resolution.” 

Biochemistry (1998) 37, pgs 15981 – 15989. 

Protein images were created in PyMOL with PDB code 3THI

Beriberi and a Rough Australian Trip

         My other blog, Dr. Amedeo, is currently sporting a blurb about Aboriginal Australian ancestry (Ancient Humans post).  I thought an excellent parallel this week would be for this blog, Amedeo, to discuss the lost Australian expedition of 1860-1861 and how it relates to a problem called beriberi.

                Let’s meet the stars of the show.

                Robert O’Hara Burke

Born in Ireland, member of Australian army, police inspector

                William John Wills

Born in England, studied in Melbourne with interest in astronomy, meteorology and chemistry

                John King

                                Born in Ireland, military experience in India, camels

            

                Charles Gray

                                British sailor

                So what did these guys do?  In 1860, an expedition set out whose purpose was “for transversing the unknown interior of the Australian continent.”  While the coasts of Australia had been settled, the vast interior of the continent remained both unexplored and widely unknown.  The hopes for the expedition were to study the plants and animals of Australia as well as collect meteorological, geographical and astronomical data.  The leader would be one Robert O’Hara Burke and he chose William John Wills as his deputy.  They amply supplied themselves with both useful and illogical items.  Interestingly, the party became convinced that camels were essential to the journey since both deserts and the Australian bush were extremely hot (but had very little else in common).  

                No one had crossed Australia from the south to the north before so an added bonus of their trip would be the notoriety of being first to do so.  Unfortunately, competition for the title came in the form of John McDouall Stuart.  Burke became increasingly concerned that Stuart would beat his expedition (which was large and moved quite slowly), so he split the party by leaving groups behind in different places.  Eventually, the whittled entourage became Burke, Wills, Gray and King.  These four men took rations and successfully reached the north shore of Australia before Stuart.  

                This is where things start to go downhill for our explorers.  Monsoon season was upon them so traveling home was slow and rations were being depleted.  Their (arguably) biggest mistake was turning to the land, which they knew little about, to supplement their food supply.  Upon seeing signs of Aborigines eating mussels from a fresh water creek, our explorers procured some and ate.  They also began making nardoo, which is commonly made from a local fern by Aboriginal tribes.

                Not long after, Charles Gray died.  He had suffered on the journey home: he was unable to walk and spoke incoherently.  One night, he was found eating directly from their extremely depleted flour rations.  He had claimed he craved it and couldn’t help himself.  The others did not understand how he could steal from them, especially since the others were also finding their health to be failing.  Their legs felt paralyzed, they felt inexplicable exhaustion, pain and listlessness.

                Their exploration originally was large and those left behind knew Burke, Wills, Gray and King would need supplies on their return, so rations had been stored in known places.  These stores helped the men’s health greatly and their odd symptoms began to recede.  

                However, the men still wanted to supplement their supplies with food from the land so they went to back making nardoo. Burke and Wills would pound and clean the plant while King was out trying to collect more.  Hypothermia began to plague them in addition to fatigue, weakness, low pulse rates, and their bodies began to waste away.  Wills and Burke died.

                Miraculously, King was discovered by local Aborigines who nursed him back to health on a diet of nardoo, fish and local animals.  He was eventually rescued and returned to Melbourne, but his health was permanently damaged.

                What in the world was wrong with these men?

                They suffered from beriberi, which is a deficiency of thiamine (also called vitamin B₁, Figure 38.1).   This little molecule is essential to many cellular functions and must be obtained through our diet.  One of the first signs a body is lacking thiamine is neurological defects, such as confusion and irritability.  This eventually progresses to serious problems with the peripheral nervous system and cardiovascular problems followed by death.

                Unknowingly, the men were ingesting large amounts of thiaminase I, a protein whose job is to break down thiamine.  The mussels they ate were Velesunio ambiguus, which contain thiaminase I.  From the journals left behind, it is unclear whether the men cooked the mussels or ate them raw.  Proper cooking would have destroyed the protein and saved their health.  

   This is about to become a common theme.

                When nardoo is prepared by the Aborigines, ferns are ground into a thin paste, kept separate from other food, and diluted with water.  The expedition men ground their plants then boiled it in water.  The fern is full of thiaminase I (Figure 38.2).   The Aboriginal preparation ensured that thiaminase I was inactive.  The explorers way did not.  The men continued to eat the protein, which continued to break down any thiamine they were able to eat and their health plummeted.  Obviously when they recovered rations left behind, their health improved, but only went downhill again when they returned to nardoo.

                The most interesting part of all this was Gray’s eating of the flour.  Flour is full of thiamine.  Gray’s body clearly knew what it needed and forced him to crave the one food it knew had it.

                I had never heard of this story before listening to a podcast from “Stuff You Missed in History Class” from the website www.howstuffworks.com.  You can find it on iTunes by searching the podcast name and hunting through their archives of shows.  I highly recommend these podcasts if you have time in the car and get sick of music! 

Nardoo – a food prepared from the fern Marsilea Drummondii

Beriberi – a disease caused by a body’s deficiency in the vitamin thiamine

Vitamin – any organic molecule that is required by the body but the body cannot make itself (so it must be found in the diet)

Thiaminase I – a protein that breaks down thiamine

REFERENCES

http://adb.anu.edu.au/biography/burke-robert-ohara-3116

Earl and McClearly. “Mystery of the poisoned expedition.” Nature (1994) 368(6473) pgs 683 – 684.