ABC Transporters: Study with Video Lessons, Practice Problems & Examples

ABC transporters, or ATP binding cassette transporters, are integral membrane proteins that utilize ATP to pump substances against their concentration gradient, playing a crucial role in primary active transport. They consist of two transmembrane domains (TMDs) and two cytosolic nucleotide binding domains (NBDs) that hydrolyze ATP. Notably, some ABC transporters are multidrug resistance (MDR) transporters, which can confer antibiotic resistance in bacteria and remove anticancer drugs from human tumor cells, highlighting their significance in medical research and treatment strategies.

ABC Transporters

Hey guys. So here we're going to quickly revisit our map of the lesson on membrane transport. And we know that we're currently exploring the active transport branch, more specifically the primary active transport branch. And we've talked about the 5 types of ATPases including 2 very specific types of P-type ATPases, which are the sodium potassium pump and the calcium pump. And so now in our next video, we're going to talk even more details about the ABC transporters, one of the 5 types of ATPases. And so I'll see you guys in that video.

ABC Transporters

In this video, we're going to talk a little bit more details about one of the 5 types of ATPases, the ABC transporters. And so really the main takeaway of this video is that ABC transporters can provide multi-drug resistance. The ABC part of ABC Transporters stands for ATP-binding cassette. The ATP-binding cassette transporters or ABC transporters are really just integral membrane proteins with at least 1 ABC structural motif. Recall that motifs are just a combination or a pattern of secondary structures in proteins. Because ABC transporters are a type of ATPase, they are a form of primary active transport. So, it's no surprise that these guys pump substances across the membrane against their concentration gradient, from areas of low concentration to areas of high concentration.

Another defining feature of these ABC transporters is the structural elements that they contain. All ABC transporters share 2 common structural elements. The first is that they all contain 2 transmembrane domains or 2 TMDs for short. As their name implies, these are transmembrane, so they span the membrane, and that's going to help create a pore that allows them to transport molecules across the membrane. The second common structural element that all ABC transporters have is that they all have 2 cytosolic Nucleotide Binding Domains or 2 NBDs for short. These nucleotide binding domains will bind and hydrolyze ATP, which recall ATP is a nucleotide. Within these nucleotide binding domains, you can find the ATP-binding cassette, this specific structural motif.

If we take a look at our image down below, you can see the structure of this ABC transporter. Notice that spanning the membrane there are these 2 transmembrane domains here that we have highlighted in pink, and then on the cytosolic side of the cell, we have these 2 nucleotide binding domains or these 2 NBDs right here. The nucleotide binding domains can bind and hydrolyze ATP as we see here. It's also important to note that some ABC Transporters are called multidrug resistance or MDR transporters, which are particularly responsible for resistance to multiple drugs. In bacteria, MDR transporters confer antibiotic resistance. In humans, a protein called p glycoprotein or PGP, which is an MDR transporter, removes anticancer drugs from tumor cells. This is of great importance as MDRs can confer antibiotic resistance in bacteria, creating a significant health problem for humans. This is why a lot of research goes into MDR transporters, to see how we can work around those that are providing antibiotic resistance to bacteria that might be causing human health problems. Also, in humans, it's an area highly researched, as p glycoprotein here can remove anti-cancer drugs in tumor cells. That can be very problematic.

You'll notice this tiny little stethoscope over here on the left, which is a symbol that we're going to use moving forward in our course to represent something that you might want to pay close attention to, especially if you're going on into medical school or some other kind of medical profession like maybe pharmacy. Wherever we have this symbol, this is a place where you might want to hone in on and keep this idea in mind in case you encounter this idea again. If you are going on into medical school or some other kind of medical profession, this is an idea here that you'll probably revisit. If we take a look at our image down below, notice that we're showing you these red lines right here, that are taking toxins and drugs and pumping them to the outside of the cell. ABC transporters or MDR transporters can take toxins or drugs that are embedded within the plasma membrane and remove them, pump them to the outside of the cell, and they can also take drugs that are in the cytoplasm and toxins that are in the cytoplasm and remove them and pump them to the outside of the cell against their concentration gradient while utilizing and hydrolyzing ATP. This here concludes our lesson on ABC Transporters, and as we move forward in our course, we'll be able to get some practice applying these concepts. I'll see you guys in our next video.

ABC transporters are a part of a superfamily of transporters that have two nucleotide binding domains that bind __________, which is necessary for primary active transport.

• A. ADP.
• B. Phosphate.
• C. ATP.
• D. GTP.
• E. AMP.

What side of a membrane has a higher concentration of the toxin Limbricide after ABC transporter activity?

• A. Inside the cell.
• B. outside the cell.

Which of the following statements is TRUE for BOTH P-type ATPases and ABC transporters?

• A. They each have two ATP-binding protein domains.
• B. They both contain a phosphorylated Asp residue.
• C. They both are examples of multi-drug resistant proteins that pump toxins out of the cell.
• D. They are both dependent on the presence of ATP.
• E. They both require ATP binding before substrate binding and transport.

Here’s what students ask on this topic:

What are ABC transporters and how do they function?

ABC transporters, or ATP binding cassette transporters, are integral membrane proteins that utilize ATP to pump substances against their concentration gradient. They play a crucial role in primary active transport. Structurally, they consist of two transmembrane domains (TMDs) that span the membrane and two cytosolic nucleotide binding domains (NBDs) that hydrolyze ATP. The energy from ATP hydrolysis is used to transport molecules from areas of low concentration to high concentration, effectively moving substances against their natural gradient. This mechanism is essential for various cellular processes, including the removal of toxins and drugs from cells.

What is the significance of multidrug resistance (MDR) transporters in ABC transporters?

Multidrug resistance (MDR) transporters are a subset of ABC transporters that play a critical role in conferring resistance to multiple drugs. In bacteria, MDR transporters can lead to antibiotic resistance, posing significant challenges in treating bacterial infections. In humans, MDR transporters like P-glycoprotein (PGP) can remove anticancer drugs from tumor cells, making cancer treatment less effective. This dual role in both bacterial and human cells highlights the importance of MDR transporters in medical research, as understanding and potentially inhibiting these transporters could improve treatment outcomes for infections and cancer.

What are the structural elements common to all ABC transporters?

All ABC transporters share two common structural elements: two transmembrane domains (TMDs) and two cytosolic nucleotide binding domains (NBDs). The TMDs span the cell membrane, creating a pore that allows substances to be transported across the membrane. The NBDs, located on the cytosolic side of the cell, bind and hydrolyze ATP, providing the energy necessary for the transport process. These structural elements are essential for the function of ABC transporters, enabling them to move substances against their concentration gradient.

How do ABC transporters contribute to antibiotic resistance in bacteria?

ABC transporters contribute to antibiotic resistance in bacteria by actively pumping antibiotics out of bacterial cells, reducing the intracellular concentration of the drug. This action is primarily carried out by multidrug resistance (MDR) transporters, a subset of ABC transporters. By removing antibiotics from the cell, these transporters prevent the drugs from reaching their targets and exerting their effects, thereby allowing bacteria to survive and proliferate even in the presence of antibiotics. This mechanism is a significant factor in the development of antibiotic-resistant bacterial strains.

What role does P-glycoprotein (PGP) play in cancer treatment resistance?

P-glycoprotein (PGP) is an MDR transporter in humans that plays a significant role in cancer treatment resistance. PGP actively pumps anticancer drugs out of tumor cells, reducing the intracellular concentration of these drugs and thereby decreasing their efficacy. This action makes it difficult to achieve therapeutic drug levels within the tumor, leading to treatment failure and the development of drug-resistant cancer cells. Understanding the function of PGP is crucial for developing strategies to overcome drug resistance in cancer therapy.