The year is 2442. Protein engineering and molecular biology have become incredib
ID: 3165448 • Letter: T
Question
The year is 2442. Protein engineering and molecular biology have become incredibly powerful and all diseases are cured. Biochemists now spend their time on an obsessive hobby: racing motor proteins on the cytoskeleton and gambling with their lab mates. You are short on money and want to gain an unfair advantage over your competitors. All races are done in vitro, in which purified proteins and other additives are mixed in a test tube. A single one micrometer-long cytoskeleton fiber is placed in the tube, and a single motor protein is added to one end of the fiber. Whoever gets their motor protein to the other end of their fiber first, wins. Each racer gets to decide the following for their racing setup: 4. 1. Which cytoskeleton fiber protein they use. » 2. Which motor protein thev use, 3. Which end of the fiber the motor protein is added to for the start of the race (+ or -). 4. Other chemicals that are added to the mixture. *Explanation / Answer
A) Kinesins are motor proteins that act upon microtubules to move vesicles and organelles within cells, cause the beating of flagella and cilia, and act within the mitotic and meiotic spindles to segregate replicated chromosomes to progeny cells. They convert chemical energy, typically in the form of ATP, into mechanical force. In essence, kinesins are ATPases. Generally, kinesins mediate plus-end transport, i.e., they move towards the (+) end of the microtubule. As such, it would be prudent to start our motor protein on (-) end. Kinesins exist as dimers, with a catalytic 'head' domain and a 'stalk/tail' domain that is important in interactions with the cargo molecules. The 'neck' attaches the stalk to the head and is essential in determining direction of motility and regulation of activity.
B) Kinesins are ATPases, i.e., they depend on hydrolysis of ATP to perform motoe functions. ATP binding and hydrolysis as well as ADP release change the conformation of the microtubule-binding domains and the orientation of the neck linker with respect to the head; this results in the motion of the kinesin. Replacing all ATP with non-hydrolyzable ATP, i.e., with AMP-PNP will result in termination of your own reaction, since the reactions governing the motion of kinesin are not able to proceed due to lact of ATP binding and hydrolysis.
It would be better to sabotage your competitor's setup with this molecule, in order to inhibit the ATP hydrolysis in their setup, thus preventing their motor protein from moving forward along the cytoskeletal fibre.
C) Myosins are a large family of motor proteins that share the common features of ATP hydrolysis (ATPase enzyme activity), actin binding and potential for kinetic energy transduction. Structurally, mysoins contain a 'head' domain that binds to actin filaments (microfilaments) and is the site of ATP hydrolysis. The movement of myosin along actin is regulated by tropomyosin and troponin on the actin filaments. In the original setup, calcium ions bind to troponin, thus causing tropomyosin to shift from the face of the actin filament to which myosin heads need to bind to produce contraction. Now, if you replace calcium chloride with sodium chloride, it would sabotage the setup because Calcium will not be present, which means that tropomyosin will remain attached to the face of actin, thus blocking myosin from it, which is essential to produce contraction. Thus, no movement will take place by myosin and this is why the sabotage worked so well.
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