Crystal Structure of Silkworm Bombyx mori JHBP in Complex With 2-Methyl-2,4-Pentanediol: Plasticity of JH-Binding Pocket and Ligand-Induced Conformational Change of the Second Cavity in JHBP

Zui Fujimoto,Akira Tase,Mitsuru Momma,Wataru Tsuchiya,Rintaro Suzuki,Takahiro Shiotsuki,Toshimasa Yamazaki,Mark J Van Raaij

doi:10.1371/journal.pone.0056261

Abstract

Juvenile hormones (JHs) control a diversity of crucial life events in insects. In Lepidoptera which major agricultural pests belong to, JH signaling is critically controlled by a species-specific high-affinity, low molecular weight JH-binding protein (JHBP) in hemolymph, which transports JH from the site of its synthesis to target tissues. Hence, JHBP is expected to be an excellent target for the development of novel specific insect growth regulators (IGRs) and insecticides. A better understanding of the structural biology of JHBP should pave the way for the structure-based drug design of such compounds. Here, we report the crystal structure of the silkworm Bombyx mori JHBP in complex with two molecules of 2-methyl-2,4-pentanediol (MPD), one molecule (MPD1) bound in the JH-binding pocket while the other (MPD2) in a second cavity. Detailed comparison with the apo-JHBP and JHBP-JH II complex structures previously reported by us led to a number of intriguing findings. First, the JH-binding pocket changes its size in a ligand-dependent manner due to flexibility of the gate α1 helix. Second, MPD1 mimics interactions of the epoxide moiety of JH previously observed in the JHBP-JH complex, and MPD can compete with JH in binding to the JH-binding pocket. We also confirmed that methoprene, which has an MPD-like structure, inhibits the complex formation between JHBP and JH while the unepoxydated JH III (methyl farnesoate) does not. These findings may open the door to the development of novel IGRs targeted against JHBP. Third, binding of MPD to the second cavity of JHBP induces significant conformational changes accompanied with a cavity expansion. This finding, together with MPD2-JHBP interaction mechanism identified in the JHBP-MPD complex, should provide important guidance in the search for the natural ligand of the second cavity.

Highlights

Juvenile hormones (JHs) are acyclic sesquiterpenoids which contain an a,b-unsaturated methyl ester and a terpenoid backbone with an epoxide distal to the ester
Overall Structure of the JH-binding protein (JHBP)-MPD Complex The crystal structure of B. mori JHBP in complex with MPD was solved at a resolution of 2.6 Aby a single-wavelength anomalous dispersion (SAD) method using selenomethionine (SeMet)-substituted crystals (Figure 2 and Table 1)
In this paper, we present the crystal structure of the recombinant B. mori JHBP in complex with two molecules of MPD (MPD1 and MPD2), where MPD1 is bound in the JHbinding pocket and MPD2 in a second hydrophobic cavity

Summary

Introduction

Juvenile hormones (JHs) are acyclic sesquiterpenoids which contain an a,b-unsaturated methyl ester and a terpenoid backbone with an epoxide distal to the ester. Both the ester and epoxide groups are required for hormone regulatory functions. JH regulates diverse processes including the growth, development, metamorphosis and reproduction of insects [1,2]. The JH levels control the full cycle of insect development from the immature larval stage to the adult form. Insect growth regulators (IGRs) with JH-agonistic or -antagonistic activity have become attractive candidates for insect pest control since the identification of the structure of JH in 1967 [3]. Several JH analogues (JHAs) such as methoprene [4], fenoxycarb [5] and pyriproxyfen [6] have been proven to be effective IGRs and useful as insecticides against household and agricultural pests that cause damage worth billions of pounds to global agriculture each year

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