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Pheromone binding by polymorphic mouse major urinary proteins
Scott D Sharrow1, Jeffrey L Vaughn, Lukás Zídek
1Institute for Pheromone Research and Department of Chemistry, Indiana University, Bloomington, Indiana 47405-0001, USA.
Abstract:
Mouse major urinary proteins (MUPs) have been proposed to play a role in regulating the release and capture of pheromones. Here, we report affinity measurements of five recombinant urinary MUP isoforms (MUPs-I, II, VII, VIII, and IX) and one recombinant nasal isoform (MUP-IV) for each of three pheromonal ligands, (+/-)-2-sec-butyl-4,5-dihydrothiazole (SBT), 6-hydroxy-6-methyl-3-heptanone (HMH), and (+/-)dehydro-exo-brevicomin (DHB). Dissociation constants for all MUP-pheromone pairs were determined by isothermal titration calorimetry, and data for SBT were corroborated by measurements of intrinsic protein fluorescence. We also report the isolation of MUP-IV protein from mouse nasal extracts, in which MUP-IV mRNA has been observed previously. The affinity of each MUP isoform for SBT (K(d) approximately 0.04 to 0.9 micro M) is higher than that for DHB (K(d) approximately 26 to 58 micro M), which in turn is higher than that for HMH (K(d) approximately 50 to 200 micro M). Isoforms I, II, VIII, and IX show very similar affinities for each of the ligands. MUP-VII has approximately twofold higher affinity for SBT but approximately twofold lower affinity for the other pheromones, whereas MUP-IV has approximately 23-fold higher affinity for SBT and approximately fourfold lower affinity for the other pheromones. The variations in ligand affinities of the MUP isoforms are consistent with structural differences in the binding cavities of the isoforms. The data indicate that the concentrations of available pheromones in urine may be influenced by changes in the expression levels of urinary MUPs or the excretion levels of other MUP ligands. The variation in pheromone affinities of the urinary MUP isoforms provides only limited support for the proposal that MUP heterogeneity plays a role in regulating profiles of available pheromones. However, the binding data support the proposed role of nasal MUPs in sequestering pheromones and possibly transporting them to their receptors.
Insights
Mouse major urinary proteins (MUPs) bind pheromones with varying affinities. Nasal MUP-IV shows high affinity for pheromones, suggesting a role in pheromone transport and receptor interaction.
Area of Science:
- Biochemistry
- Animal Behavior
- Molecular Biology
Background:
- Mouse major urinary proteins (MUPs) are implicated in pheromone regulation.
- Understanding MUP-pheromone interactions is key to deciphering olfactory communication.
Purpose of the Study:
- To quantify the binding affinities of various MUP isoforms to key pheromonal ligands.
- To investigate the role of MUP isoforms in pheromone sequestration and transport.
Main Methods:
- Recombinant expression of five urinary MUP isoforms (MUPs-I, II, VII, VIII, IX) and one nasal isoform (MUP-IV).
- Isothermal titration calorimetry and intrinsic protein fluorescence to determine dissociation constants (K(d)) for MUP-pheromone pairs.
- Isolation of MUP-IV protein from mouse nasal extracts.
Main Results:
- MUP isoforms exhibit differential binding affinities for pheromones: (+/-)-2-sec-butyl-4,5-dihydrothiazole (SBT), 6-hydroxy-6-methyl-3-heptanone (HMH), and (+/-)dehydro-exo-brevicomin (DHB).
- SBT binding affinities (K(d) ~0.04–0.9 µM) were significantly higher than DHB (~26–58 µM) and HMH (~50–200 µM).
- Nasal MUP-IV displayed a notably higher affinity for SBT compared to urinary MUPs.
Conclusions:
- Structural variations in MUP binding cavities correlate with observed differences in pheromone ligand affinities.
- While urinary MUP heterogeneity offers limited support for regulating pheromone profiles, nasal MUPs likely play a role in pheromone sequestration and delivery to receptors.