Complex Protein Structures: Videos & Practice Problems

Proteins can form complex structures through interactions at binding sites, allowing them to create multi-protein complexes with diverse functions. These complexes are stabilized by disulfide bonds and non-covalent interactions. Protein shapes include helices, fibrous structures, and globular forms, which are essential for various cellular processes like DNA synthesis and ATP production. Understanding these dynamics is crucial for grasping protein functionality and cellular mechanisms.

Complex Protein Structures

Okay. So in this topic, we're going to be talking about complex protein structures. Proteins can form these very large complex structures that interact with other proteins and other molecules. I want to spend some time discussing how that happens. In order for proteins to form a bunch of different complex functions, how do they interact with each other? Well, typically, they interact through things called binding sites, which are just regions of the polypeptide chain that have sequences that allow them to interact with other polypeptide chains or larger proteins, and complexes. These binding sites allow for these polypeptide chains to come together, interact with each other, and form multi-protein complexes. These multi-protein complexes generally contain multiple polypeptide chains, and each one of these chains usually has some kind of different function, even if it's a slight difference. These structures are dynamic; they can assemble and disassemble in response to different extrinsic signals, cellular signals. Examples of these big multi-protein complexes include those involved in DNA synthesis, RNA processing, and ATP creation.

These multi-protein complexes have to be stabilized in some way. We've talked about this type of bond before. Do you remember what type of bond it is? It's a covalent bond, and it's really responsible for stabilizing protein complexes, or polypeptide chains together. These bonds are called disulfide bonds. Disulfide bonds are covalent bonds that stabilize protein structures and polypeptide chains. Nevertheless, it's not the only covalent bond involved. All the other bonds that form all the different structures that proteins can have are non-covalent bonds. If we were to look at what a complex or multi-protein complex might look like, consider an exosome protein made up of 6 proteins, each represented in a different color. These protein complexes come together, interact non-covalently or through disulfide bonds, to form these multi-protein complexes.

Proteins in multi-protein complexes can form really complex shapes. A couple of the shapes that they can form are helices, which are very common. A helix is the most energetically favorable way to link repetitive subunits together. They can also have elongated fibrous shapes, resembling a meshwork of springy but strong substances found a lot in skin or the extracellular matrix. Additionally, they can form compact globular shapes and have unstructured regions that provide flexibility. They can covalently cross-link to create meshworks, for instance, a protein called elastin, which is essential in skin. We are going to look at all the different ways that proteins can form. You can see that it can be of all different sizes, from this little tiny guy here to this big honker here, and they have all different shapes, such as linear shapes, circular shapes, and globular shapes. All these different protein shapes can form using multi-protein complexes of multiple polypeptide chains. So, let's move on.

What type of bonds hold polypeptide chains together to form complex proteins?

• A. Covalent bonds
• B. Phosphodiester bonds
• C. Ester bonds
• D. Noncovalent bonds

Answer: (D)

Due to the number of polypeptide chains, multiple protein complexes can only have a singular, globular shape.

• A. True
• B. False

Answer: (B)

Here’s what students ask on this topic:

What are the main types of bonds involved in stabilizing complex protein structures?

Complex protein structures are stabilized primarily by two types of bonds: disulfide bonds and non-covalent interactions. Disulfide bonds are covalent bonds formed between the sulfur atoms of cysteine residues, providing significant stability to the protein structure. Non-covalent interactions include hydrogen bonds, ionic bonds, van der Waals forces, and hydrophobic interactions. These non-covalent bonds are crucial for the dynamic assembly and disassembly of multi-protein complexes, allowing proteins to interact and perform various cellular functions.

How do binding sites facilitate the formation of multi-protein complexes?

Binding sites are specific regions on a polypeptide chain that allow proteins to interact with other proteins or molecules. These sites have unique sequences that enable the polypeptide chains to come together and form multi-protein complexes. The interactions at these binding sites can be stabilized by non-covalent bonds such as hydrogen bonds, ionic bonds, and van der Waals forces, as well as covalent disulfide bonds. This facilitates the formation of stable, functional multi-protein complexes essential for various cellular processes.

What are some common shapes that proteins can form?

Proteins can form several common shapes, including helices, fibrous structures, and globular forms. Helices are energetically favorable and often found in repetitive subunits. Fibrous structures are elongated and provide strength and elasticity, commonly found in skin and the extracellular matrix. Globular forms are compact and often involved in dynamic cellular processes. Additionally, proteins can have unstructured regions that offer flexibility and can covalently cross-link to create meshworks, such as elastin in the skin.

Why are disulfide bonds important in protein structures?

Disulfide bonds are crucial for stabilizing protein structures because they form strong covalent links between the sulfur atoms of cysteine residues. These bonds provide significant stability to the protein's three-dimensional structure, ensuring it maintains its functional shape. Disulfide bonds are particularly important in extracellular proteins, where they help maintain structural integrity under varying environmental conditions. They also play a role in the proper folding and stability of multi-protein complexes.

What role do non-covalent interactions play in protein complexes?

Non-covalent interactions play a vital role in the formation and stability of protein complexes. These interactions include hydrogen bonds, ionic bonds, van der Waals forces, and hydrophobic interactions. They allow proteins to interact dynamically, enabling the assembly and disassembly of multi-protein complexes in response to cellular signals. Non-covalent interactions are essential for the flexibility and functionality of protein complexes, facilitating various cellular processes such as DNA synthesis, RNA processing, and ATP production.