Cysteine overview

Question 1

Cysteine:

Answer 1

Cys or C

Question 2

Description:

Answer 2

• Polar sulfhydryl

-Forms disulfide crosslinks

-Crosslinks many proteins: e.g. keratins in hair

0

-It doesn’t like the alpha helix, but doesn’t mind
strand and turn.

Question 3

Properties:

Answer 3

• It can form Cys-Cys bridges with other cysteines

-It can bind metals (especially Zn and Cu).

-The S-H group is very reactive

Question 4

Comparisons:

Answer 4

-Homologous to Ser (substitute S for O), but important differences…

-Cys more acidic (pK = 8.5)

-Thiolate (deprotonated –S-)

-Quite common

-Proton donor in several catalytic mechanisms - Or acceptor - with small shift in pK

-Less H-bonding propensity than OH

Question 5

bonds:

Answer 5

• No abbrev. ( Cys-Cys )
• Actually – just 2 cysteines joined
• Cys has strong potential to form SS bridges
  – AKA Disulfides
• Additional covalent link leads to stability

-Redox reaction