A. Rehman et Dp. Jasmer, Defined characteristics of cathepsin B-like proteins from nematodes: inferred functional diversity and phylogenetic relationships, MOL BIOCH P, 102(2), 1999, pp. 297-310
Numerous cathepsin B-like protein sequences (CBLs) have been reported from
nematodes. However, the relationships among these proteins remain unclear.
Here, expression of several CBL transcripts in the gut of the parasitic nem
atode Haemonchus contortus was demonstrated. To assess potential functional
diversity, multiple nematode CBL sequences were compared with known functi
onal domains of cathepsin B. These domains included the occluding loop, S2'
and S2 subsites, and the pro region. Four groups of CBLs were defined base
d on variable characteristics in the occluding loop region, which incorpora
tes a portion of the S2' subsite. Further diversity was observed in amino a
cids expected to contribute to the S2 subsite. In addition, short signature
sequences near the cysteinyl active site region characterized known CBLs o
f parasites from the orders Strongylida and Rhabditida. The criteria establ
ished were used to identify two predicted CBLs from parasitic (Ascaris suum
) and free-living (Caenorhabditis elegans) nematodes as potential orthologu
es, and provided a basis to evaluate orthologue status of other CBLs. Varia
bility in the domains analyzed suggests substantial functional diversity in
enzymatic properties of nematode CBLs. Results suggest that the selective
amplification and evolution of distinct CBL lineages has contributed to dif
ferences in CBLs among species and groups of nematodes. Nutrient digestion
is one potential factor promoting CBL diversification in these organisms. (
C) 1999 Elsevier Science B.V. All rights reserved.