Globular Proteins Fibrous Proteins Post-translational modifications of proteins (Lec 5)

Antibodies: Immunoglobulin G

Structure is amino terminals, the carboxy terminal, and dissulfide brides

• antibodies are important because they are a part of our immune system

• the dissulfide bonds holds the heavy and light chains together

  • hinge regions allow for the protein to be flexible to move the arm chains around and angle the protein to allow for binding with antigen

Antibodies are composed of two heavy chains & two light chains

• both are binded to the antigen (the molecule the the body recognizes)

In the antigen binding side there is an epitope

• the function of the anitbody’s variable regions is to recognize epitodes in an antigen

  

Antibodies are used in a lot of biochemical analysis

Hinge region: allows rotation around the polupeptide so that the molecule can bind to the antigen

• it purpose is basically flexbibility

  

Noncovalent interacitons btwn an antibody and its antigen

All are govern by the non covalent interactions (electrostatic forces, H bonds, ven der waals forces, hydrophobic forces, calton-pi interaciton)

• the noncovalent interactions govern the interactions betwen an antibody and its antigen

The peptide bond formation is only covalent

Funciton of antibodies

Neutralization: prevents their ability to infect cells ( blocking )

Opsonization: the antibody Fc regions binds to Fc receptors to help cells ingest & kill pathogens

Complement activation: antibodies trigger complement by activating C1

The main goal of the antibody in humans is to act as a messenger molecule to the immune system to actifivate the imune system

• al the activation of the imune system can over activate and the antibody can attect our own tisses —> which can result in immune issues

Fibrous Proteins: from structure to function

B conformation —> Soft, fexible filaments

Ahelix cross linked by dissulfide bonds —> tough insoluble protective structures with varying hardness & flexbility

Collagen triple helix —> high tensile strneght w/o stretch

Collagen

It is the most abundant protein in humans

• it provides structural support to extracellualr space of conenctive tissues

• very rigid and resistant to stretching (perfect matrix for skeletal)

It is made up of fibrous proteins

Synthesis of collagen

Translation and posttranslation modification (PTM)causes collagen synthesis

• PTM is esential for folding, asseemble & the structural integraty & funciton of the final collagen moelcule

Single pepetide chais become aggregated or assembled

The unique AA compositon of collagen

Collagen is a polymer of Gly-X-Y repeating where Y is frequently hydroxylysine or hydroxyproline and x is any other AA in colagen

• glycine is chosen because it is so small so it can fit into the rope like sturcture (because glycine is only H side chain)

  

Triple-stranded helix of collagen shows the significance of glycine

Triple-stranded helix of coallgen

It is a rigid structure, and they are intertwined

• the whole polpeptide chaine is Gly-X-Y

• three polypeotides (collagen a chains) are wound around one another in a rope-like triple helix

Fibrous protiens: from strucutr to fucntion

Collagen —> made. up of fibrous proteins

Collagen composition

rich in proline and Glycine (Gly-X-Y) (the Y can be hydroxy proline or hydroxy lysine and X is any another AA)

• hydroxy proline: invovles h bond formation that stabalizes the triple helix

• hydroxy lysine: the attachment sites of disaccharide moieties (galactose-glucose)

OH groups are important for h bonding between the peptide chain

Scurvy

Occurs due to the lack of vitamin C

• lack of vitamin c —> hdyroxylation is imapcted —> leads to weak colalgen formation

• loss of inter-strand hydrogen bond formaiton

Formation of crosslinks of colalgen

when the side chains of lysine are oxideized to form an aldehyde

• two aldehyde groups can attach with one another via aldol condensation and forms the lysinorleucine

  • the aldehydes are also two moieties —> forms a covalent bond