exceptions such as the mannanases of Bacillus sp. JAMB-602 and Bacillus JAMB750 [118] (http://www.cazy.org/CBM23_characterized.html) and the Bacillus
sp. SN5 xylanase [131].
5.4 Structural Features
In the glycoside hydrolase classification system, related families of enzymes that
share common ancestry, structural fold, catalytic residues, and mechanism of catalysis are grouped in clans [132]. In this system, xylanases are grouped in four
different clans (GH-A, GH-C, GH-F, and GF-M), while all known families of
mannanases, except GH134, belong to clan GH-A (Table 6). Among xylanases,
those that belong to GH98 and GH141 are not yet a member of any known clan, and
the same holds true for GH134 mannanases (Table 6). Most of the hemicellulases
belong to the clan GH-A, which also contains other families with (α/β) 8 -barrel fold, a
structure most common among all known enzyme folds. Roughly, one out of ten
enzymes has an (α/β) 8 -barrel fold [143], and in addition to GH-A, members of the
clans GH-D, GH-H, and GH-K exhibit this folding motif. The (α/β) 8 -barrel is
composed of eight parallel β-strands that makes the inner β-barrel sheet that is
Table 6 Xylanases and mannanases that belong to different clans and their protein fold
Enzyme
Family Clan
Fold
PDB code
(example)
References
Endo-β-1,4-xylanase
(EC 3.2.1.8)
5
GH-A (β/α) 8
1NOF
Larson et al.
[133]
8
GHM
(α/α) 6
1H12
Van Petegem
et al. [134]
10
GH-A (β/α) 8
2UWF
a
Mamo et al.
[135]
11
GH-C β-jelly roll
2NQY
a
Unpublished
30
GH-A (β/α) 8
3KL5
St John et al.
[136]
43
GH-F 5-blade
β-propeller
3CU9
b
Alhassid et al.
[137]
51
GH-A (β/α) 8
3UG3
b
Im et al. [138]
98
–
–
2WMI
b
Higgins et al.
[139]
141
–
(β)-helix
5MQP
b
Unpublished
Endo-β-1,4-mannanase
(EC 3.2.1.78)
5
GH-A (β/α) 8
3JUG
a
Zhao et al. [140]
26
GH-A (β/α) 8
4YN5
a
Unpublished
113
GH-A (β/α) 8
5YLI
a
You et al. [141]
134
–
–
5JTS
Jin et al. [142]
a Enzymes from alkaliphiles
b
Representative structures that are neither xylanase nor mannanase
266
G. Mamo
sp. SN5 xylanase [131].
5.4 Structural Features
In the glycoside hydrolase classification system, related families of enzymes that
share common ancestry, structural fold, catalytic residues, and mechanism of catalysis are grouped in clans [132]. In this system, xylanases are grouped in four
different clans (GH-A, GH-C, GH-F, and GF-M), while all known families of
mannanases, except GH134, belong to clan GH-A (Table 6). Among xylanases,
those that belong to GH98 and GH141 are not yet a member of any known clan, and
the same holds true for GH134 mannanases (Table 6). Most of the hemicellulases
belong to the clan GH-A, which also contains other families with (α/β) 8 -barrel fold, a
structure most common among all known enzyme folds. Roughly, one out of ten
enzymes has an (α/β) 8 -barrel fold [143], and in addition to GH-A, members of the
clans GH-D, GH-H, and GH-K exhibit this folding motif. The (α/β) 8 -barrel is
composed of eight parallel β-strands that makes the inner β-barrel sheet that is
Table 6 Xylanases and mannanases that belong to different clans and their protein fold
Enzyme
Family Clan
Fold
PDB code
(example)
References
Endo-β-1,4-xylanase
(EC 3.2.1.8)
5
GH-A (β/α) 8
1NOF
Larson et al.
[133]
8
GHM
(α/α) 6
1H12
Van Petegem
et al. [134]
10
GH-A (β/α) 8
2UWF
a
Mamo et al.
[135]
11
GH-C β-jelly roll
2NQY
a
Unpublished
30
GH-A (β/α) 8
3KL5
St John et al.
[136]
43
GH-F 5-blade
β-propeller
3CU9
b
Alhassid et al.
[137]
51
GH-A (β/α) 8
3UG3
b
Im et al. [138]
98
–
–
2WMI
b
Higgins et al.
[139]
141
–
(β)-helix
5MQP
b
Unpublished
Endo-β-1,4-mannanase
(EC 3.2.1.78)
5
GH-A (β/α) 8
3JUG
a
Zhao et al. [140]
26
GH-A (β/α) 8
4YN5
a
Unpublished
113
GH-A (β/α) 8
5YLI
a
You et al. [141]
134
–
–
5JTS
Jin et al. [142]
a Enzymes from alkaliphiles
b
Representative structures that are neither xylanase nor mannanase
266
G. Mamo