Submitted to: Journal of Parasitology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/25/2001
Publication Date: 10/1/2001
Citation: Rhoads, M.L., Fetterer, R.H., Urban Jr, J.F. 2001. Cuticular collagen synthesis by ascaris suum during development from the third- to fourth-larval stage; identification of a potential chemotherapeutic agent with a novel mechanism of action. Journal of Parasitology. 87:1144-1149 (2001) Interpretive Summary: The swine round worm, Ascaris suum, is responsible for significant economic losses by reducing production efficiency and causing organ condemnations at slaughter due to pathology produced by parasite larval stages. Development of novel controls can be enhanced by a knowledge of the biochemical mechanism underlying the process of molting, an essential process in the growth and development of all nematodes. The results demonstrate that A. suum larvae release collagen monomers, dimers and trimers coincident with molting which reflects the increased translation of collagen gene products associated with the synthesis of a new cuticle. A protease inhibitor was shown to interact specifically with monomeric collagen preventing a critical step in cuticle synthesis and resulting in the inhibition of molting.
Technical Abstract: The dominant proteins released by Ascaris suum during development in vitro from the L3 to L4 stage were identified as collagenous cuticular proteins by sequence analysis and susceptibility to digestion by collagenase. Under reducing SDS-PAGE, the collagen proteins separated into 3 groups with molecular weights estimated at 1) 32 kDa, 2) 54, 57, and 60 kDa, and 3) 71, ,78, 83, and 91 kDa. The 32-kDa protein represents monomeric collagen; the 54-60 and 71-91 kDa components represent dimeric and trimeric forms respectively, polymerized by non-reducible cross-links. Furthermore, the release of these forms of collagen was developmentally regulated as exemplified by a sequential temporal progression from monomeric to dimeric to trimeric forms indicated by electrophoretic analysis. The data suggest that collagen released in vitro during development of A. suum L3 to L4 reflects the increased translation of collagen gene products and their initial assembly into higher molecular weight molecules associated with th synthesis of the L4 cuticle. A biotinylated dipeptidyl fluoromethylketone cysteine protease inhibitor (Bio-phe-ala-FMK) bound specifically to the 32- kDa collagen and, to a lesser extent, to a 30-kDa protein; binding was dependent on the presence of DTT and was prevented by iodoacetamide. Because cysteine residues play an essential role in the initial assembly of the collagen monomers into the higher molecular weight oligomers present in the mature nematode cuticle, inhibition of molting of A. suum L3 to L4 by the cysteine protease inhibitor Z-phe-ala-FMK, reported previously (Rhoads et al., 1998), might be due to its binding to thiol groups of collagen monomers during a critical phase of collagen assembly.