BIOINORGANIC CHEMISTRY A Short Course Second Edition

PROTEINS 33

different metal ions (Asp - M 1 M 2 ). Some examples are shown in Figure 2.5 , but
it should be remembered that these modes are not all - inclusive. Metal ions
exhibit a great variety of binding partners and bonding modes in biological
species, not only to amino acid side - and main - chain atoms, but also to water,
sugars, atoms of DNA and RNA, and other convenient atoms or ions in the
physiological milieu.

2.2.2 Protein Structure,

All proteins have at least three levels of structure: primary, secondary, and
tertiary. Proteins with more than one polypeptide chain — hemoglobin and
nitrogenase are examples — also possess quaternary structure. The primary,

Figure 2.5 Common metal ion bonding modes to amino acid side chains in proteins.

+H 3 NC

H

H 2 C

CH 2

S

CH 3

M

COO-

+H 3 NC

H

CH 2

O(H)

M

COO- +H 3 NC

H

CH

O(H) CH 3

M

COO-

+H 3 NC

H

CH 2

M S

• CHOO

+H 3 NCCOO-

H

CH 2

C

O O

HC 2

M

• 
  

+H 3 NC

H

CH 2

M O(H)

COO-

H 2 C

N

N

+H 3 NC

H

M

M

α COO-

β

γ

δ δ

ε

glutamic acid, glutamate,

Glu, E

aspartic acid, aspartate,

Asp, D

O O

+H 3 NC

H

H 2 C

M 2 M 1

• 
  

COO-

tyrosine, Tyr, Y

Serine, Ser, S threonine, Thr, T

histidine, His, H cysteine, cys, C methionine, Met, M

α

β

γ

α

β

γ

δ

α

β

δ 2 δ 1

ε 2 ε 1

α

β

γ γ

δ

C

α

β

γ

α

β

γ