Universität zu Köln

Sharma, Kanika (2018). Olfactory coding in vertebrates: a novel tuning mechanism for receptor affinity and evolution of the olfactory receptor repertoire. PhD thesis, Universität zu Köln.

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Abstract

Information about our environment is to a large extent carried by the chemical senses, and in particular the olfactory sense. Vertebrates perceive thousands of diverse odor molecules with a supply of a wide range of essential information ranging from localising prey or food, avoiding predators, mating behaviour, to social communication. Because olfactory receptor proteins play such an essential role in the specific recognition of diverse stimuli, understanding how they interact with and transduce their cognate ligands is a high priority. This constitutes one of the most complex ligand/receptor binding problems in biology due to the sheer quantity of potential odor molecules facing a limited albeit huge number of different olfactory receptors. Most olfactory receptors are G-protein coupled receptors and form large gene families. One type of olfactory receptors is the trace amine-associated receptor family (TAAR). TAARs generally recognize amines and one particular member of the zebrafish TAAR family, TAAR13c, is a high affinity receptor for the death-associated odor cadaverine, which induces aversive behavior. Here we have modeled the cadaverine/TAAR13c interaction by multistep docking. By exchanging predicted binding residues via site-directed mutagenesis, and measuring the activity of the mutant receptors, we confirmed a binding site for cadaverine at the external surface of the receptor, in addition to an internal binding site, whose mutation resulted in complete loss of activity. Elimination of the external binding site generated supersensitive receptors which suggests this site to act as a gate, limiting access of the ligand to the internal binding site and thereby downregulating the affinity of the native receptor. Potentially related mechanisms have been described for non-olfactory G-protein coupled receptors. The topology of TAAR-expressing neurons in the teleost olfactory epithelium has not been described yet. We have investigated representative taar genes from three classes to test the principle of partial spatial segregation known from other olfactory receptor families for the TAAR family. We report that expression of taar genes is intermingled with expression zones of odorant receptor genes, which in fish share a single sensory surface with TAARs. Individual taar genes show distinct, albeit broadly overlapping expression zones. In the third part of my thesis I investigated the genome of a cartilaginous fish, Scyliorhinus canicula, commonly known as small spotted catshark in order to delineate its chemosensory receptor repertoire: OR, V1R/V2R, TAAR, and T1R/T2R. This is the first repertoire described for a true shark, an important intermediate in the evolution of vertebrates. In contrast to bony vertebrates, but very similar to a chimera (elephant shark), the olfactory receptor repertoire of catshark is dominated by the V2R family.

Item Type:	Thesis (PhD thesis)
Creators:	Creators Email ORCID ORCID Put Code Sharma, Kanika ksharma997@gmail.com UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-101476
Date:	7 September 2018
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Biology > Institute for Genetics
Subjects:	Life sciences
Uncontrolled Keywords:	Keywords Language PhD Thesis English Bioinformatics English Evolution English
Date of oral exam:	26 October 2018
Referee:	Name Academic Title Korsching, Sigrun Prof. Dr.
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/10147