Name: allosteric changes in protein shape
Uploaded: 2023-04-30T18:28:43.000Z
Duration: 1 min 58 s
Channel: JoVE

K12 Standards

Next Generation Science Standards

High School

Life Science

from-molecules-to-organisms-structures-and-processes

From Molecules to Organisms: Structures and Processes

HS-LS1-1

Cooperative Allosteric Transitions

לחלבונים רבים יש תת-יחידות מרובות, כאשר כל תת-יחידה מכילה אתר קישור ליגנד נפרד.
כאשר מולקולה, המכונה אפנן, נקשרת לאחת מתתי-היחידות היא גורמת לשינוי קונפורמטיבי באתרי הקישור של תת-היחידות האחרות, תוך שינוי זיקתן לליגנדות המתאימות. זה נקרא מעבר אלוסטרי שיתופי וניתן להסביר אותו על ידי מספר מודלים תיאורטיים.
המודל המתואם או "הכל או אף אחד" מניח שכל יחידות המשנה קיימות יחד בקונפורמציה "כבויה" או "מופעלת".
קשירה יכולה להתרחש בכל אחת מהצורות, עם זאת, למצב "מופעל" יש זיקה גבוהה יותר לליגנד מאשר למצב "כבוי". כאשר ליגנד נקשר באחת מתתי-היחידות, הוא מקדם טרנספורמציה סימולטנית של כל אתרי הקישור לצורת הזיקה הגבוהה.
קואופרטיביות יכולה להיות מוסברת גם על ידי המודל הרציף, המניח שכל תת-יחידה יכולה להתקיים באופן עצמאי במצב זיקה גבוהה או נמוכה, אך סביר יותר שתהיה במצב זיקה גבוהה כאשר הליגנד קשור לכל אחת מתתי-היחידות. 
אתרי הקישור של חלבונים אלוסטריים הם בדרך כלל תערובת של מקטעים גמישים וקבועים של שרשרת חומצות האמינו. כאשר ליגנד נקשר, חלקים בלתי יציבים אלה מתייצבים בקונפורמציה מסוימת, וזה משפיע על צורת אתרי הקישור על יחידות המשנה האחרות. 
המוגלובין הוא דוגמה לחלבון טטרמרי שעובר מעבר אלוסטרי שיתופי כאשר חמצן נקשר.
לכל תת-יחידה של המוגלובין יש אתר קשירה יחיד. כאשר מולקולה אחת של חמצן נקשרת לתת-יחידה אחת, הקואופרטיביות מגבירה את הזיקה לחמצן באתרי הקישור הנותרים, מה שמקל על חמצן להיקשר למולקולת המוגלובין שכבר יש חמצן קשור אליה.

<ol>
	<li>קורניש-באודן, א. (2014), הבנת אינטראקציות אלוסטריות ושיתופיות באנזימים. פברואר J, 281: 621-632. doi:10.1111/פברואר.12469</li>
	<li>אלברטס ואחרים, מהדורה שישית; עמודים 152-153</li>
	<li>עקרונות לנינגר בביוכימיה, מהדורה חמישית, עמודים 162,165</li>
</ol>

מעברים אלוסטריים שיתופיים

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מעברים אלוסטריים שיתופיים יכולים להתרחש בחלבונים מולטימריים, כאשר לכל תת-יחידה של החלבון יש אתר קושר ליגנד משלה. כאשר ליגנד נקשר לכל אחת מתת-היחידות הללו, הוא מעורר שינוי קונפורמציה המשפיע על אתרי הקישור ביחידות המשנה האחרות; זה יכול לשנות את הזיקה של האתרים האחרים לליגנדים שלהם. היכולת של החלבון לשנות את צורת אתר הקישור שלו מיוחסת לנוכחות של תערובת של מקטעים גמישים ויציבים במבנה. מולקולה שמפעילה את השינוי הזה ידועה כאפנן.

שני מודלים משמשים לעתים קרובות כדי להסביר שיתופיות בחלבונים מולטימריים: המודל המתואם והמודל הרציף. המודל המרוכז, הידוע גם כמודל הכל-או-אף אחד, משער שכל תת-היחידות של חלבון מולטימרי עוברות בו-זמנית בין הקונפורמציות "מופעל" ו"כבוי". בצורת "מופעל", לאתרי הקישור יש זיקה גבוהה לליגנדים שלהם, ובצורה "כבויה", לאתרי הקישור יש זיקה נמוכה. כאשר ליגנד נקשר לכל אחת מיחידות המשנה, הוא מקדם את ההמרה לצורת הזיקה הגבוהה, ובמקביל משנה את הקונפורמציה של כל אתרי הקישור האחרים של החלבון. למרות שליגנד יכול להיקשר לכל אחת מהצורות, קל לו יותר להיקשר כאשר הוא נמצא בצורה בעלת זיקה גבוהה.

המודל הרציף מניח שכל תת-יחידה של חלבון מולטימרי יכולה להתקיים באופן עצמאי בקונפורמציה "מופעלת" או "כבויה", כלומר בצורת זיקה נמוכה או גבוהה, ללא קשר למצבן של תת-היחידות האחרות. קישור של ליגנד לתת-יחידה משנה את שיווי המשקל בין צורות הזיקה הנמוכה והגבוהה כך שסביר יותר שתת-היחידה תהיה בצורת זיקה גבוהה. בנוסף, ליגנד המקשר על תת-יחידה אחת משנה את שיווי המשקל עבור תת-היחידות האחרות בחלבון. זה מגדיל את הסבירות שברגע שליגנד אחד נקשר, ליגנד אחר ייקשר לתת-יחידה אחרת. שיתוף פעולה זה מגביר את רגישות החלבון לריכוז ליגנד. קישור ליגנד באתר בודד יכול לשנות את הזיקה על כל מולקולת החלבון, ובכך לאפשר תגובה מהירה בריכוזים נמוכים.

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מעברים אלוסטריים שיתופיים יכולים להתרחש בחלבונים מולטימריים, כאשר לכל תת-יחידה של החלבון יש אתר קשירת ליגנד משלה. כאשר ליגנד ...

Education

JoVE Core

Cell Biology

ביולוגיה של התא

Unit 1

יחידה 1

Protein Function

תפקוד חלבונים

KEY TERMS AND CONCEPTS

מונחים ומושגים מרכזיים

allosteric changes in protein shape

Allosteric changes in protein shape help explain how some proteins switch between active and inactive states. These transitions are cooperative, which means a change in one part of the protein can affect other parts of the same molecule.

The video focuses on how these shifts in shape support protein function. It also shows that allosteric transitions can be described with different models. In the concerted model, the protein changes shape as a whole. In the sequential model, the change happens step by step across the protein.

These models help students understand how proteins respond to signals in the cell. They also show why protein shape is closely linked to biological activity.

Allosteric Changes in Protein Shape

ligand binding sites

Ligand Binding Sites in Proteins

Ligand binding sites are specific parts of a protein where a ligand can attach. A ligand is a molecule that binds to another molecule, often to help start or change a biological process. These sites matter because the shape and chemistry of the protein help determine which ligands can fit and bind. Proteins do not bind every ligand in the same way. The binding site provides a matching surface that supports a close interaction. In many cases, this interaction is important for how cells respond...

protein-protein interfaces

Protein Binding Surfaces and Contacts

Protein binding surfaces and contacts help proteins recognize and attach to each other. These interfaces are the regions where two proteins meet and interact. They are important for many cell processes and for how proteins work together. A protein-protein interface is not just a random touch point. It is shaped by the three-dimensional form of each protein. The matching surfaces allow a stable interaction to form when the proteins fit together well. Studying these interfaces helps explain how...

conserved binding sites

Conserved Binding Sites in Protein Families

Conserved binding sites are regions on proteins that stay similar across related proteins. These shared areas often help proteins interact with the same molecules. For this reason, they are useful clues when comparing protein families. A conserved site can help identify where a protein binds. It can also show which parts of the protein are important for function. When the same pattern appears in several proteins, it suggests that the site has been kept through evolution. Scientists look at...

cofactors and coenzymes

Enzyme Helpers: Metals and Vitamins

Enzyme helpers include cofactors and coenzymes. Enzymes are proteins made of amino acids, and the functional groups on those amino acids can drive many chemical reactions through ionic interactions or acid-base reactions. But amino acids alone cannot handle oxidation-reduction and group transfer reactions, so they need non-protein helpers called cofactors. Cofactors are often described as the chemical teeth of an enzyme. They can be metal ions or organic molecules called coenzymes. These...

cooperative allosteric transitions

Allosteric changes in protein shape help explain how some proteins switch between active and inactive states. These transitions are cooperative, which means a change in one part of the protein can affect other parts of the same molecule. The video focuses on how these shifts in shape support protein function. It also shows that allosteric transitions can be described with different models. In the concerted model, the protein changes shape as a whole. In the sequential model, the change happens...

protein kinases and phosphatases

Protein Kinases and Phosphatases in Cell Control

Protein kinases and phosphatases help control how proteins work in cells. Kinases add phosphate groups to proteins. Phosphatases remove those phosphate groups. This phosphorylation and dephosphorylation process can change a protein’s shape and activity. It is one way cells turn protein function on or off at the right time. These changes also help cells respond to signals and manage many cell activities. Together, protein kinases and phosphatases keep cellular signaling balanced. When one adds...

gtpases and their regulation

GTPase Molecular Switches and Control

GTPases are molecular switches that help control cell activity. They bind guanosine triphosphate, or GTP, and can change between active and inactive states. This switch-like behavior makes them important in many cell processes. The protein is active when GTP is bound and inactive when guanosine diphosphate, or GDP, is bound. GTPases can also turn themselves off by breaking down GTP into GDP. This built-in control helps cells regulate when the protein is on or off. Their activity is regulated...

covalently linked protein regulators

Protein Regulation by Covalent Bonds

Protein regulation by covalent bonds helps control how cells respond to changing conditions. A covalent bond is a strong chemical link, and in this context it can change how a protein behaves. Some regulators work by attaching a chemical group directly to a protein. This covalent change can alter the protein's activity, its location in the cell, or how long it stays active. Because the change is built into the protein itself, it can have a strong effect on cell function. Covalently linked...

protein complexes with interchangeable parts

protein-complexes-with-interchangeable-parts

Modular Protein Complexes in Cells

Protein complexes in cells can be built from interchangeable parts. This modular design lets some complexes share common subunits while still changing their behavior. A well-known example is the ubiquitin ligase complex called SCF. SCF stands for Skp1-Cullin-F-box, and it helps attach ubiquitin, a small protein tag, to target proteins. The core of SCF stays the same, but the F-box protein can change. The interchangeable F-box subunit gives the complex its specificity. Different F-box proteins...

mechanical protein function

Proteins That Generate Cell Movement

Mechanical proteins help cells and tissues move. They turn chemical energy into force and motion. This process is important in many biological systems. These proteins are also called motor proteins. They interact with cell structures and can produce directed movement. In muscle cells, they support contraction. In other cells, they help with transport and shape changes. Mechanical protein function is a key part of how living systems work. It links protein activity to movement at the cellular...

structural protein function

Structural Proteins in Cells and Tissues

Structural proteins help cells and tissues keep their shape and strength. They are an important part of living systems because they provide support where it is needed most. Many structural proteins form fibers or other sturdy forms that resist stretching and wear. These proteins work as building materials in the body and help keep structures stable over time. Examples of structural proteins include collagen, actin, myosin, and keratin. Each one supports a different part of the body, but all...

protein networks

Mapping Protein Interaction Networks

Protein interaction networks show how proteins work together inside a cell. These networks help scientists see which proteins connect with each other and how those links support cell activity. Researchers often use online tools to build and study these networks. The transcript points to IntAct and STRING as examples of resources that can help predict and organize protein interactions. These tools make it easier to compare protein links and look for patterns in the network. Protein networks...

key terms and concepts

Explore cooperative allosteric transitions and learn how protein shape changes can switch proteins between active and inactive states using concerted and sequential models.

Allosteric Changes in Protein Shape | JoVE K12

cell biology

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Protein Folding

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Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins, which carry out the essential functions of life through systems of specialized cells. [Assessment Boundary: Assessment does not include identification of specific cell or tissue types, whole body systems, specific protein structures and functions, or the biochemistry of protein synthesis.]

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Homeostasis
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Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms. [Clarification Statement: Emphasis is on functions at the organism system level such as nutrient uptake, water delivery, and organism movement in response to neural stimuli. An example of an interacting system could be an artery depending on the proper function of elastic tissue and smooth muscle to regulate and deliver the proper amount of blood within the circulatory system.] [Assessment Boundary: Assessment does not include interactions and functions at the molecular or chemical reaction level.]

HS-LS1-2

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Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis. [Clarification Statement: Examples of investigations could include heart rate response to exercise, stomate response to moisture and temperature, and root development in response to water levels.] [Assessment Boundary: Assessment does not include the cellular processes involved in the feedback mechanism.]

HS-LS1-3

Allosteric Changes in Protein Shape

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