Structure of MHC Proteins Flashcards
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Questions and Answers

What are the 2 types of MHC proteins?

  • MHC III
  • MHC II (correct)
  • MHC IV
  • MHC I (correct)

Peptides derived from cytosolic proteins are bound to what class of MHC proteins?

MHC I

What do MHC proteins present on their surface?

Present peptides

What are the 3 genes that encode class I MHC molecules?

<p>HLA-A, HLA-B, HLA-C</p> Signup and view all the answers

What properties allow MHC proteins to be diverse?

<p>Highly polymorphic, several hundred alleles</p> Signup and view all the answers

What is the structure of Class I MHC proteins?

<p>Two polypeptide chains, α chain and β2-microglobulin</p> Signup and view all the answers

Where do the sequence differences between the vast number of alleles mainly occur?

<p>In the peptide binding region</p> Signup and view all the answers

What are anchor residues crucial for?

<p>Binding</p> Signup and view all the answers

A tremendous range of peptides can be presented by MHC class I molecules because?

<p>Each variant requires a unique set of anchor residues</p> Signup and view all the answers

What is an additional feature of MHC-peptide complexes?

<p>Kinetic stability</p> Signup and view all the answers

The receptor that recognizes peptides displayed by MHC proteins on target cells is the?

<p>T-cell receptor (TCR)</p> Signup and view all the answers

Class II MHC proteins are expressed only by?

<p>Antigen-presenting cells</p> Signup and view all the answers

Where do the peptides presented by class II MHC proteins come from?

<p>Degradation of proteins internalized by endocytosis</p> Signup and view all the answers

What is the difference between MHC I and MHC II?

<p>MHC I has multiple genes encoding it; MHC II has two chains (α and β)</p> Signup and view all the answers

What is the structure of MHC II?

<p>Two chains α (33 kDa) and β (30 kDa)</p> Signup and view all the answers

What is the difference in structure between the 2 MHCs?

<p>MHC I has one α chain and one β2-microglobulin; MHC II has two chains α and β</p> Signup and view all the answers

Why can class II molecules accommodate longer peptides than class I?

<p>Peptide-binding site is open at both ends</p> Signup and view all the answers

Peptide-binding specificity of each class II molecule depends on?

<p>The binding pockets that recognize specific amino acids</p> Signup and view all the answers

Flashcards

MHC Polymorphism

MHC proteins are highly polymorphic, meaning they have many different versions (alleles) within a population. This diversity helps the immune system recognize a wide range of pathogens.

MHC Function

MHC proteins are responsible for presenting antigen fragments (peptides) to T cells, triggering an immune response.

MHC I Peptide Source

MHC class I proteins present peptides derived from proteins found inside cells (the cytosol).

MHC II Peptide Source

MHC class II proteins present peptides derived from proteins that have been taken up by cells via endocytosis.

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MHC Peptide Binding Region Variability

The region of MHC proteins where peptides bind is highly variable, contributing to the diverse range of peptides they can present.

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Anchor Residues

Anchor residues are specific amino acids within a peptide that bind to specific pockets on MHC proteins, ensuring stable peptide-MHC complex formation.

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MHC Peptide Presentation Specificity

Each MHC protein variant has specific anchor residue requirements, allowing diverse peptides to be presented.

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MHC-Peptide Complex Stability

MHC-peptide complexes are very stable, holding onto peptides for a prolonged time (days).

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TCR Recognition of MHC-Peptide Complexes

The T cell receptor (TCR) is a protein on T cells that specifically recognizes and binds to peptides displayed by MHC molecules.

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Genes Encoding MHC I

Class I MHC molecules are encoded by three genes: HLA-A, HLA-B, and HLA-C.

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Genes Encoding MHC II

Class II MHC molecules are encoded by multiple genes, including HLA-DR, HLA-DP, and HLA-DQ.

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MHC I Structure

MHC class I molecules consist of a single, heavier alpha chain and a smaller beta2-microglobulin chain.

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MHC II Structure

MHC class II molecules consist of two chains of similar size, an alpha chain and a beta chain.

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MHC Peptide Length Accommodation

Class II MHC molecules can accommodate longer peptides in their binding site, unlike class I, which prefers shorter peptides.

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Expression of MHC II

Class II MHC proteins are expressed primarily on antigen-presenting cells (APCs) such as B cells, macrophages, and dendritic cells.

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MHC II Specificity

The binding specificity of MHC II molecules is determined by pockets in its peptide-binding site, which recognize specific amino acids called anchor residues.

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Class I MHC Structure

Class I MHC molecules are composed of a heavier alpha chain and a lighter beta2-microglobulin chain.

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Class II MHC Structure

Class II MHC molecules consist of two chains of similar size: an alpha chain and a beta chain.

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Study Notes

Types of MHC Proteins

  • Two main classes: MHC I and MHC II.

Peptide Binding

  • MHC I binds peptides derived from cytosolic proteins.
  • MHC II presents peptides from proteins internalized via endocytosis.

Function of MHC Proteins

  • MHC proteins display peptides on their surface for recognition by T-cell receptors (TCR), facilitating immune response.

Genes Encoding MHC Molecules

  • Class I MHC molecules encoded by three genes: HLA-A, HLA-B, HLA-C (Human leukocyte antigen).

Diversity of MHC Proteins

  • MHC proteins are highly polymorphic with hundreds of alleles for each class, contributing to their diversity.

Structure of Class I MHC

  • Composed of two polypeptide chains: the larger α chain and the smaller β2-microglobulin.

Sequence Variability

  • Most sequence differences in MHC alleles occur in the peptide binding region.

Importance of Anchor Residues

  • Anchor residues are essential for stable peptide binding to MHC proteins.

Peptide Presentation Versatility

  • Each MHC I variant requires unique anchor residues, allowing presentation of a vast range of peptides.

Stability of MHC-Peptide Complexes

  • MHC-peptide complexes exhibit high kinetic stability, retaining peptides for days.

Recognition of Peptide-MHC Complexes

  • The T-cell receptor (TCR) specifically recognizes peptides displayed by MHC molecules.

Expression of MHC II

  • Class II MHC proteins are expressed solely by antigen-presenting cells, including B cells, macrophages, and dendritic cells.

Source of Peptides for MHC II

  • Peptides for MHC II arise from degradation of internalized proteins, not from cytosolic sources.

Differences between MHC I and MHC II

  • MHC II is encoded by multiple genes (HLA-DR, HLA-DP, HLA-DQ); consists of two chains (α and β), unlike MHC I which has a single heavy chain and β2-microglobulin.

Structure of MHC II

  • MHC II consists of α (33 kDa) and β (30 kDa) chains; their peptide-binding site is formed by contributions from both chains.

Structural Differences between MHC Classes

  • Class I MHC has one heavy chain and light chain (β2-microglobulin). Class II MHC has two chains of similar size.

Peptide Length Accommodation

  • Class II can accommodate longer peptides due to an open peptide-binding site at both ends.

Specificity of Class II Binding

  • The binding specificity of class II molecules is defined by pockets that recognize specific amino acids (anchor residues) at particular positions.

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Description

This quiz covers the fundamentals of MHC proteins, including their types and functions. It focuses on the roles of MHC I and MHC II in presenting peptides to T-cell receptors. Ideal for students studying immunology or related topics.

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