| Natural products are simply the molecules produced by biological systems. My studies examined the structure, function, and chemical biodiversity of two types of natural products, FMRFamide-like neuropeptides and defensive dolichodial-like compounds from walkingstick insects (Order Phasmatodea).; FMRFamide-like neuropeptides (FLPs) make up one of the largest known neuropeptide families. The first member was identified in 1977 as a cardioactive component of extracts from clam. FLPs are characterized by an N- to C-terminal gradient of conservation, with subfamilies produced on the same gene having similar C-terminal sequences. The canonical C-terminal motif of FLPs is Arg-Phe-NH 2. They are involved in a wide variety of biological and behavior processes. They have been identified in humans and are particularly well represented in invertebrates.; First, my study examined evolutionary relationships among several FLP subfamilies in the nematode Caenorhabditis elegans. Using bioinformatics tools and precursor protein sequence comparisons, I identified several important features of FLP neuropeptides and their precursor proteins and genes. Also, some subfamilies of FLP neuropeptides and their precursor proteins were categorized into groups based on a number of similar features.; Next, I examined the structure/function relationships for a particular subfamily of two FLPs (EMPGVLF-NHZ and DFDGAMPGVLRF-NHZ) from C. elegans of the FLP18 subfamily. These peptides have been demonstrated to regulate feeding behavior in C. elegans by activating the NPR-1 receptor. NMR pH titration experiments and chemical shift indexing were used to probe transient hydrogen bonding and electrostatic interactions between aspartate sidechains and amide protons. These results indicate that the longer of the two native C. elegans peptides possesses N-terminal structure, stabilized by a hydrogen bonding network, which reduces its potency on the NPR-1 receptor relative to the shorter peptide.; To examine non-polypeptide natural products, a novel microsample NMR probe was used to examine the chemical biodiversity of walkingstick insects. The results show the following: (1) Anisomorpha buprestoides produces two stereoisomers of dolichodial in its defensive spray, (2) Peruphasma schultei produces only a single isomer (Peruphasmal) of the same compound, and (3) defensive secretions of both species contain glucose (previously unreported from walkingstick insect defensive secretions). These findings would not have been possible using other NMR technologies. |
