When do proteins change shape

The shape of a protein determines what it can interact with, just like the shape of a key determines which locks it can operate. Most of the proteins in your body can be grouped into four categories based on the function they carry out. Protein structure and variety Proteins are composed of chains of amino acids. National 5 Subjects National 5 Subjects up. Forms supporting frameworks inside cells and forms body structures. Tubulin: forms spindle fibres during mitosis and Keratin: the protein that makes up hair and nails.

Catalyse biological reactions. These metamorphic proteins change quickly and reversibly from one folded shape to another inside organisms. In fact, their ability to do so seems to be the key to their success.

Researchers at the Medical College of Wisconsin have now reconstructed the evolutionary history of a metamorphic human protein called XCL1. In one shape, it acts as a signaling molecule called a chemokine, binding to receptors on white blood cells and recruiting them to fight infections. But it can easily switch to a second shape that kills bacterial invaders as an antibiotic.

The Wisconsin researchers decided to learn about how metamorphic proteins evolve by looking at XCL1 more closely. Of the 46 chemokine proteins in humans, XCL1 is the only one that exhibits metamorphic switching. The others are stabilized by strong disulfide bonds that lock their protein molecules into a stable fold. But over the evolutionary history of XCL1, one of the disulfide bonds was lost, allowing a second conformation to emerge. Acacia Dishman , a graduate student, inserted the inferred DNA sequences into bacteria to resurrect the ancestral proteins.

Dishman found that the oldest ancestor had a single stable fold, the one common to all the chemokines. In proteins from a little later in the reconstructed evolutionary sequence, she detected two fingerprints, one for the ancestral fold but also one for a newer fold, although the new fold remained rare.

Surprisingly, just a little later in the evolutionary sequence, proteins showed the opposite: They were mainly folded in the new conformation and only rarely in the ancestral conformation. Finally, in the modern XCL1, the two conformations were about equal, Dishman found. But why would metamorphosis be better than having two specialized proteins? For example, valine is known by the letter V or the three-letter symbol val. Each amino acid is attached to another amino acid by a covalent bond, known as a peptide bond.

When two amino acids are covalently attached by a peptide bond, the carboxyl group of one amino acid and the amino group of the incoming amino acid combine and release a molecule of water. Any reaction that combines two monomers in a reaction that generates H 2 O as one of the products is known as a dehydration reaction, so peptide bond formation is an example of a dehydration reaction. Peptide bond formation : Peptide bond formation is a dehydration synthesis reaction.

The carboxyl group of one amino acid is linked to the amino group of the incoming amino acid. In the process, a molecule of water is released. The resulting chain of amino acids is called a polypeptide chain. Each polypeptide has a free amino group at one end.

This end is called the N terminal, or the amino terminal, and the other end has a free carboxyl group, also known as the C or carboxyl terminal. When reading or reporting the amino acid sequence of a protein or polypeptide, the convention is to use the N-to-C direction. That is, the first amino acid in the sequence is assumed to the be one at the N terminal and the last amino acid is assumed to be the one at the C terminal. Although the terms polypeptide and protein are sometimes used interchangeably, a polypeptide is technically any polymer of amino acids, whereas the term protein is used for a polypeptide or polypeptides that have folded properly, combined with any additional components needed for proper functioning, and is now functional.

Each successive level of protein folding ultimately contributes to its shape and therefore its function. The shape of a protein is critical to its function because it determines whether the protein can interact with other molecules. Protein structures are very complex, and researchers have only very recently been able to easily and quickly determine the structure of complete proteins down to the atomic level.

The techniques used date back to the s, but until recently they were very slow and laborious to use, so complete protein structures were very slow to be solved. To determine how the protein gets its final shape or conformation, we need to understand these four levels of protein structure: primary, secondary, tertiary, and quaternary.

Really, this is just a list of which amino acids appear in which order in a polypeptide chain, not really a structure. But, because the final protein structure ultimately depends on this sequence, this was called the primary structure of the polypeptide chain. For example, the pancreatic hormone insulin has two polypeptide chains, A and B. Primary structure : The A chain of insulin is 21 amino acids long and the B chain is 30 amino acids long, and each sequence is unique to the insulin protein.

The gene, or sequence of DNA, ultimately determines the unique sequence of amino acids in each peptide chain. So, just one amino acid substitution can cause dramatic changes. People affected by the disease often experience breathlessness, dizziness, headaches, and abdominal pain.

Sickle cell disease : Sickle cells are crescent shaped, while normal cells are disc-shaped. Secondary structures arise as H bonds form between local groups of amino acids in a region of the polypeptide chain. Rarely does a single secondary structure extend throughout the polypeptide chain.

It is usually just in a section of the chain. This holds the stretch of amino acids in a right-handed coil. Every helical turn in an alpha helix has 3. The tertiary structure of a polypeptide chain is its overall three-dimensional shape, once all the secondary structure elements have folded together among each other. Interactions between polar, nonpolar, acidic, and basic R group within the polypeptide chain create the complex three-dimensional tertiary structure of a protein.

When protein folding takes place in the aqueous environment of the body, the hydrophobic R groups of nonpolar amino acids mostly lie in the interior of the protein, while the hydrophilic R groups lie mostly on the outside. Cysteine side chains form disulfide linkages in the presence of oxygen, the only covalent bond forming during protein folding.

All of these interactions, weak and strong, determine the final three-dimensional shape of the protein. When a protein loses its three-dimensional shape, it will no longer be functional. Tertiary structure : The tertiary structure of proteins is determined by hydrophobic interactions, ionic bonding, hydrogen bonding, and disulfide linkages.

The quaternary structure of a protein is how its subunits are oriented and arranged with respect to one another. As a result, quaternary structure only applies to multi-subunit proteins; that is, proteins made from more than one polypeptide chain.

Proteins made from a single polypeptide will not have a quaternary structure. In proteins with more than one subunit, weak interactions between the subunits help to stabilize the overall structure. Enzymes often play key roles in bonding subunits to form the final, functioning protein.

For example, insulin is a ball-shaped, globular protein that contains both hydrogen bonds and disulfide bonds that hold its two polypeptide chains together. Four levels of protein structure : The four levels of protein structure can be observed in these illustrations. Denaturation is a process in which proteins lose their shape and, therefore, their function because of changes in pH or temperature.

Each protein has its own unique sequence of amino acids and the interactions between these amino acids create a specify shape. Pepsin, the enzyme that breaks down protein in the stomach, only operates at a very low pH.