Globular and Fibrous Proteins

Globular and Fibrous Proteins

1. Globular

   • Hemeproteins
     • Haemoglobin
       • found only in RBCs
       • transport oxygen around the body
         • can also transport H+ and CO2
       • composed of 2 identical dimers
         • held together by hydrophobic interactions
           • hydrophobic AAs are on the interior of the monomer and on the outside surface in contact with the other polypeptide of the same dimer
         • every haemoglobin can bind to 4 oxygen molecules
     • Myoglobin
       • present in heart and skeletal muscles
       • reservoir and carrier of oxygen
       • single polypeptide
         • folded in 8 stretches of alpha-helices
           • stabilised by hydrophobic interactions
         • non-polar AAs in the interior
         • polar and charged AAs on the surface
       • oxygen bound by iron
     • Heme structure
       • Iron can form 6 bonds
         • 4 with porphyrin nitrogens
         • 2 additional: 1 above and 1 below ring

2. Fibrous

   • Collagen
     • 3 polypeptides wound in a triple helix
       • made of alpha chains
         • rich in Pro and Gly
         • also contains: hydroxyproline and hydroxylysine, which stabilises structure with H bonds
     • Fibril forming
       • Type 1
         • Skin, bone tendon, blood vessels, cornea
       • Type 2
         • Cartilage, intervertebral disc
       • Type 3
         • Blood vessels, fetal skin
     • Network forming
       • Type 4
         • Basement membrane
       • Type 7
     • Fibril associated
       • Type 9
         • Cartiliage
       • Type 12
         • Tendons, ligaments
   • Elastin
     • In connective tissues
       • Lungs, arteries, ligaments
     • Can be stretched and return to their normal length
     • Made from tropoelastin
       • rich in small, non-polar AAs
       • It is secreted in the extracellular space
         • Fibrillin acts as a scaffold for tropoelastin
       • Cross links form between lysyl side chains
         • Desmosine
   • In extracellular matrix