The GH18 family of chitinases: Their domain architectures, functions and evolutions

Abstract

The glycoside hydrolase 18 (GH18) family of chitinases is a multigene family that plays various roles, such as ecdysis, embryonic development, allergic inflammation and so on. Efforts are still needed to reveal their functional diversification in an evolutionary and systematic manner. We collected 85 GH18 genes from eukaryotic representatives. The domain architectures of GH18 proteins were analyzed and several conserved patterns were identified. It was observed that some (11 proteins) GH18 members in Ecdysozoa or fungi possess repeats of catalytic domains and/or chitin-binding domains (ChtBs). The domain repeats are likely to meet requirements for higher efficiency of chitin degradation in chitin-containing species. On the contrary, all vertebrate GH18 proteins contain no more than one catalytic domain or ChtB. The results from homologous analysis, domain architectures, exon arrangements and synteny loci supported two evolutionary paths for the GH18 family. One path experienced gene expansion and contraction several times during evolution, covering most of GH18 members except CHID1 (stabilin-1 interacting partner) and its homologs. Proteins in this path underwent frequent domain gain and loss, as well as domain recombination, that could achieve versatility in function. The other path is comparatively conserved. The CHID1 gene evolved without gene duplication except in Danio rerio. Domain architectures of CHID1 orthologs are all identical. The diverse phylogeny of the GH18 family in arthropod is also presented.

Molecular characterization and expression analysis of five chitinases associated with molting in the Chinese mitten crab, Eriocheir sinensis

“…The CBD was also absent in group 1 chitinases MnCht1A and MnChtB and group 3 chitinases MnCht3A, MnCht3B, and Pjcht3A, suggesting that the CBD might be lost during gene duplication (Huang et al, 2012;Fig. 3).…”

“…In crustaceans, chitin is a vital component of the cuticular exoskeleton that serves as a mechanical support and protective barrier. In order to grow and develop, crustaceans need to degrade the old exoskeleton periodically and synthesize a new one during molting (Huang et al, 2012). The degradation of chitin is accomplished by a binary enzyme system composed of chitinases (EC 3.2.1.14) and N-acetyl-β-glucosaminidases (NAG, EC 3.2.1.30).…”

Cooperative Degradation of Chitin by Extracellular and Cell Surface-Expressed Chitinases from Paenibacillus sp. Strain FPU-7

“…This multimodular enzyme, however, does not contain any known carbohydrate-binding modules, which are often present in endo-type chitinases (41). Thus far, microbial chitinases with two catalytic domains have been identified in the Chlorella virus CVK2 (42), the hyperthermophilic archaeon Thermococcus kodakaraensis strain KOD1 (43), and the Gram-negative marine bacterium Microbulbifer degradans strain 2-40 (44).…”

Dual silencing of long and short Amblyomma americanum acidic chitinase forms weakens the tick cement cone stability

“…1B). The GH-18 family is characterized by: (1) signal peptide, (2) Ser/Thr-rich linker regions that may be heavily glycosylated located in the N-or Cterminal region linking the signal peptide, catalytic domain and chitin binding domain (Arakane et al, 2003;Huang et al, 2012), (3) one to several GH-18 catalytic domains that have conserved DXDXE and/ or SXGG motif (Henrissat, 1991;Watanabe et al, 1993;Tsuji et al, 2010), and (4) none to five chitin binding domains characterized by the CX 67 -FX 67 -CX 2 -YX 7 -CX 919 -CX 46 -FX 47 -CX 512 -C motif (Fuhrman et al, 1995;Tellam, 1996). In arthropods, the typical GH-18 chitinase catalytic domain is characterized by four signature amino acid sequence motifs including active site 'FDG(L/F)DLDWE(Y/F)P' containing the conserved DXDXE motif (Thomas et al, 2000;Lu et al, 2002), Arakane and Muthukrishnan, 2010).…”