Table 3 Reasons for non-conservation of disulphide bonds between homologous proteins that share high sequence similarity.

with SS

without SS

Rubisco, large subunit (c.1.14.1)

3rub

8ruc

172–192

94.7

Crystallographic artifact

Not clear if functionally significant or formed during crystallization period

[83]

Purple acid phosphatase (d.159.1.1)

1ute

1qhw

163–221

84.7

Crystallographic artifact

No indication crosslink in electron density map

[84]

VHS domain (a.118.9.2)

1ujk

1juq

33–76

72.7

Crystallographic artifact

Not favorable to accommodate cross link

-

DnaQ-like 3'-5' exonuclase (c.55.3.5)

1noy

1ih7

41–55

63.9

Crystallographic artifact

Not favorable to accommodate cross link

-

Transferrin (c.94.1.2)

-

1gv8

2tmp

-

-

Fragments of domains

1gv8 – fragment of N-terminal domain of the intact protein, ovotransferrin

2tmp – only 1–122 residues of N-terminal domain of TIMP

[85]

Annexin (a.65.1.1)

-

1scf

-

-

Fragments of domains

Partial structure

-

G proteins (c.37.1.8)

-

1ryh

1mh1

1dsb

-

-

Fragments of domains

Partial structure

-

Glutathione S-transferase, N-terminal domain (c.47.1.5)

1k0m

1rk4

24–59

98.6

Structural transition

A typical glutathione S-transferase but with a glutaredoxin-like active site. Disulphide bond facilitates a redox-controlled structural transition from monomeric to dimeric state

[49]

Prion-like (d.6.1.1)

1i4m

1uw3

179–214

91.2

Structural transition

Rearrangement of disulphide bonds helps in conformationallly altering the prion protein to pathogenic oligomeric form.

[50]

Alpha-macroglobulin receptor domain (b.2.4.1)

1ayo/1bv8

1edy

17–132

66.2

Structural transition

Major conformational differences between human/bovine and rat RBD

[60]

Papain-like (d.3.1.1)

1qdq

3pbh

148–252

88.9

Stabilization of local structure

Disulphide bond increases the conformational flexibility of the occluding loop, although the conformational stability of the overall structure is little affected.

[54]

Parvalbumin (a.39.1.4)

1a75

1bu3

11–33

88.7

Stabilization of local structure

This disulphide bond is unique to Whiting parvalbumin and stabilizes the two helical hairpin although the conformational stability of the overall structure is little affected.

-

Dipeptidyl peptidase IV/CD26, N-terminal domain (b.70.3.1)

1nu6

1orv

328–339

85.7

Increased activity

Adenosine deaminase (ADA) binds stronger to the disulphide bonded human protein than in porcine.

[51]

Ricin B-like (b.42.2.1)

2aai

1m2t

1onk

20–39

72.6

Increased activity

Reduced cytotoxicity in mistle toe lectin

[52]

Xylanase/endoglucanase 11/12 (b.29.1.11)

1yna

1xnd

110–154

59.5

Increased activity

Increased thermostability due to compounding effect of disulphide bond with increase in the density of charged particles

[53]

Mycobacterial antigens (c.69.1.3)

1f0n

1dqz

87–92

72.1

Unassigned role

Not obvious from the structural differences if the antigens have different biological roles

[55]

Quinoprotein alcohol dehydrogenase-like (b.70.1.1)

1g72

1kb0

1kb9

144–167

33.2

Unassigned role

No structural or functional role assigned

[56]

Subtilases (c.41.1.1)

1dbi

1thm

137–139

61.6

Unassigned role

C-X-C disulphide bridge is hypothesised to enhance the thermaostability

[57]

Hemorrhagin (d.92.1.9)

1bud

4aig

157–164

49.2

Unassigned role

No direct evidence if the variable disulphide bridges in the C-terminal subdomain hemorrhagin family of enzymes lead to differences in their hemorrhagic activity.

[58]