Name: how amino acid sequence shapes proteins
Uploaded: 2023-04-30T10:34:15.000Z
Duration: 1 min 25 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

Protein Folding

Dans un peptide nouvellement synthétisé, les interactions entre ses acides aminés constitutifs guident son repliement en une structure tridimensionnelle stable appelée conformation native, souvent sa forme fonctionnelle.
Tout d’abord, la chaîne polypeptidique linéaire se replie en hélices alpha et en feuillets bêta par liaison hydrogène entre les résidus d’acides aminés.
Des chaînes latérales hydrophobes dépassant des hélices ou des feuillets bêta se rejoignent, éliminant les molécules d’eau environnantes. En conséquence, le polypeptide est emballé dans un intermédiaire faiblement plié avec un noyau hydrophobe.
Les résidus polaires à la surface forment des liaisons hydrogène et des interactions ioniques supplémentaires, tandis que les cystéines adjacentes forment des liaisons disulfure covalentes pour stabiliser la protéine dans sa conformation native.
Pour les protéines à plusieurs cystéines, l’enzyme disulfure isomérase catalyse l’échange rapide de groupes thiols, permettant une formation correcte de liaisons disulfure.
La plupart des protéines ne se replient pas d’elles-mêmes et sont aidées par les protéines de choc thermique et les chaperonines.
Ces chaperons moléculaires accélèrent le processus de repliement en liant le peptide déplié et en empêchant l’agrégation ou en fournissant un microenvironnement où le peptide peut se replier dans sa conformation native.

<ol>
	<li>Lodish, Harvey, et al. Biologie cellulaire moléculaire. 8e éd. W.H. Freeman and Company, 2016. Pages 81 à 85</li>
	<li>Donald Voet et Judith G Voet Biochimie. 4e éd. JOHN WILEY & SONS, INC. 2011. Pages 278 à 290</li>
	<li>Nelson et Cox, Lehninger, Principes de biochimie, 7e éd. W.H. Freeman and Company, 2016. Pages 396 à 407</li>
</ol>

repliement des protéines

Les protéines sont des chaînes d'acides aminés liées entre elles par des liaisons peptidiques. Lors de la synthèse, une protéine se plie selon une conformation tridimensionnelle, essentielle à sa fonction biologique. Les interactions entre ses acides aminés constitutifs guident le repliement des protéines et, par conséquent, la structure de la protéine dépend principalement de sa séquence d'acides aminés.

La Structure des Protéines est Essentielle à sa Fonction Biologique

Les protéines remplissent un large éventail de fonctions biologiques telles que la catalyse de réactions chimiques, la défense immunologique, le stockage, le transport, la communication cellulaire, le mouvement et le soutien structurel. La fonction d'une protéine dépend principalement de la reconnaissance et de la liaison d'autres molécules, à l'instar d'une serrure et d'une clé. L’activité spécifique de chaque protéine dépend donc de son architecture tridimensionnelle unique.

Pour qu’une protéine soit fonctionnelle, elle doit se replier avec précision. La plupart des protéines passent par plusieurs formes intermédiaires avant de se replier dans la structure biologiquement active la plus stable. Un mauvais repliement des protéines peut altérer le fonctionnement global de la cellule. L'accumulation de protéines mal repliées ou dépliées chez l'homme conduit à la mucoviscidose, à la maladie d'Alzheimer, à la maladie de Parkinson, à la sclérose latérale amyotrophique et à la maladie de Creutzfeldt-Jakob.

Déterminants Critiques de la Structure des Protéines

Les protéines sont constituées d’une ou plusieurs chaînes d’acides aminés appelées polypeptides. Un polypeptide est synthétisé sous la forme d’une chaîne linéaire qui se replie rapidement sur elle-même pour former une structure tridimensionnelle. Les termes polypeptide et protéine sont parfois utilisés de manière interchangeable, mais le plus souvent, un polypeptide replié capable de remplir une fonction biologique est appelé protéine. Une structure protéique est généralement décrite à quatre niveaux : primaire, secondaire, tertiaire et quaternaire. La plupart des polypeptides se replient en une structure tertiaire globalement compacte et globulaire, telle que l'hémoglobine, la protéine transportant l'oxygène dans le sang. Certaines protéines comme les kératines forment de longues fibres et se trouvent couramment dans les cheveux et les ongles. Les protéines globulaires sont solubles dans l’eau, contrairement aux protéines fibreuses.

La séquence d'acides aminés dans la chaîne polypeptidique est le principal déterminant de sa structure. La séquence d'acides aminés détermine le type et l'emplacement des structures secondaires. De plus, la structure tertiaire globale d’une protéine est principalement stabilisée par des liaisons chimiques entre les chaînes latérales des acides aminés, les groupes chimiques uniques qui distinguent les acides aminés les uns des autres. Ces chaînes latérales sont soit chargées (positivement ou négativement), polaires non chargées ou non polaires.

Les acides aminés ont des caractéristiques physiques et chimiques uniques en fonction de leurs groupes latéraux. Par exemple, les acides aminés polaires et chargés interagissent avec l’eau pour former des liaisons hydrogène et sont appelés hydrophiles. En revanche, les acides aminés non polaires évitent les interactions avec l’eau et sont dits hydrophobes. Ainsi, lorsqu’une protéine est repliée dans un environnement cellulaire, les chaînes latérales d’acides aminés hydrophobes sont enfouies au cœur de la protéine, loin du milieu aqueux. En revanche, les chaînes latérales des acides aminés hydrophiles sont exposées à la surface de la protéine.

Les acides aminés hydrophobes étroitement emballés dans le noyau protéique conduisent à la formation de faibles interactions de Van der Waals entre les groupes de chaînes latérales. Ces forces de Van der Waals confèrent une stabilité supplémentaire à la protéine repliée. Les acides aminés polaires exposés à la surface de la protéine sont libres de former des liaisons hydrogène avec des molécules d'eau ou d'autres chaînes latérales d'acides aminés polaires. Les acides aminés chargés positivement et négativement sont également présents à l’extérieur d’une protéine, où ils forment des liaisons ioniques avec d’autres acides aminés proches de charges opposées.

Des liaisons disulfure se forment entre deux groupes sulfhydryles, ou SH, sur l'acide aminé cystéine. Il s’agit d’une interaction robuste qui agit comme un renforcement de la protéine repliée. Les liaisons disulfure verrouillent la protéine repliée dans sa conformation tridimensionnelle la plus favorisée. Le bon repliement d'une protéine dépend également d'autres facteurs de l'environnement cellulaire comme le pH, la concentration en sel, la température, etc. La modification des conditions physiques et chimiques dans un environnement protéique affecte les interactions chimiques qui maintiennent la protéine ensemble et peut provoquer un mauvais repliement de la protéine. ou se déplier et perdre sa fonction biologique – un processus connu sous le nom de dénaturation des protéines.

Repliement des Protéines

Les protéines sont des chaînes d’acides aminés reliées entre elles par des liaisons peptidiques. Lors de la synthèse, une protéine se replie dans une conformation tridimensionnelle, essentielle à ...

Education

Enseignement

JoVE Core

Cell Biology

Biologie cellulaire

Unit 1

Unité 1

Protein Structure

Structure des protéines

KEY TERMS AND CONCEPTS

TERMES ET CONCEPTS CLÉS

how amino acid sequence shapes proteins

Proteins get their shape from the order of amino acids in a polypeptide chain. After a protein is made, the chain folds into a three-dimensional form that is needed for it to work. The way amino acids interact with one another guides this folding.

Protein structure matters because proteins do many jobs in cells. They can speed up chemical reactions, help with immune defense, store materials, carry substances, send cell signals, support movement, and provide structure. A protein usually works by binding to another molecule, much like a lock and key. That is why its specific three-dimensional shape is so important.

To be functional, a protein must fold correctly. Many proteins pass through several intermediate forms before reaching the most stable and biologically active shape. When proteins misfold, they can disrupt cell function. In humans, misfolded or unfolded proteins are linked with cystic fibrosis, Alzheimer’s disease, Parkinson’s disease, amyotrophic lateral sclerosis, and Creutzfeldt-Jakob disease.

Proteins are made of one or more amino acid chains called polypeptides. A polypeptide starts as a linear chain and then folds quickly into a three-dimensional structure. The words polypeptide and protein are sometimes used interchangeably, but a folded polypeptide that can do a job is usually called a protein. Protein structure is often described at four levels: primary, secondary, tertiary, and quaternary.

Most polypeptides fold into a compact, globular tertiary structure. Hemoglobin, the oxygen-carrying protein in blood, is an example. Some proteins, such as keratins, form long fibers and are found in hair and nails. Globular proteins are usually soluble in water, while fibrous proteins are not.

The amino acid sequence is the main factor that determines protein shape. It helps decide where secondary structures form and how the full tertiary structure develops. Side chains, the chemical groups that make amino acids different from one another, stabilize the folded protein. These side chains may be charged, polar but uncharged, or non-polar.

Polar and charged amino acids interact with water and are called hydrophilic. Non-polar amino acids avoid water and are called hydrophobic. When a protein folds in a cell, hydrophobic side chains are usually buried in the core, away from water, while hydrophilic side chains stay on the surface. Tight packing in the hydrophobic core creates weak Van der Waals interactions that help stabilize the structure.

Hydrophilic side chains on the outside can form hydrogen bonds with water or with other polar side chains. Positively and negatively charged amino acids can also form ionic bonds with nearby oppositely charged amino acids. Another strong bond, called a disulfide bond, forms between two sulfhydryl, or SH, groups on cysteine. This bond helps lock the protein into its most stable three-dimensional shape.

Protein folding also depends on the cell’s environment. pH, salt concentration, and temperature can affect the chemical interactions that hold a protein together. If these conditions change, a protein may misfold or unfold and lose its function. This process is called protein denaturation.

How Amino Acid Sequence Shapes Proteins

what are proteins?

Protein Building Blocks and Folding

Proteins are built from amino acids linked by peptide bonds. Long chains of amino acids are often called polypeptides, and the terms proteins and polypeptides are sometimes used the same way. In this context, polypeptides with a molecular weight below 10,000 daltons are called polypeptides, while proteins have a higher molecular weight. Very short chains with fewer than 20 amino acids are called peptides or oligopeptides. Amino acids are the basic units of proteins. Each amino acid has a...

protein organization

Protein Folding Levels and Bonds

Proteins are built from amino acids and folded into shapes that support many cell jobs. They help with DNA replication, molecular transport, catalysis, and structural support. Their function depends on how their amino acids are arranged and folded. Protein structure is organized in levels. The primary structure is the amino acid sequence in a polypeptide chain. Amino acids are joined by peptide bonds, and the chain has two ends: the amino terminus, or N-terminus, and the carboxyl terminus, or...

protein folding

Proteins get their shape from the order of amino acids in a polypeptide chain. After a protein is made, the chain folds into a three-dimensional form that is needed for it to work. The way amino acids interact with one another guides this folding. Protein structure matters because proteins do many jobs in cells. They can speed up chemical reactions, help with immune defense, store materials, carry substances, send cell signals, support movement, and provide structure. A protein usually works...

protein families

Protein Families and Superfamilies

Protein families and superfamilies group proteins with shared features. These groups help scientists organize proteins by common structure, function, or evolutionary history. The classification can show how related proteins are connected across different organisms. A protein family usually includes proteins that are closely related. A superfamily is a broader group that can include several families with more distant relationships. These categories help explain why some proteins share similar...

conservation of protein domains

Protein Domains Shared Across Proteins

Protein domains are shared structural and functional parts of proteins. A domain is a region that can often be found in more than one protein, even when the full proteins are different. This conservation means that a protein domain may keep a similar shape or role across related proteins. Because of that, scientists can compare proteins by looking for domains that stay the same. Conserved domains help reveal how proteins are related and how they may work. The topic of protein domain...

globular and fibrous proteins

Protein Shapes: Globular vs Fibrous

Proteins can have globular or fibrous shapes, and these shapes help explain how they work in the body. Globular proteins are compact and usually fold into rounded forms. Fibrous proteins are long, extended molecules that often provide support and structure. The shape of a protein is tied to its function. Globular proteins often take part in chemical jobs in cells, while fibrous proteins are better suited for strength and stability. These structural differences make the two groups easy to...

intrinsically disordered proteins

Flexible Protein Regions and Disorder

Intrinsically disordered proteins have flexible regions that do not settle into one fixed shape. Instead, these proteins can remain dynamic and change form as they move through the cell. This flexibility is an important part of their structure and function. Many proteins need a stable folded shape to work properly. Intrinsically disordered proteins are different because they may lack a single rigid structure under normal conditions. Their shifting shape can help them take part in cell...

protein complex assembly

Protein Complex Formation and Function

Protein complex formation explains how proteins join together to carry out specific jobs in cells. These groups are called protein complexes, and they can form in more than one way. Some complexes are homomeric, which means they contain the same kind of protein subunit. Others are heteromeric, which means they contain different protein subunits. The assembly process helps show how protein shape and subunit choice affect function. When proteins combine, the resulting complex can behave...

conjugated proteins

Conjugated Proteins and Their Bound Groups

Conjugated proteins are proteins that include a nonprotein part called a prosthetic group. This added group helps give the protein its full structure or function. The video explains how the protein part and the bound group work together. Several common types of conjugated proteins are named by the kind of group attached. Nucleoproteins contain nucleic acids. Glycoproteins contain carbohydrate groups, and lipoproteins contain lipid groups. Other examples include phosphoproteins, which have...

amyloid fibrils

Amyloid Fibrils and Protein Aggregation

Amyloid fibrils are protein aggregates with a very specific structure. They are made when proteins misfold and stick together in long, ordered fibers. This structure makes them different from many other protein clumps. Amyloid fibrils are important in biology because they are linked to protein aggregation. Protein aggregation means proteins build up into groups instead of staying properly folded and separate. In many cases, this process is associated with disease and abnormal cell function. <br...

key terms and concepts

Learn how amino acid sequence, side-chain interactions, and cell conditions shape protein structure, stability, and function in high school biology.

How Amino Acid Sequence Shapes Proteins | JoVE K12

cell biology

JoVE Core Biologie cellulaire illustre les processus cellulaires complexes dans des leçons vidéos complètes mais faciles à comprendre. Cette collection se concentre sur les composants et fonctions essentiels de la cellule ; cela inclut les organelles et les membranes ainsi que le transport et le métabolisme énergétique cellulaire. Elle est complétée par nos vidéos de scientifiques à l'action qui démontrent l'application de la biologie cellulaire dans des expériences concrètes.

new-york-state-science-learning-standards

New York State Science Learning Standards

Structure and Function

HS-LS1-1.

Characteristics of Life

Biology is a natural science that studies life and living organisms, including their structure, function, development, interactions, evolution, ...

https://cloudfront.jove.com/files/media/science-education/science-education-thumbs/10647.jpg

Cell Structure

Background
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Cytoplasm

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The Nucleus

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The Central Dogma

The DNA Helix

Nucleic Acids

DNA as a Genetic Template

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Chromosome Structure

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RNA Structure

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Types of RNA

Three main types of RNA are involved in protein synthesis: messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA). These RNAs perform diverse ...

Conservation of Protein Domains

Transcription

Transcription is the synthesis of RNA from a DNA sequence by RNA polymerase. It is the first step in producing a protein from a gene sequence. ...

Globular and Fibrous Proteins

Translation

Translation is the process of synthesizing proteins from the genetic information carried by messenger RNA (mRNA). Following transcription, it constitutes ...

Intrinsically Disordered Proteins

Ribosomes

Ribosomes translate genetic information encoded by messenger RNA (mRNA) into proteins. Both prokaryotic and eukaryotic cells have ribosomes. Cells that ...

Protein Complex Assembly

Protein and Protein Structures

Conjugated Proteins

Proteins: From Genes to Degradation

Amyloid Fibrils

What are Proteins?

Proteins are polymers of amino acids linked together by peptide bonds. Proteins and polypeptides are interchangeably used to refer to long chains of amino ...

Ligand Binding Sites

Protein Organization

Proteins are polymers of amino acid residues. They are versatile and responsible for different cellular functions, including DNA replication, molecular ...

Protein-Protein Interfaces

Proteins are chains of amino acids linked together by peptide bonds. Upon synthesis, a protein folds into a three-dimensional conformation, critical to ...

Conserved Binding Sites

Cofactors and Coenzymes

Enzymes are proteins made of amino acids. The functional group of each constituent amino acid catalyzes a wide variety of chemical reactions via ionic ...

Cooperative Allosteric Transitions

Protein Kinases and Phosphatases

GTPases and their Regulation

Covalently Linked Protein Regulators

protein-complexes-with-interchangeable-parts

Protein Complexes with Interchangeable Parts

Mechanical Protein Function

Structural Protein Function

Protein Networks

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.]

Levels of Organization

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Animal and Plant Cell Structure

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structural-organization-of-the-human-body-an-overview

Structural Organization of the Human Body: An Overview

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Overview of Human Digestion

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Anatomy of the Intestines

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Accessory Organs

Accessory organs are those that participate in the digestion of food but do not come into direct contact with it like the mouth, stomach, or intestine do. ...

Lipid Digestion

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Protein Digestion

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Carbohydrate Digestion

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What is a Nervous System?

Overview

The nervous system is the collection of specialized cells responsible for maintaining an organism&rsquo;s internal environment and coordinating ...

The Parasympathetic Nervous System

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The Sympathetic Nervous System

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Oogenesis

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Fertilization

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an-introduction-to-the-zebrafish-danio-rerio

An Introduction to the Zebrafish: Danio rerio

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Physiology of the Circulatory System

Homeostasis
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Measuring Blood Pressure
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Anatomy of the Heart

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Measuring Circulatory System Function in Humans
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Blood Flow

Blood is pumped by the heart into the aorta, the largest artery in the body, and then into increasingly smaller arteries, arterioles, and capillaries. The ...

What Are Osmoregulation and Excretion?

Organisms must keep bodily fluids at a constant temperature and pH while maintaining specific solute concentrations in order to support life functions. ...

Blood Withdrawal I

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Kidney Structure

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Blood Withdrawal II

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What is the Immune System?

Overview

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Bone Remodeling

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Spermatogenesis

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Bone Structure

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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

What is Homeostasis?

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Negative and Positive Feedback

Homeostatic Imbalance

Homeostasis is the maintenance of a stable internal environment within the body, which is crucial for the proper functioning of cells, tissues, organs, ...

pH Homeostasis

Acid-base homeostasis is essential for maintaining normal physiological activities in humans. The pH of various body fluids is strictly regulated because ...

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

How Amino Acid Sequence Shapes Proteins

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