Protein Stucture and Function

Proteins are extemely important molecules in living organisms which have a wide range of important functions. Your forum task is too investigate the structure and function of one protein.

1) Re-read the textbook section on proteins for back ground information

2) Watch the video below for further examples of possible structures

3) Research on the internet and find one example of a protein which is important in living organisms. You must attach a picture and also write a summary of at least 150 words about the structure and function of the protein.

IMPORTANT: You must not choose any protein from the textbook. You must not choose any protein already selected by a classmate and included in the forum.


DUE DATE: You must post your forum by the start of your second class during Week 29 (11/10/10)

Spectrin is a cytoskeletal protein found in the lining of the intracellular part of the plasma membrane, in pentagonal or hexagonal arrangements so as to form a scaffold to support the plasma membrane’s integrity and cytoskeletal structure, allowing flexibility. Spectrin can be found in erythrocytes, invertebrates and vertebrates. There are two alpha spectrins and five beta spectrins in vertebrate spectrin genes. Its structure is that of antiparallel coiled-coil repeats; their structure has a conformational rearrangement in one repeat, causing the movement of a loop. In all structures the link between them is alpha-helical, which have varying degrees of bending. Spectrin repeats form a three-helix bundle and can be found in various proteins involved in cytoskeletal structure. Only a little evidence for the role of spectrin in muscle tissue exists, such as in the myocardial cells where it has been found that they have a role in excitable tissue, and it is presumed it provides mechanical strength to cells.

A protein kinase is a kinase enzyme that modifies other proteins by chemically adding phosphate groups to them (phosphorylation). Phosphorylation usually results in a functional change of the target protein (substrate) by changing enzyme activity, cellular location, or association with other proteins. Protein kinases are also found in bacteria and plants. The chemical activity of a kinase involves transferring a phosphate group from a nucleoside triphosphate (usually ATP) and covalently attaching it to one of three amino acids that have a free hydroxyl group.

In mammalian cells, vinculin is a membrane-cytoskeletal protein in focal adhesion plaques that is involved in linkage of integrin adhesion molecules to the actin cytoskeleton. Discovered independently by Benny Geiger and Keith Burridge, its sequence is 20%-30% similar to α-catenin, which serves a similar function.
Vinculin is a 117-kDa cytoskeletal protein with 1066 amino acids. The protein contains an acidic N-terminal domain and a basic C-terminal domain separated by a proline-rich middle segment. Vinculin consists of a globular head domain that contains binding sites for talin and α-actinin as well as a tyrosine phosphorylation site, while the tail region contains binding sites for F-actin, paxillin, and lipids.
http://cmckb.cellmigration.org/figures/domain_vinculin.html (imagen de vinculin)
(Wikipedia)

coenzyme Q10 also known as ubiquinone is a powerful natural occuring compound, promoting chemical reactions and protecting the body from free radicals. Its more recognized effects are its antioxidant quialities in living beings as well as its control of the flow of oxygen within cells, assistance in cardiovascular functioning , the production of energy, the assistance in the absortion of other nutrients as well as good immune boosting properties. It is coenzyme Q10 the coenzyme for at least three mitochondrial enzymes as well as some other enzymes in the cell. These mitochondrial enzymes are of great importance for the production of ATP. In addition it has presented a great deal of help with cancer treatments due to its possitive properties.

In biology, histones are strongly alkaline proteins found in eukaryotic cell nuclei, which package and order the DNA into structural units called nucleosomes. They are the chief protein components of chromatin, act as spools around which DNA winds, and play a role in gene regulation. Without histones, the unwound DNA in chromosomes would be very long (a length to width ratio of more than 10 million to one in human DNA). For example, each human cell has about 1.8 meters of DNA, but wound on the histones it has about 90 millimeters of chromatin, which, when duplicated and condensed during mitosis, result in about 120 micrometers of chromosomes.

Actin is an unknown protein in contrast with others such as haemoglobin and keratin, it has a globular structure (globe-like) and it is the monomeric subunit of two types of filaments, these are microfilaments and thin filaments (which are part of the apparatus in muscle cells in charge of contracting). It is found in all eukaryotic cells, with the exception of the nematode sperm. Overall, Actin plays a fundamental and vital role in many cellular processes, almost always by means of interaction with other cellular membranes present in living organisms. These procedures are for example: muscle contraction, cell motility (or mobility), cell division, vesicle and organelle movement, cell signaling and last but not least the establishment of cell junctions and cell shape.
To conclude, we are able to observe that Actin is essential to us and other living organisms, as it takes part in many day to day processes inside our body that enables us live and survive correctly. In the link below you can see Actin’s globe-like structure:

http://commons.wikimedia.org/wiki/File:Actin_with_ADP_highlighted.png

Insulin is a protein that is used to regulate energy and glucose metabolism in the body. Insulin causes cells in the liver, muscle, and fat tissue to take up glucose from the blood, storing it as glycogen in the liver and muscle, so when there is an excess of glucose the insulin takes place to transform it into glycogen for storage. It also stops the use of fat as an energy source, as when it is absent, glucose won't be taken to the body cells and fat will start to be used as an energy source.
Insulin is composed of two peptide chains referred to as the A chain and B chain. A and B chains are linked together by two disulfide bonds, and an additional disulfide is formed within the A chain. In most species, the A chain consists of 21 amino acids and the B chain of 30 amino acids.

Rhodopsin, also known as visual purple, is a pigment of the retina that is responsible for both the formation of the photoreceptor cells and the first events in the perception of light. Rhodopsins belong to the G-protein coupled receptor family and are extremely sensitive to light, enabling vision in low-light conditions.Exposed to light, the pigment immediately photobleaches, and it takes about 30 minutes to regenerate fully in humans.
The vertebrate rod cell consists of an outer segment that contains a stack of rhodopsin-containing disc membranes connected to an inner segment via a ciliary process . The inner segment contains the metabolic machinery of the rod cell. Rhodopsin is synthesized in the endoplasmic reticulum and passes to the Golgi membranes where it becomes glycosylated. Rhodopsin-containing vesicles move from the Golgi to the outer segment where they fuse with the outer segment plasma membrane.

http://cas.bellarmine.edu/tietjen/Laboratories/Eye07.gif
FOTO

Lactate Dehydrogenase protein (LDH) is an enzime present in numerous kind of organisms, including plants and animals. This enzyme is an oxidoreductase that catalyzes the interconversion of pyruvate and lactate. As this can also catalyze the oxidation of hydroxybutyrate, it is sometimes called Hydroxybutyrate Dehydrogenase (HBD). There are 5 different isoenzymes of LDH (ffrom LDH1 to LDH5). Each is made out of 4 subunit which might be of 2 different types ;M and H subunit. These 2 subunits are encodeed by different genes(The M subunit is encoded by gene LDHA whilst the H subunit is encoded by LDHB). The isozymes differ in catalytic, physical and immunological properties. The function of this enzyme is an important step for energy production in cells, it is contained in many different type of cells around the body, such us in kedney, heart and liver. When cells die, LDH releases and goes into the blood. The average level of LDH in an organism varies with age; high ammount in chilhood (due to bone growth) and less as we get older. The binding coenzyme are considered in relation to known primary and tertiary structure of lactate dehtdrogenase. The adenine binds in a hydrophobic gap, and the 2 coenzyme phosphate are oriented by interaction with the protein. The positive charged guandinium group of arginine 101 then folds over the negative charged phosphates, collapsing the loop region over the active center and positioning the unreactive B side of the nicotinamide in a hydrophobic protein environment.

Myelin Basic Protein (MBP)

Myelin protein is very important in the process of myelination of nerves in the central nervous system. It is present in the bone marrow and in the immune system. It has a great role in demyelinating diseases, in particular, multiple sclerosis. The administration of MBP artificially increases blood-brain barrier permeability. Its main function is that it acts as an insulator to greatly increase the velocity of axonal impulse conduction. MBP is a hydrophilic protein that may function to maintain the correct structure of myelin.

Lactoferrin is a multifunctonal protein obtained from human milk, and in lesser concentration in cow milk. Arguably its main function is to transfer iron to cells around the body, however it also regulates the levels of free iron in external secretions and the blood. It is also a part of the immune system as it found in mucuses and kills bacteria and fungus, especially in human infants. Finally it reacts with DNA and RNA. Lactoferrin is found in human milk and also tears, saliva, nasal secretions, gall and in the blood.

Structure:
By using x-rays, scientists have determined that Lactoferrin is conformed by a single polypeptide chain made from 700 amino acids, forming two homologus globular domains named N-lobe and C-lobe, each lobe is further divided into two lobes N1 and N2, C1 and C2 respectively. Both lobes are connected by a short α helix.

Picture: