Brief Biochemistry of Brazzein, a Sweet Tasting Protein

This protein was quite fun in modelling considering its secondary structures. I will admit though that I have a newfound appreciation for molecular chaperones, the proteins that assist with non-covalently folding other proteins. Below is an example of my brazzein wire model:

Derived from the berries of a West African plant, the Pentadiplandra brazzeana Baillon, brazzein is one of the sweetest and the smallest of the sweet tasting proteins. In fact, this 54 amino acid long protein can be 500 to 2000 times sweeter than sucrose. The presence of PyrE (pyroglutamic acid) at the N-terminus of brazzein is known to cap sweetness at the lower aformentioned levels, thus cleaving PyrE increases sweetness. So far, studies have shown that only humans and Old World primates can taste brazzein’s sweetness. This occurrence is best explained by the activation of human sweet receptors, heterodimeric G-protein coupled receptors (GPCRs), by brazzein.

The structure of brazzein plays a critical role in sweetness. As with most other proteins found in nature, the most common stereoisomer of this protein is the L-enantiomer. The D-enantiomer, or the mirrored image, can be prepared by synthesizing brazzein with the fluoren-9-yl-methoxycarbonyl (Fmoc) solid-phase method, a pepetide synthesis technique originally developed by Robert Bruce Merrifield. Interestingly enough,  D-brazzein has no sweetness and was in fact tasteless most likely due to minimal to no human taste receptor binding. The counterpart L-brazzein is quite a hardy protein with exceptional heat and pH stability maintaining its sweetness at a high of 98°C for two hours in a pH range of 2.5-8. This stability is mainly credited by its four intramolecular disulfide bonds and no free sulfhydryl groups.

Ironically, the brazzein fold comprising of one bent alpha helix and three strands of antiparallel beta-sheets shares the same Scorpion-toxin like domain as some small potent scorpion toxins such as TsKapa, a potassium channel blocker. A structural resemblance is also found in plant gamma-thionins and defensins yet this sweet protein has no published harmful side effects when consumed.

P&S

References

Hellekant, G. & Danilova, V. (2005). Brazzein a Small, Sweet Protein: Discovery and Physiological Overview. Chemical Senses, 30(suppl 1), i88-i89.

Assadi-Porter, F. M., Maillet, E. L., Radek, J. T., Quijada, J., Markley, J. L. & Max, M. (2010). Key amino acid residues involved in multi-point binding interactions between brazzein, a sweet protein, and the T1R2-T1R3 human sweet receptor. Journal of Molecular Biology, 398(4), 584–599.

Caldwell, J.E,, Abildgaard, F., Dzakula, Z., Ming, D., Hellekant, G. & Markley, J.L. (1998). Solution structure of the thermostable sweet-tasting protein brazzein. Natural Structural Biology, 5(6), 427-31.

Izawa, H., Ota, M., Kohmura, M. & Ariyoshi, Y. (1996). Synthesis and characterization of the sweet protein brazzein. Biopolymers, 39(1), 95-101.

Brief Biochemistry of Melittin, a Toxin from Bee Venom

One protein structure that I have been wire modelling quite a bit is melittin, a toxin from honey bee (Apis mellifica) venom (examples below):

Melittin is a 26 amino acid peptide made of two alpha helical sections with a nonpolar N-terminus and a polar C-terminus. This structure resembles a bent rod most likely due to proline-14 causing helix destabilization. Given its structure, it is most often studied as a water-soluble tetramer when isolated at high concentrations in bee venom and a monomer at the lowest concentrations known for cell membrane disruption.

To elucidate, the toxicity of melittin on exposed cells comes from biochemical activities that are hardly mentioned in general discussion. As general knowledge, the most prevalent cause of accidental fatalities from bee venom stings results from allergic reactions in hypersensitive people. However, this lethal reaction is the result of phospholipase A2 and in some cases hyaluronidase. There are a myriad of other toxins in bee venom, such as melittin, that are weakly allergenic, yet still cause biochemical aberrations.

Specifically, melittin has the ability to inhibit some Ca(2+)/calmodulin kinases and ion transport pumps such as NA(+)/K(+) ATPase, thus increasing the cell membrane permeability to ions. In addition, negatively charged membrane lipids are an attractant to melittin, thus favoring melittin incorporation into the membrane leading to cell lysis.

Given the aberrant changes in cell structure from this protein, several complex mechanisms have been observed in bees to prevent autolysis by melittin. This protein is derived from a prepromelittin precursor that underwent a 21-amino acid signal peptide cleavage to form promelittin. Further processing occurs after promelittin is secreted into the bee venom sac to protect the bee from the damaging lytic effects of melittin.

P&S

References

Strong, P. N. & Wadsworth, J. D. F. (2000). Chapter 9:  Pharmacologically Active Peptides and Proteins from Bee Venom. In Rochat, H. & Marie-France Martin-Eauclaire M. (Ed. 1) Animal Toxins: Facts and Protocols. (127-151). Basel Switzerland:  Birkhäuser Verlag.

Terwilliger, T. C. & Eisenberg, D. (1981). “The Structure of Melittin” The Journal of Biological Chemistry, 257(11), 6016-22.

Yang, S. & Carrasquer, G. (1997). “Effect of melittin on ion transport across cell membranes”. Zhongguo Yao Li Xue Bao, 18 (1), 3–5.

Bite the Bullet Brownies

Today, I stumbled upon these chocolate treats with a playful, and risky twist:

Bite the Bullet and Chocolate Russian Roulette, both chocolate-based games of chance, seem to be quite popular in Great Britain, but haven’t really been generating interest on the other side of the pond. Both games include 12 numbered bullet-shaped chocolates in which one of those chocolates has an extremely hot pepper.  Players take turns using a numbered die or a spinner to determine which corresponding numbered chocolate to eat, hopefully being spared from the hot pepper! I am always making hot pepper brownies and I never thought to make a game out of it!  My brownies are kicked up with Habanero peppers, Scotch Bonnets or whatever I can find. It may be more entertaining though to use some Bhut Jolokia peppers for this game though to boost the capsaicin levels–don’t worry, the spiciness level drops during baking so it will be bearable ;). I might have to cook a batch of brownies and hot pepper brownies, mold pieces into bullet shapes, then try out a few rounds of Bite the Bullet with some friends! By the way, I only like cooking brownies from scratch, so I have included the brownie recipe below. A friend of mine’s gave me that recipe and told me it was the best yet, and I agree!

Homemade Brownie Recipe
1 cup (225 g) butter, melted
3 cups (600 g) white sugar
1 tablespoon (15 mL) vanilla extract
4 eggs (add one more for a cakier result)
1 1/2 cups (180 g) all-purpose flour
1 cup (70 g) unsweetened cocoa powder
1/2 teaspoon salt
1/2 teaspoon baking soda (to give a crust – omit if you don’t want that)
1 cup (182 g) semisweet chocolate chips
1/4 cup hot peppers, finely minced and deseeded (optional for hot pepper brownies)
Preheat oven to 350oF (175o C). Lightly grease a 9×13 baking dish with the paper from the butter. Melt butter in the microwave or on the stovetop.
Combine the melted butter, sugar, and vanilla in a large bowl. Mix. Beat in the eggs, one at a time, mixing well after each, until thoroughly blended. Sift together the flour, baking soda, cocoa powder, and salt. Gradually stir the flour mixture into the chocolate mixture until blended.
Toss the chocolate chips and minced peppers in a light dusting of flour, and stir into the mix with a spoon or spatula. The flour will keep them suspended in the batter and prevent them from all sinking to the bottom!
Pour into prepared pan. Spread the batter in the pan, slightly mounding on the sides so it will all bake evenly (avoiding the typical mound you get in the middle after baking). Bake for 35-40 minutes.
Brownies are done with a toothpick or skewer inserted in the middle comes out clean.
Let the brownies cool and keep the brownies in the pan.

Enjoy!

P&S

Awkward Sayings in Science

Hello again, so far I have been able to post two blogs in one night, which is a miracle considering my previous track record. Recently, I have been writing in a notebook some awkward sayings that I have been either caught saying or thought about and jotted down. There is a lot of jargon that gets thrown around
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New Beginnings: Chemistry and Relationships

I have been wanting to blog again for quite some time now (my last 2 blogs did not last very long, and it has been years since then), but I never found the motivation to sit down and spend a few minutes blogging about my thoughts. To be honest, I think the main contributor to this lack of motivation was my unfailing ability to forget my password. As a side note, I am still locked out of my first blog on Blogspot (now called Blogger) started in 2008. After looking around my room and realizing that my thoughts were strewn on random notebook pages and loose leaf paper, I decided it was time to blog it all out. Therefore, this blog will be dedicated to my random thoughts on science, life, and experimental jewelry designs for my Etsy shop PeachesandScience (https://www.etsy.com/shop/PeachesandScience for protein structure jewelry goodies)! If I don’t blog again within the next few months, poke me with a stick. Below is a post I put on Facebook a few weeks ago about the relationship between chemistry and relationships that I have been meaning to blog about but Facebook was the closest thing -.- … Anyway, check it out:

As I was listening to the radio today, I had an “ah-hah!” nerd moment about what chemistry can teach us about some relationships. So the radio host was talking about how a female singer allegedly had an affair with Jay Z a few months ago. Neither him nor his wife Beyonce are causing a scene about this rumor as if nothing ever happened.

That had me thinking lol! Let’s say that the affinity for electrons to bond with other electrons is like a person connecting to another person. Electrons like to be happy, and it is commonplace for electrons to break bonds between atoms to bond to another atom (or atoms) that they are more happy with. When electrons are stressed out or overexcited, the resulting molecule can be quite reactive, such as with reactive oxygen species. These reactive molecules will travel through an organism and take what it needs from other molecules, leaving them damaged with weak or unstable bonds.

If I were to use this analogy for people, I would say that people make and break bonds with others all of the time. Being quick to act reactively and break bonds with others just to create stability within one’s own life may cause more instability and irreversible damage for those others.

I hate to say it, but carbon (an important element in our bodies) is considered a “loose” molecule in the periodic table bonding with whomever it pleases and breaking up when the bond wasn’t good enough. If it didn’t give it up so easy, we wouldn’t be here right now! Holding onto a weak relationship may do more harm than good, even though being “loose” has its own problems lol. That is one of the reasons why silicon-based life wouldn’t work as well here on earth because silicon wants too much stability and i[s] quite reactive when it doesn’t get its way (sounds like my ex-boyfriend…).

It’s not about how many bonds were made or broken, it’s about how strong of a bond it was. If someone you are close to has an affinity towards someone else, it may be because your bond was not as strong as you thought. Think about this:  two nitrogen atoms triple bonded to each other forms one of the strongest bonds in chemistry, according to their bond-dissociation energy (a measurement of bond strength). I like to think of a triple bonded relationship as a bonding of the mind, body and spirit—a bond that reactive people will have a hard time breaking apart.

I am neither Jay Z nor Beyonce so I don’t know anything of their current relationship as a married couple, but their bond appears to be unbroken after this scandal took place—they may be triple bonded. So, if this applies to you or not, I will give this question to ponder: how strong are your bonds with the people in your life?

– August 7, 2013, LM via Facebook

That is all for tonight, till next time, take care!

P&S