1 - Importance of albumin

Question 1

serum albumin

Answer 1

major protein (40 g/L) present in blood plasma (total protein content 70 g/L)

Question 2

Major functions of serum albumin

Answer 2

1. transporter of smaller, mostly hydrophobic, molecules,

2. major contributor (80%) of the osmotic swelling pressure of blood plasma

Question 3

electrophoresis of blood serum

Answer 3

Albumin is a major proportion of blood serum (or plasma) and it migrates rapidly to the positive electrode.

Many other molecules migrate to the same place, though they are different from albumin, as they are also attached to albumin

Question 4

forest plot

Answer 4

A graphical display to present the results of a meta-analysis.
Takes many studies that have examined the same thing, shows the outcome of each and of them all added together.

Question 5

alpha-Domain structures

Answer 5

a-helices tend to be packed pairwise in proteins with their hydrophobic residues pointing towards the molecule’s core.

Dimeric Rop protein, a small RNA- binding protein, adopts a four-helix bundle.

Question 6

structure of serum albumin

Answer 6

• HSA has an Mr of 66,500 and a pI of 5.67, and is almost entirely a-helical in content.
• consists of a single polypeptide chain containing 585 amino acids with 17 intra-chain disulfide bonds which pull the molecule into a series of large (L) and small (S) double loops.

Question 7

cysteines

Answer 7

form disulfide bonds

• AA sequence of albumin has an unusually high percentage of Cys
• The primary structure also contains a single free sulfhydryl (Cys-34)
• In circulating plasma 30% of free sulfhydryl Cys-34 is oxidised, and some preparations of serum albumin contain up to 20% albumin dimers, those are disulphide-bonded via their Cys-34s.

Question 8

Albumin the transporter

Answer 8

• contains multiple binding sites, for long-chain fatty acids, small heterocyclic, or aromatic carboxylic acids, and for metals.
• Cys-34 (SH-group) can bind ions of Cd, Au, Hg, Ag.
• N-terminal His-3 binds Cu(II), Ni(II)
• In fact, Cu(II) transport in the blood is primarily as a complex with albumin.

Question 9

drug transport

Answer 9

many hormones and drugs are transported by albumin.

These include Aspirin, AZT, Penicillin & Warfarin.

Question 10

importance of drug transport

Answer 10

Drugs compete for binding sites and small molecules, not transported on proteins, may be excreted by the kidney into the urine.

Question 11

3D structure of human serum albumin

Answer 11

The molecule actually adopts a heart shape with domains:

I in red

II in green

III in blue.

Question 12

Fatty acid binding

Answer 12

Here we see the structure when it is binding five molecules of the free fatty acid, myristic acid, a C14 fatty acid.

CH3 (CH2 ) 12COOH

Question 13

conformation change upon binding

Answer 13

There is a small change in conformation (shape) upon binding the fatty acids. This is a feature we’ll see in many of our structures.

Question 14

views of ligand binding

Answer 14

The largely hydrophobic fatty acid is held within a region of 3 or 4 a-helices created by the hydrophobic residues of HSA.

Question 15

Residue properties influence ligand binding

Answer 15

Similar views showing hydrophobic residues in green and polar (hydrophilic) residues in blue.
Whatever is in contact with the fatty acid is also hydrophobic.

Question 16

Surface view of structure

Answer 16

polar residues are found on the external surface and hydrophobic ones buried in the interior.

Question 17

Metal ion binding

Answer 17

Main chain atoms and side chain atoms from a variety of different amino acids contribute to metal ion binding.

Question 18

Serum albumin (1e7a) binding to propofol (an anaesthetic)

Answer 18

Propofol is insoluble. albumin is unable to cross the blood-brain barrier, so if you don’t want a drug to reach the brain, attach it to albumin

Question 19

Reactive Cys34 as an attachment point

Answer 19

1/35 is not bound to each other, not forming the disulphide bond, meaning that there are only 17 bonds and 34 cysteine atoms bound to each other. the remaining 35th cysteine can bind directly to rubicin

Question 20

MTX-HSA accumulation studies

Answer 20

MTX-HSA has a slower accumulation/ release than MTX.

Though the start dose is lower, HSA allows a higher accumulation of dosage

Question 21

Evans blue

Answer 21

• very high affinity for serum albumin.
• excitation peaks at 470 nm and 540nm, emission peak at 680nm.
• named after Herbert Mclean Evans
• used as viability assay
• permeability of the blood-brain barrier to macromolecules

Question 22

Many binding sites for many small molecules

Answer 22

Important: Serum albumin’s structure and properties allow it to bind and transport a diverse range of small molecules