Cell signalling: kinases & phosphorylation

Summary

This video script delves into the process of cellular signaling through phosphorylation, a key mechanism where proteins communicate via the transfer of phosphate groups. ATP serves as the phosphate donor, with kinases facilitating the attachment to specific amino acids like serine, threonine, and tyrosine. Phosphorylation acts as a signal flag, prompting protein interactions that can trigger cell division, migration, or death. The video also touches on the role of kinases in diseases like cancer and the potential for targeted drug therapies, promising a deeper exploration in subsequent episodes.

Takeaways

• 🔬 Phosphorylation is a process where a phosphate is added to a protein's amino acid, which is crucial for cellular signaling.
• ⚡ The primary source of phosphates for phosphorylation is ATP (adenosine triphosphate), a key energy molecule in cells.
• 🧬 Only three amino acids in humans—serine, threonine, and tyrosine—can typically be phosphorylated, with histidine phosphorylation being rare and more common in bacteria.
• 🧪 Kinases are proteins responsible for transferring phosphate groups from ATP to serine, threonine, or tyrosine.
• 🔄 Kinases are divided into serine/threonine kinases, tyrosine kinases, and dual specificity kinases, which can target all three phosphorylatable amino acids.
• 🚫 Some kinases have lost their ability to phosphorylate and are known as pseudokinases, though they may retain some activity under specific conditions.
• 📡 Phosphorylation acts as a signaling mechanism by attracting other proteins to the phosphorylated site, allowing for cellular interactions and communication.
• ⚠️ Hyperactive kinases can lead to excessive phosphorylation, which may contribute to diseases such as cancer.
• 🛠️ The ATP binding site in kinases is held in place by a glycine-rich loop and a lysine residue, which binds to the alpha and beta phosphates of ATP.
• 🧩 A conserved aspartate in the YRD/HRD motif of kinases is essential for transferring the gamma phosphate from ATP to a substrate protein, making it vital for kinase activity.

Q & A

What is phosphorylation and how does it relate to cellular signaling?

Phosphorylation is the process of transferring a phosphate group onto a specific amino acid within a protein. It is a key mechanism in cellular signaling, allowing proteins to transmit chemical signals to one another.

What is the source of phosphates for phosphorylation in cells?

The cell's source of phosphates is adenosine triphosphate (ATP), a molecule that provides chemical energy and is produced through cellular respiration involving food and oxygen.

Which amino acids can be phosphorylated in human cells?

In human cells, the amino acids that can be phosphorylated are serine, threonine, and tyrosine. Histidine can also be phosphorylated but this is less common in mammals.

What role do kinases play in the phosphorylation process?

Kinases are enzymes that can remove a phosphate group from ATP and attach it to specific amino acids in proteins. There are around 518 different kinases in a human cell, categorized into serine/threonine kinases, tyrosine kinases, and dual specificity kinases.

What is the significance of the DFG motif in kinases?

The DFG motif is crucial in kinases as it binds metal ions necessary for the phosphate transfer. It also forms the start of the activation loop, which determines the kinase's substrate specificity.

Why is the aspartate in the YRD motif important for kinase function?

The aspartate in the YRD motif is essential for the transfer of the gamma phosphate from ATP to the target amino acid on the substrate protein. Without it, the kinase can bind ATP but cannot perform the transfer.

How does phosphorylation lead to cellular responses like cell division or cell death?

Phosphorylation acts as a signal flag, attracting other proteins to bind to the phosphorylated site. This can initiate protein-protein interactions and signal transduction pathways, ultimately leading to various cellular responses including cell division, migration, or death.

What is the role of pseudokinases in cellular signaling?

Pseudokinases are a group of kinases that have lost their phosphorylation activity. While they do not phosphorylate proteins, some pseudokinases retain partial activity under certain conditions and may have regulatory roles in cellular signaling.

How can faulty kinase activity contribute to diseases like cancer?

Faulty or hyperactive kinases can lead to an overabundance of phosphorylation signals, which can cause uncontrolled cell division or other abnormal cellular behaviors, potentially contributing to diseases such as cancer.

What is the structural requirement for ATP to stay bound within the ATP binding pocket of a kinase?

For ATP to remain bound within the ATP binding pocket, it requires specific interactions with conserved amino acids such as the glycine-rich loop, a lysine residue, and a conserved glutamate that forms a salt bridge.

How are kinases targeted for drug development in treating diseases like cancer?

Kinases are targeted in drug development by designing drugs that can specifically inhibit their activity, thus reducing the overabundance of phosphorylation signals that may contribute to diseases like cancer.

Outlines

00:00

🧬 Cellular Signaling: Phosphorylation

This paragraph introduces the concept of cellular signaling through phosphorylation, a process where a phosphate group is added to specific amino acids in proteins. It explains that ATP, or adenosine triphosphate, serves as the source of phosphates. ATP is composed of an adenosine part and three phosphates (alpha, beta, and gamma). Proteins known as kinases are responsible for transferring the gamma phosphate to serine, threonine, or tyrosine residues on target proteins, a process critical for transmitting chemical signals. The paragraph also distinguishes between different types of kinases, including serine/threonine kinases, tyrosine kinases, and dual specificity kinases. It highlights the importance of phosphorylation in cellular processes such as cell division, migration, and death, and mentions the potential for kinase dysfunction to lead to diseases like cancer.

05:05

📢 Closing and Engagement

The second paragraph serves as a conclusion to the video, inviting viewers to subscribe and engage with the content by asking questions in the comments section. It sets up anticipation for the next video in the series, which will delve deeper into the role of kinases in diseases like cancer and explore targeted drug therapies.

Keywords

💡Phosphorylation

Phosphorylation is a key biochemical process where a phosphate group is added to a protein, often as part of a signaling pathway. In the context of the video, phosphorylation is crucial for cellular signaling, allowing proteins to communicate with each other. The script explains that certain proteins, known as kinases, can transfer a phosphate group from ATP to specific amino acids like serine, threonine, and tyrosine, thus altering the protein's activity and function within the cell.

💡ATP (Adenosine Triphosphate)

ATP is the primary energy currency of cells, used to power various cellular processes. The video script describes ATP as a molecule consisting of an adenosine part and three phosphate groups. It serves as the source of phosphates for phosphorylation. The gamma phosphate of ATP can be transferred to proteins by kinases, which is essential for signal transmission within cells.

💡Amino Acids

Amino acids are the building blocks of proteins. The video highlights that out of the twenty standard amino acids, only serine, threonine, and tyrosine can typically be phosphorylated in human cells. Histidine is also mentioned as a phosphorylatable amino acid, but this is less common in mammals. These amino acids play a pivotal role in cellular signaling as they can accept phosphate groups, thereby changing the protein's conformation and activity.

💡Kinases

Kinases are enzymes that catalyze the transfer of phosphate groups from ATP to proteins. The video script explains that there are around 518 different kinases in a human cell, which can be categorized based on the specific amino acids they phosphorylate: serine/threonine kinases, tyrosine kinases, and dual specificity kinases. Kinases are central to the process of cellular signaling as they modify proteins through phosphorylation, leading to various cellular responses.

💡Dual Specificity Kinases

Dual specificity kinases are a type of kinase that can phosphorylate both serine/threonine and tyrosine residues on proteins. The video script points out the interesting nomenclature, suggesting 'triple specificity' might be more accurate since these kinases recognize all three phosphorylatable amino acids. These kinases play a role in integrating different signaling pathways within the cell.

💡Pseudokinases

Pseudokinases are a group of kinases that have lost their phosphorylation activity but may still play a role in cellular regulation. The video script mentions that there are nearly 50 such kinases. Although they are called 'pseudokinases,' some retain a degree of activity under certain conditions, suggesting they might have evolved to perform other functions in the cell.

💡Phosphate Group

A phosphate group is a chemical unit consisting of one phosphorus atom and three oxygen atoms (PO4). In the video, the phosphate group is described as being transferred from ATP to proteins by kinases during phosphorylation. This transfer is a critical step in cellular signaling, as it modifies proteins and can lead to changes in their activity, interactions, and overall cellular function.

💡Cellular Signaling

Cellular signaling refers to the process by which cells communicate with each other and respond to their environment. The video script discusses how phosphorylation is one mechanism by which proteins transmit chemical signals within cells. This signaling is essential for coordinating various cellular activities, such as cell division, migration, and death.

💡Cell Division

Cell division is the process by which cells replicate their contents and split into two daughter cells. The video script mentions that phosphorylation, as part of cellular signaling, can lead to cell division. This process is tightly regulated and involves the activation of various proteins through phosphorylation, ensuring the correct segregation of genetic material and cellular components.

💡Cancer

Cancer is a group of diseases characterized by the uncontrolled growth and spread of abnormal cells. The video script touches on how faulty or hyperactive kinases can lead to an overabundance of phosphorylation signals, potentially contributing to the development of cancer. Understanding the role of kinases in cellular signaling is crucial for developing targeted therapies for cancer treatment.

💡Targeted Therapies

Targeted therapies are drugs designed to specifically interfere with particular molecules involved in the growth and progression of cancer cells. The video script suggests that understanding the role of kinases in cellular signaling can lead to the development of targeted therapies for diseases like cancer. These therapies aim to inhibit the activity of specific kinases, thereby reducing the uncontrolled cell growth associated with cancer.

Highlights

Proteins transmit signals through phosphorylation.

Phosphorylation is the transfer of a phosphate onto an amino acid within a protein.

ATP is the cell's source of phosphates for phosphorylation.

ATP consists of an adenosine part and three phosphates.

Proteins can transfer the gamma phosphate from ATP to specific amino acids.

Only serine, threonine, and tyrosine can be phosphorylated in humans.

Histidine can also be phosphorylated, but it's less common in mammals.

Kinases are the proteins that can perform phosphorylation.

There are around 518 different kinases in a human cell.

Serine and threonine are indistinguishable for kinases.

Dual specificity kinases can recognize all three phosphorylatable amino acids.

Pseudokinases are kinases that have lost their phosphorylation activity.

Phosphorylation acts as a signal flag for protein interactions.

Phosphorylation can lead to cell division, migration, and death.

Faulty kinases can cause diseases such as cancer.

Kinases have a structure with a pocket for ATP and mechanisms for phosphate transfer.

Conserved amino acids in kinases are crucial for ATP binding and phosphate transfer.

The DFG motif and activation loop determine kinase specificity.

The YRD motif is essential for the transfer of the gamma phosphate.

Kinases play a critical role in cellular signaling and behavior.

Kinases are potential targets for drugs in treating diseases like cancer.

Transcripts

How do proteins in your cells transmit signals to one another?

There are many types of signals, and many ways of transmitting them

and this is the first part in a series of videos where we'll explore some of the ways

that cellular signalling works.

Today we're going to look at phosphorylation.

When we say phosphorylation, we're talking about the transfer of a phosphate onto a particular

amino acid within a protein.

So let's start at the beginning, and have a look at what a phosphate is and where we

can get one.

Your cell's source of phosphates is a molecule called adenosine triphosphate, or ATP.

ATP is a source of chemical energy, and the production of ATP is one of the things

that happens when we eat food and breathe oxygen.

ATP consists of an adenosine part, and three phosphates (called the alpha, beta and gamma

phosphates).

While the chemical bonds in the adenosine part are really strong, the phosphates of

ATP are much less firmly attached, and some proteins are able pinch off the gamma

phosphate and stick it on the end of a particular amino acid.

This is called phosphorylation and it is a way in which proteins transmit chemical signals

to one another.

Out of the twenty different amino acids in your body, there are only three that can get

phosphorylated: serine, threonine and tyrosine.

Well, technically it's four, because histidine can get phosphorylated as well,

but it's more of a bacterial thing, it doesn't happen that often in mammals, and the mechanisms

of it are, frankly, a bit confusing.

The proteins that are able to pinch a phosphate off of ATP and stick it onto a serine, threonine

or tyrosine are called kinases.

There are around 518 different kinases in a human cell, so you'd expect them to be split

into three groups, for tyrosine, serine and threonine phosphorylations.

But that's not exactly how it works.

It turns out that serine and threonine are pretty much indistinguishable for kinases,

so the ones that can phosphorylate a serine can also hit a threonine.

Apart from serine/threonine kinases, you have the tyrosine kinases and there is an overlap,

which are called dual specificity kinases (even though triple specificity would�ve

made more sense, because they recognise all three phosphorylatable amino acids, but that�s

scientific nomenclature for you).

There's also a group of close to 50 kinases that have lost their phosphorylation activity

and we call those pseudokinases, although some pseudokinases have a bit of activity

left in certain circumstances.

When a protein gets phosphorylated, the phosphate on a serine, threonine or tyrosine residue

acts as a little flag to other proteins.

They're attracted to the phosphorylated protein where they weren't before, and they bind on

top of the phosphate.

So these phosphorylations are able to cause interactions between proteins and that way

signals can be passed on all the way across a cell.

Ultimately, this can lead to a variety of things to happen with the cell, like cell

division, cell migration and even cell death.

At the same time, faulty, hyperactived kinases can transmit too many phosphorylation

signals, and this can lead to diseases such as cancer.

So let's take a closer look at how a kinase can pinch off a phosphate and transfer it

across.

Here you see a structure of a kinase.

In the middle it has a big pocket that ATP can sit inside.

Even though there is a fair bit of variation in the amino

acid sequence between human kinases, a few amino acids are exactly the same in all of

them.

Let's have a look where they sit and what they do.

The important bits of a kinase can be split up into three groups:

1) the bits that bind ATP 2) the bits that bind the target substrate

3) the bits that transfer the phosphate across.

In order for ATP to stay inside the ATP binding pocket of a kinase, it needs a seat belt to

keep it in place and there are a few amino acids responsible for that.

Firstly, you've got the glycine-rich loop, which extends over the top of ATP.

Then there is a very important lysine residue that binds to the alpha and beta phosphates

of ATP, keeping it in place.

If you mutate these amino acids, the kinase won't be able to bind

ATP any more, and it loses its activity.

A conserved glutamate forms a salt bridge with that lysine, and that�s important for

keeping the shape of the kinase stable.

On the other side of the pocket there is the DFG motif, which binds metal ions that you

need to transfer the phosphate.

The DFG is also the start of a large loop, called the activation loop.

The amino acid sequence in the activation loop determines whether the kinases recognises

tyrosines or serines & threonines.

Lastly, there�s the YRD motif (or HRD in many kinases).

This last bit is maybe the most important.

You need one particular amino acid (the aspartate) in this motif to actually transfer the gamma

phosphate from ATP onto a substrate serine, threonine or tyrosine.

If you lose that aspartate, the kinase can still bind ATP, but it won't actually transfer

the phosphate.

So kinases are extremely important for the way cells transmit signals and regulate their

behaviour.

Next time we'll go into a bit more detail about some of the roles that kinases can have

in diseases such as cancer, and how we can target them with very specific drugs.

Thanks for watching, drop any questions you might have down in the comments below and

don't forget to hit the subscribe button.

See you next time.