Serum albumin

• functions of human serum albumin

  • transport
  • oncotic regulator
• human serum albumin is rich in

  • alpha helices
  • disulphide bonds
• albumin can transport different substances

  • in several sites of its structure
  • if they have a covalent or non-covalent bond between them
• human serum albumin is produced in the

  liver
• what is human serum albumin (HSA)

  major protein in the blood plasma
• HSA transports mostly small, hydrophobic molecules
• alpha helix domain structure:

  • packed in pairs in proteins
  • hydrophobic residues pointing towards the molecule's core
• HSA structure:

  • Mr=66,500
  • pl=5.67
  • single polypeptide chain
  • 585 amino acids
  • 17 intra-chain disulphide bonds
• the disulphide bonds in HSA pull the molecule into large and small double loops
• structure of HSA

  labels:

  A) double loops

  
• most of HSA is in alpha helices
• evolution of HSA

  • L (original gene) duplicated twice
  • LLL mutated
  • LSL duplicated twice
  • LSL-LSL-LSL
• L DNA coding for L loop, S DNA coding for S loop
• 35 out of 585 amino acids are cysteines
• the primary structure contains a single free sulfhydryl (Cys-34) of which 30% are oxidised in circulating plasma
• albumin dimers 


  disulphide bonded via Cys-34s
• Cys-34 can bind ions of

  • Cd
  • Au
  • Hg
  • Ag
• the N-terminal of His-3 binds

  • Cu(II)
  • Ni(II)
• albumin transports:

  • long-chain fatty acids
  • small heterocyclic/aromatic carboxylic acids
  • metals
• Cu(II) transport in the blood is primarily with albumin
• albumin drug transport

  • Aspirin
  • AZT
  • Penicillin
  • Warfarin
• importance of HSA binding to drugs

  • because drugs compete for binding sites
  • small molecules not transported on proteins could be excreted by the kidney into the urine
• when molecules bind to HSA

  there is a small conformational change
• when a fatty acid binds to HSA it is held within a region of 3 or 4 alpha helices created by the hydrophobic residues of HSA
• HSA adopts a heart shape
• polar residues are found


  on the external surface
• hydrophobic residues are found

  in the interior of the molecule
• free thiols are good

  nucleophiles
• HSA binds to

  • Propofol (anaesthetic)
  • Halothane (anaesthetic)
  • ibuprofen
• reactive Cys-34 acts as an attachment point
• Evans blue has very high affinity for HSA with excitation peaks at 470nm and 540nm, emission peak at 680nm
• Evans blue is used as a

  viability assay
• albumin cannot get through to tissues unless there is damage to the vessels
• Evans blue used to measure blood volume, using concentrations to calculate