The role of pseudo-endoglucanases in the evolution of nematode cell wall-modifying proteins

J Mol Evol. 2010 May;70(5):441-52. doi: 10.1007/s00239-010-9343-1. Epub 2010 Apr 23.

Abstract

In this article, the characterization and evolution of pseudo-endoglucanases and a putative expansin-like gene in the migratory nematode Ditylenchus africanus are described. Four genes were cloned with a very high similarity to the endoglucanase Da-eng1, which, however, lack a part of the catalytic domain most probably due to homologous recombination. Owing to this deletion, at least one of the catalytic residues of the corresponding protein is missing, and hence these genes are possibly pseudogenes. In two of the pseudo-endoglucanase genes, the deletions cause a frameshift (Da-engdel2, Da-engdel4), while two others (Da-engdel1, Da-engdel3) code for protein sequences with an intact carbohydrate-binding module (CBM). Recombinant proteins for Da-ENG1, Da-ENGDEL1, and Da-ENGDEL3 were demonstrated to bind to cellulose, while only Da-ENG1 showed cellulose-degrading activity. This indicates that Da-ENGDEL1 and Da-ENGDEL3 which lack cellulase activity, could still exert a function similar to cellulose-binding proteins (CBPs). Next to the pseudo-endoglucanases, a putative expansin-like gene (Da-exp1) was identified, consisting of a signal peptide, an expansin-like domain, and a CBM. This domain structure was never found before in nematode expansin-like proteins. Interestingly, the CBM of the expansin-like gene is very similar to the endoglucanase CBMs, and a conserved intron position in the CBM of nematode endoglucanases, expansin-like genes, and CBPs indicates a common origin for these domains. This suggests that domain shuffling is an important mechanism in the evolution of cell wall-modifying enzymes in nematodes.

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Cell Wall / enzymology
  • Cell Wall / physiology
  • Cellulase / genetics*
  • Cellulase / metabolism
  • Evolution, Molecular*
  • Gene Deletion
  • Genes, Helminth
  • Molecular Sequence Data
  • Protein Binding
  • Pseudogenes
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Sequence Alignment
  • Tylenchida / enzymology*
  • Tylenchida / genetics*

Substances

  • Recombinant Proteins
  • Cellulase