Protein Structure Flashcards by Brooke Thornburg

Protein Structure

amino acids and polypeptide chain

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Polypeptide chain

peptide bond and phi, psi conformation

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Monoclonal

-produced from single B-lymphocyte clone and bind same epitope

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monoclonal antibodies (mAbs)

-used in research and therapy
-treat cancer, inflammatory disease, infectious and cardiovascular disease
-rapidly growing in use

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OKT3

-first therapeutic mAb approved
-targets CD3 on T cells
-depletes T cells
-immunosuppressor in preventing transplant rejection

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IgG antibody chains

-heavy and light (2 of each)
-constant or variable

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Light chain

VL CL

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Heavy chain

Vh3Ch

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Ig domains

-Ig fold packed with hydrophobic residues (keep folded and stable)
-110-amino acids
-sandwich of 2 antiparallel sheets linked by disulfide bonds

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Ig Fragments

-2 Fab regions
-Fc region

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Fc region

-stem of Ig
-binds Fc receptors
-activates complement-mediated cytotoxicity

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Full IgG antibody

-2 light chains with one VL and one CL
-2 heavy chains with one Vh and 3 CH’s
-2 copies of 2 chains
-Ig fold domain
-saccharide component

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Where does the hydrolysis producing Fab and Fc occur?

Hinge peptide (in the middle)

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saccharide component

in the constant H domains

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IgG flexibility

-due to loops between Ig domains
-Fab and Fc orientation varies among Ig molecules

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Protein function

dependent on binding and recognition

molecular recognition

-highly specific
-complementarity
-noncovalent interactions

Induced-fit

-structural changes occuring to enhance specificty and complementarity

Variable domains

-comprised of 3 hypervariable loops

Hypervariable loops

-comprised by variable domains
-vary in length and sequence in IgGs
-H and L chains (pic) (fab region)
-exact match between antigen and loops

Loop matching antigen

-high affinity
-induced fit
-specificity

Therapeutic Antibody mechanisms

-targeting extracellular ligand-receptor interactions
-antigen binding affinity is key

Ligand-receptor interactions

-bind to ligand or receptor (blockade)
-can lead to receptor down regulation

Human IgA monoclonal antibody

-blocks SARS-CoV-2 spike protein interaction with human ACE2 receptor
-forms MAb363 SARS-CoV-2 RBD complex

Monoclonal IgG molecules effectively recognize one antigen with high affinity because

the sequences of the hypervariable loops are selected to exquisitely complement the 3D shape of the antigen.

Antigens are recognized with high affinity by antibodies because

the sequences of three hypervariable loops are selected in an immune response to exquisitely complement the 3D shape of the antigen.

The assigned reading "Therapeutic monoclonal antibodies," describes several types of engineered antibody molecules that have been developed for therapeutics. Which of the names below does NOT refer to a type of therapeutic monoclonal antibody? Fab Fc BiTE® scFv

Twelve domains compose an IgG molecule. Of these domains,

all have two or more cysteine residues.

Disulfide Bridge

bond between light and heavy chains of Fab

Protease

-cleaves backbone -pepsin

pepsin

-protease -cleaves hinge peptide =2 Fab + Fc

How many IgG domains

-12 domains -4 variable (1 light, 1 heavy) x2 -8 constant (3 heavy, 1 light)x2

Acidic Residues

aspartic (R), glutamic (E)

Basic residues

lyseine and arginine

receptor blockade

-antibody binds to receptor -ligand cannot bind to receptor -could lead to endocytosis and removal of cell