Ligand repertoire

The evolutionary path followed in teleost fish development has been distinctly different from that pursued in tetrapods, with massive diversification in the TAAR family but with a total lack of any expansion in the ORA family. It is expected that the respective ligand repertoires and corresponding biological function will turn out to be distinctly different as well. However, extensive progress in deorphanizing teleost olfactory receptors will be necessary to understand the evolution of ligand repertoires for the olfactory receptor gene families. 

A similar approach was applied in the study of the silkmoth bombykol pheromone receptor (Sakurai et al. 2004 Nakagawa et al. 2005), a receptor for honeybee queen substance p-oxo-2-decenoic acid (Wanner et al. 2007), and a ligand repertoire for Anopheles ORs (Lu et al. 2007). In these cases, however, coexpression of Ga15 was not necessary, but expression of one member of the Or83b family was absolutely necessary. The molecular mechanisms for signal transduction are discussed in Sect. 4. 

Eighteen human chemokine receptors have been identified to date (Murphy et al., 2000 Murphy, 2002), ten of which belong to the CC family (Table II). The ligand repertoire of chemokine receptors is typically class restricted, that is to say, CC chemokine receptors are activated only by CC... 

Among the receptors for the retinoids (RAR and RXR) there are at least three subtypes characterized, known as RARa, p, and y (RXR a,P and y)- The various subtypes differ from each other mainly in their amino acid sequence and are encoded in each case by their own gene. Furthermore, one finds isoforms of some of the receptors created by alternative splicing of the primary transcript. Altogether, the repertoire of the various receptor variants is enormously increased through the existence of the subtypes and by alternatively spliced receptors. Because the individual variants differ in their ability to form hetero- and homodimers as well as in their abUity to activate and bind ligands, this results in a great variety of functionally different receptors. 

For techniques not using mutation, the minimum affinity needed in the initial library is that which would be an adequate result from the search. There are no estimates for the repertoire sizes that cover target sequence space with higher minimal affinities however, arguments based on catalytic task space suggest that 10s molecules are sufficient for saturation [4], If enzymes are considered to bind to transitional states between reactants and products, then 10s ligands may be adequate for techniques without mutation. However, there is no estimate for the minimal affinity towards a transitional state needed to catalyze a reaction, so it is unclear what exactly is achieved by a library of this size. 

Linn H, Ermekova KS, Rentschler S, Sparks AB, Kay BK, Sudol M, Using molecular repertoires to identify high-affinity peptide ligands of the WW domain of human and mouse YAP, Biol. Chem., 378(6) 531-537, 1997. 

When acting as a ligand toward two or more metal atoms, alkynes have a large repertoire of roles. With respect to a dimetal unit, there are two major types of structures, both describable as rf, they are shown in Fig. 16-28(c) and (d). In the planar structure of Fig. 16-28(c), the alkyne, is a two-electron donor. In structure... 

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