Structural studies of chitin
active enzymes
A variety of organisms possess
a chitinolytic capacity. These
include plants, microorganisms such as bacteria and fungi, arthropods
and some
of the other higher animals such as amphibians, fish and mammals.
Chitinase is one of the major weapons for the defense against pathogens
not
only in higher plants and seaweeds but also in fish and mammals.
Microorganisms
digest the chitinous substrates for nutrients or hydrolyze their own
chitinous
cell walls for cell proliferation, while arthropods such as insects and
crustaceans produce chitinase in order to degrade the exo-skeleton
during
eckdysis. Chitinases are classified into glycoside
hydrolase families 18 and 19, and therefore possess exo acting
retaining
mechanism and endo acting inverting mechanism, respectively.
Brassica
juncea
chitinase
Homology model of the catalytic domain
Ribbon cartoon of the catalytic cleft of BjCHI3
homology
model. Completely conserved parts are shown in red and amino acids
mutated are
shown in green.
Surface
diagram of the catalytic cleft of BjCHI3 homology model is shown with
the
indicated amino acid side chains for mutation studies. Modeled chitin
chain is
docked according to the suggestions of earlier authors (Sasaki, C.
et al., 2003).
Reference
Ce Mun Tang, Mee-Len Chye,
Sathishkumar
Ramalingam, Ouyang Shi-Wen, Kai-Jun Zhao, Wimal Ubhayasekera and Sherry Mowbray (2004). Functional
analysis of the
chitin-binding domains and the catalytic domain of Brassica juncea
chitinase
BjCHI1. Plant Mol Biol, 56, 285-298.
Dioscorea opposita (yam) chitinase E
The homology
model of Dioscorea opposita
(yam)
chitinase E. Catalytic residues Glu138 and Glu147 are shown in
ball-and-stick
in black. Predicted insertions (Ins1) and deletions (Del1-4) compared
to barley
chitinase structure are marked in black and orange-red respectively.
Modeled
chitin chain is docked according to the suggestions by (Sasaki, C. et al., 2003)
Reference
Takuji Mitsunaga, Minoru Iwase,
Wimal Ubhayasekera, Sherry
Lynn
Mowbray and Daizo Koga (2004). Molecular cloning of a genomic DNA
encoding yam
class IV chitinase and homology modeling. J. Bioscience,
Biotechnology and
Biochemistry, 68(7), 1508-17.
Manduca sexta chitinase
Ribbon cartoon representation
of the homology models of Manduca sexta chitinase catalytic domain and
chitin binding domain with
a fancy model of the linker
Space-filling
representation of the homology models of Manduca sexta chitinase catalytic domain and
chitin
binding domain with a fancy model of the linker
Red-catalytic residues (E127,
D125); Blue – possible
N-glycosylation sites (N66 & N284, NetNGlyc program); Orange –
possible
O-glycosylation sites (many S/T residues, NetOGlyc program); Green in
catalytic
domain – conservation compared to pdb entry 1LG1; Green in ChBD (chitin
binding
domain) – conserved Cys compared to other family members; Skyblue in
catalytic
domain- conserved residues important in substrate binding; Skyblue in
ChBD-
conserved residues possibly involved in chitin binding; Orange/red-
chitin
polysaccharide
Created by Wimal
Ubhayasekera 2001-11-20 and modified on 2005-05-03
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