Nematodes functional biology

Current understanding of parasitism by T. spiralis is compartmentalized, and so glycoprotein function has been considered in the context of one compartment or another. However, LI larvae of T. spiralis have evolved under selective pressure to parasitize both intestine and muscle. Biological economy may require a duality of function in larval glycoproteins such that they are able to perform distinct roles in each of the two niches. Dualism is common in proteins, and elucidation of such properties in parasitic nematode products would provide unique insights into the basis of host adaptation. 

The term polyproteins is used for two different types of entity. The first refers to precursor polypeptides which are cleaved post-translationally into biologically active proteins or peptides of quite different functions. Examples of these include polyproteins of viruses and some prohormones of vertebrates (reviewed in Kennedy, 2000b). The other type is large proproteins which comprise tandem repetitions of identical or similar polypeptides that are post-translationally cleaved into multiple copies of biochemically similar functional entities. The nematode polyprotein allergens/antigens (NPAs) fall into this class (Fig. 16.1). 

The isolation of JH III from C. iria and C. aromaticus, the high concentrations found in C. iria throughout development and the extraction of structurally similar compounds from closely related species as well as other plant species suggests that this compound may play an important biological function(s) in these plants. At this point, the nature of this role is speculative however, it is possible that JH III may be involved in plant-insect, plant-plant, plant-nematode or plant-fungal interactions. 

The external surfaces of parasitic helminths, termed the tegument in cestodes and trematodes, and the cuticle in nematodes, are adapted to serve a wide range of biological functions. Though most research has focused on structural aspects or their roles in immune evasion (Chapter 16) and nutrient absorption, the external surfaces of helminths also serve important roles in locomotion, excretion and regulation of electrochemical and osmotic gradients. 

The rigid cuticle that is the external surface of nematodes is quite distinct from the tegument of cestodes and trematodes. Nematodes also possess a functional gut that ends in a muscularly controlled rectum. Although the various niches occupied by nematodes have led to evolutionary surface adaptations particularly suited for specific environments, the general features of their surface biology are well conserved. 

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