Structural basis of pheromone binding to mouse major urinary protein (MUP‐I)

Abstract

The mouse major urinary proteins are pheromone-binding proteins that function as carriers of volatile effectors of mouse physiology and behavior. Crystal structures of recombinant mouse major urinary protein-I (MUP-I) complexed with the synthetic pheromones, 2-sec-butyl-4,5-dihydrothiazole and 6-hydroxy-6-methyl-3-heptanone, have been determined at high resolution. The purification of MUP-I from mouse liver and a high-resolution structure of the natural isolate are also reported. These results show the binding of 6-hydroxy-6-methyl-3-heptanone to MUP-I, unambiguously define ligand orientations for two pheromones within the MUP-I binding site, and suggest how different chemical classes of pheromones can be accommodated within the MUP-I ␤-barrel.

High resolution X‐ray structures of mouse major urinary protein nasal isoform in complex with pheromones

“…As previously observed, Y97 occurs near a hairpin turn, falling into a disallowed region of the Ramachandran plot. 24 z We note that all MUP structures, including those presented here, have been determined at pH 4.8-7.2. 21,23,24,[26][27][28][29][30][31][32] The pK a of the conjugate acid of thiazole and pyrazine derivatives is around pH 2, 38,39 thus, the sp2 hybridized nitrogen is less likely to be protonated at the pH of the experiments than is a Glu residue.…”

“…This is consistent with the findings of other groups, where significant difference electron density peaks are observed in the MUP binding pocket even in the absence of exogenously introduced ligand. 21,24,26 Data collection and refinement statistics are presented in Table I.…”

“…In the first X-ray structure of MUP-I, the endogenous ligand was modeled as SBT in a similar inverted orientation. 21 It has since been the consensus, based on higher resolution MUP-I and MUP-II crystal structures 23,24 as well as NMR data 37 that SBT binds to MUP-I and MUP-II in the orientation shown in Figure 5(C), with the branched sec-butyl group oriented toward the base of the cavity. In contrast, alignment of protein backbone atoms reveals several differences in SBT binding between MUP-IV and MUP-I (or MUP-II).…”

“…In contrast, alignment of protein backbone atoms reveals several differences in SBT binding between MUP-IV and MUP-I (or MUP-II). In MUP-IV, the branched sec-butyl group is oriented toward the top of the cavity and the two ordered water molecules that form a hydrogen bond network in MUP-I 24 and MUP-II 23 are absent. Instead, the carboxyl moiety of E118 (G118 in MUP-I and MUP-II) occupies this space, within hydrogen bonding distance to the N3 atom of SBT [ Fig.…”

“…20 The first X-ray crystal structure of MUP 21 confirmed that the mouse MUP belong to the lipocalin superfamily. 22 X-ray and NMR structures of MUP-I and MUP-II have been determined in the presence of SBT 23,24 as well as other ligands. [24][25][26][27][28][29][30][31][32] However, until now, there have been no published structures of a group 4 isoform.…”